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Frustration-induced degenerate spin state with up-up-down-down ordering in corner-connected Heisenberg square-plaquettes
Authors:
Pritam Manna,
A. K. Bera
Abstract:
We investigate frustrated magnetism of a corner-connected square plaquette Heisenberg model with exchange interactions along the edges $(J_1)$, along inter-plaquette links $(J_2)$, and along square diagonals $(J_3)$. Using Luttinger--Tisza (LT) minimization of the Fourier interaction matrix $\mathcal J(\mathbf q)$ together with large-scale Monte Carlo (MC) simulations, we obtain a classical low-te…
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We investigate frustrated magnetism of a corner-connected square plaquette Heisenberg model with exchange interactions along the edges $(J_1)$, along inter-plaquette links $(J_2)$, and along square diagonals $(J_3)$. Using Luttinger--Tisza (LT) minimization of the Fourier interaction matrix $\mathcal J(\mathbf q)$ together with large-scale Monte Carlo (MC) simulations, we obtain a classical low-temperature magnetic phase diagram in the normalized plane $(J_1/|J_2|, J_3/|J_2|)$. The two methods play complementary roles: the LT analysis provides the zero-temperature candidate ordering wave vectors, while the MC simulations elucidate the resulting ordering tendencies under the hard-spin constraint at low but finite temperatures. Three regimes emerge at low temperatures, an antiferromagnetic phase (AF), a ferromagnetic phase (FM) and a degenerate spin state with \textit{up-up-down-down (uudd)} ordering (DS). For the frustrated degenerate spinstate, LT exhibits line-like minima along $q_x=\pm q_y$ in the $hk$-plane, revealing a highly degenerate spin configuration which violates the hard-spin constraint. The MC results uncover a state with quasi-two-dimensional ordering. The DS regime is intrinsically multi-$\mathbf{q}$: the ordered texture assembles itself from symmetry-related modes on the lines, producing a ``\textit{uudd}'' spin arrangement comprising of distinctive strong antiferromagnetic correlations on diagonals, ferromagnetic correlations on corner links, and highly suppressed correlations on the edges. The field-temperature phase diagram for a representative parameter point in the DS regime, determined by MC simulations, yields field induced distinct regions of negatively and positively correlated layers. These two regions are separated by a curve corresponding to negligible inter-layer correlations.
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Submitted 25 August, 2026;
originally announced August 2026.
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Unconventional Superconductivity in the Chiral Topological Semimetal Ag2Pd3S
Authors:
Roshan Kumar Kushwaha,
Dibyendu Samanta,
Sudarshan Sharma,
Mathew Pula,
Shashank Srivastava,
Poulami Manna,
Arushi,
Sajilesh K. P.,
Suhani Sharma,
Priya Mishra,
Prabin Kumar Naik,
James Beare,
Yipeng Cai,
Kenji M. Kojima,
Amit Kanigel,
Graeme M. Luke,
Sudeep Kumar Ghosh,
Ravi Prakash Singh
Abstract:
Chiral crystals provide a unique setting where broken inversion symmetry, strong spin-orbit coupling, and electronic topology intertwine, yet superconductivity in intrinsically chiral materials remains rare. Here, we report unconventional superconductivity in the chiral topological semimetal Ag$_2$Pd$_3$S, an enantiomorphic analog of natural mineral coldwellite, crystallizing in the right-handed s…
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Chiral crystals provide a unique setting where broken inversion symmetry, strong spin-orbit coupling, and electronic topology intertwine, yet superconductivity in intrinsically chiral materials remains rare. Here, we report unconventional superconductivity in the chiral topological semimetal Ag$_2$Pd$_3$S, an enantiomorphic analog of natural mineral coldwellite, crystallizing in the right-handed space group $P4_132$. Bulk superconductivity with a transition temperature $T_C = 1.1(2)$ K is confirmed by electrical resistivity, magnetization, and specific-heat measurements. Muon spin rotation and relaxation ($μ$SR) experiments reveal a fully gapped superconducting state that spontaneously time-reversal symmetry (TRS) breaking establishing Ag$_2$Pd$_3$S as the first chiral topological semimetal superconductor exhibiting intrinsic TRS breaking. First-principles calculations uncover multiple multifold band crossings near the Fermi level, hosting Kramers-Weyl, double spin-1, and spin-3/2 quasiparticles with large topological charges. These unconventional fermions generate symmetry-protected topological surface states and underscore the nontrivial topology of the normal state. Symmetry analysis based on the Ginzburg-Landau theory suggests a loop-supercurrent-ordered superconducting state, yielding a full gap alongside spontaneous TRS breaking. The coexistence of TRS-breaking superconductivity and chiral multifold fermions identifies Ag$_2$Pd$_3$S as a platform for realizing intrinsic superconducting diode effects and chirality-induced spin selectivity, offering a transformative pathway toward dissipationless topological quantum technologies.
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Submitted 29 June, 2026;
originally announced June 2026.
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Emergence of Quasi-two-dimensional Superconductivity in W-doped Bulk Noncentrosymmetric 3$R$-TaSe$_2$
Authors:
P. Manna,
R. P. Singh
Abstract:
Noncentrosymmetric transition-metal dichalcogenides offer a rich environment for the study of unconventional superconducting phenomena. Here, we present a comprehensive analysis of single-crystalline W-doped 3$R$-TaSe$_2$, revealing weakly coupled anisotropic unconventional superconductivity at $T_c$ = 2.82(2) K, with an in-plane upper critical field exceeding the Pauli limit by 1.7 times. The ang…
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Noncentrosymmetric transition-metal dichalcogenides offer a rich environment for the study of unconventional superconducting phenomena. Here, we present a comprehensive analysis of single-crystalline W-doped 3$R$-TaSe$_2$, revealing weakly coupled anisotropic unconventional superconductivity at $T_c$ = 2.82(2) K, with an in-plane upper critical field exceeding the Pauli limit by 1.7 times. The angular dependence of the upper critical field, along with the observation of a Berezinskii-Kosterlitz-Thouless transition, reveals quasi-two-dimensional superconductivity. Crucially, magnetotransport reveals a distinct two-fold rotational symmetry within the superconducting state under in-plane fields, breaking the underlying three-fold lattice symmetry. These findings establish W-doped $3R\text{-TaSe}_2$ as a bulk model system for exploring intrinsic low-dimensional superconductivity and broken rotational symmetry, thus opening new directions for future quantum technologies.
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Submitted 24 June, 2026;
originally announced June 2026.
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Enhanced Spin-to-Charge Conversion in Bi2Se3/NiFe via Interface Engineering with a Ti Spacer Layer
Authors:
Sourav Rajat Subhra Maitra,
Poulami Manna,
Ravi Prakash Singh,
Chandrasekhar Murapaka,
Arabinda Haldar
Abstract:
Topological insulators have attracted significant attention in spintronics due to their topological surface states and spin-momentum-locking-driven spin-to-charge conversion. Among these, Bi2Se3 has been extensively investigated because of its large bulk bandgap and single Dirac cone band structure. However, spin-to-charge conversion strongly depends on the quality of the topological insulator/fer…
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Topological insulators have attracted significant attention in spintronics due to their topological surface states and spin-momentum-locking-driven spin-to-charge conversion. Among these, Bi2Se3 has been extensively investigated because of its large bulk bandgap and single Dirac cone band structure. However, spin-to-charge conversion strongly depends on the quality of the topological insulator/ferromagnet interface. Here, we investigate spin-to-charge conversion in a sputter-deposited heterostructure comprising a topological insulator (Bi2Se3) and a ferromagnetic NiFe thin film separated by a titanium spacer layer. The Bi2Se3 layer is deposited on a silicon substrate for industrial compatibility. Pure spin current is injected into the Bi2Se3 layer through the titanium spacer via spin pumping induced by spin precession during microwave-driven ferromagnetic resonance of the ferromagnetic film. Spin pumping studies are performed by varying the Bi2Se3 thickness. The Gilbert damping parameter exhibits a significant 55% increase at a Bi2Se3 thickness of 4 nm, indicating a pure surface-state contribution. The spin Hall angle, which quantifies the spin-to-charge conversion efficiency, increases by an order of magnitude upon insertion of the titanium spacer layer. This enhancement is attributed to the suppression of interdiffusion between the Bi2Se3 and NiFe layers by titanium, thereby preserving the topological surface states. These findings highlight the important role of titanium spacer layers in spintronic devices based on topological materials.
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Submitted 31 May, 2026;
originally announced June 2026.
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Discovery of Quasi One Dimensional Superconductivity in PtPb3Bi
Authors:
Shashank Srivastava,
Yash Vardhan,
Anshu Kataria,
Pradyumna Bawankule,
Poulami Manna,
Prabin Kumar Naik,
Rahul Verma,
Rhea Stewart,
James S. Lord,
Adrian D. Hillier,
Mathias S. Scheurer,
D. T. Adroja,
Bahadur Singh,
Ravi Prakash Singh
Abstract:
Quasi one dimensional materials provide a compelling platform where reduced dimensionality stabilizes intertwined topological and superconducting phases. Here we report superconductivity in a new Bi based quasi 1D compound, PtPb3Bi, which hosts a nontrivial electronic structure. It exhibits type II superconductivity below 3.01(1) K. Heat capacity and transverse field muon spin rotation relaxation…
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Quasi one dimensional materials provide a compelling platform where reduced dimensionality stabilizes intertwined topological and superconducting phases. Here we report superconductivity in a new Bi based quasi 1D compound, PtPb3Bi, which hosts a nontrivial electronic structure. It exhibits type II superconductivity below 3.01(1) K. Heat capacity and transverse field muon spin rotation relaxation (muSR) measurements demonstrate a fully gapped isotropic s wave state with moderate electron phonon coupling, while zero field muSR confirms the preservation of time reversal symmetry (TRS). Transport measurements reveal low carrier mobility with diffusive normal state transport. Electronic structure calculations show strong dispersion along the quasi 1D direction and relatively flatter bands in the transverse plane, giving rise to pronounced Fermi surface nesting in the kx-ky plane. Consistent with this, the compound undergoes a charge density wave transition at 280(1) K. The flow of Wannier charge centers, together with surface state dispersion, establishes nontrivial band topology. These results identify PtPb3Bi as a new quasi 1D superconductor with nontrivial electronic structure and a promising candidate for topological superconductivity.
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Submitted 6 April, 2026;
originally announced April 2026.
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Hourglass Dirac chains enable intrinsic topological superconductivity in nonsymmorphic silicides
Authors:
Shashank Srivastava,
Dibyendu Samanta,
Pavan Kumar Meena,
Poulami Manna,
Priya Mishra,
Suhani Sharma,
Prabin Kumar Naik,
Rhea Stewart,
Adrian D. Hillier,
Sudeep Kumar Ghosh,
Ravi Prakash Singh
Abstract:
Nonsymmorphic crystalline symmetries provide a robust route to symmetry-protected electronic topology, yet their role in stabilizing intrinsic topological superconductivity remains largely unexplored. Here, we report \ch{TaPtSi} as a new member of the superconducting nonsymmorphic silicide family, characterized via AC transport, magnetization, heat capacity, and muon spin rotation/relaxation ($μ$S…
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Nonsymmorphic crystalline symmetries provide a robust route to symmetry-protected electronic topology, yet their role in stabilizing intrinsic topological superconductivity remains largely unexplored. Here, we report \ch{TaPtSi} as a new member of the superconducting nonsymmorphic silicide family, characterized via AC transport, magnetization, heat capacity, and muon spin rotation/relaxation ($μ$SR) measurements. Zero field $μ$SR reveals spontaneous internal magnetic fields below $T_{\rm c}$, establishing time reversal symmetry breaking in \ch{TaPtSi}. First principles calculations on \ch{TaPtSi} and its isostructural nonsymmorphic superconducting analogues reveal the presence of symmetry-protected hourglass dispersions. The "necks" of these dispersions form Dirac nodal rings and chains that reside near or intersect the Fermi level. Guided by Ginzburg Landau symmetry analysis, we identify an internally antisymmetric non unitary triplet pairing state as the unique ground state consistent with the experimental phenomenology. Based on Bogoliubov de Gennes calculations, we further demonstrate that this state supports Majorana surface modes, establishing its intrinsically topological nature. These results reveal a systematic route by which nonsymmorphic symmetry drives the interplay between hourglass Dirac chain topology and unconventional triplet pairing, positioning equiatomic silicides as a unified materials platform for intrinsic topological superconductivity.
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Submitted 26 February, 2026;
originally announced February 2026.
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Topological and Planar Hall Effect in Monoclinic van der Waals Ferromagnet NbFeTe$_2$
Authors:
Suchanda Mondal,
Shubhankar Roy,
Poulami Manna,
Ravi Prakash Singh
Abstract:
Two-dimensional (2D) van der Waals (vdW) ferromagnets have emerged as a critical class of quantum materials for next-generation, low-dimensional spintronic devices. In this study, we report a comprehensive study of the transport properties of the layered soft ferromagnet $\text{NbFeTe}_2$. We report the first observation of the topological Hall effect (THE) and the planar Hall effect (PHE) in meta…
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Two-dimensional (2D) van der Waals (vdW) ferromagnets have emerged as a critical class of quantum materials for next-generation, low-dimensional spintronic devices. In this study, we report a comprehensive study of the transport properties of the layered soft ferromagnet $\text{NbFeTe}_2$. We report the first observation of the topological Hall effect (THE) and the planar Hall effect (PHE) in metallic $\text{NbFeTe}_2$. THE signatures persist up to 45 K, while PHE remains evident well above Curie temperature ($T_C$). The observed negative longitudinal magnetoresistance, along with the PHE, provides strong evidence for a nontrivial electronic band structure. The coexistence of perpendicular magnetic anisotropy and a substantial THE: two key properties that are highly desirable for future spintronics applications, makes monoclinic vdW ferromagnetic $\text{NbFeTe}_2$ a promising platform to advance spintronics applications.
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Submitted 7 February, 2026;
originally announced February 2026.
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Observation of Time-Reversal Symmetry Breaking in the Type-I Superconductor YbSb$_2$
Authors:
Anshu Kataria,
Shashank Srivastava,
Dibyendu Samanta,
Pushpendra Yadav,
Poulami Manna,
Suhani Sharma,
Priya Mishra,
Joel Barker,
Adrian D. Hillier,
Amit Agarwal,
Sudeep Kumar Ghosh,
Ravi Prakash Singh
Abstract:
The spontaneous breaking of time-reversal symmetry is a hallmark of unconventional superconductivity, typically observed in type-II superconductors. Here, we report evidence of time-reversal symmetry breaking in the type-I superconductor YbSb$_2$. Zero-field $μ$SR measurements reveal spontaneous internal magnetic fields emerging just below the superconducting transition, while transverse-field…
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The spontaneous breaking of time-reversal symmetry is a hallmark of unconventional superconductivity, typically observed in type-II superconductors. Here, we report evidence of time-reversal symmetry breaking in the type-I superconductor YbSb$_2$. Zero-field $μ$SR measurements reveal spontaneous internal magnetic fields emerging just below the superconducting transition, while transverse-field $μ$SR confirms a fully gapped type-I superconducting state. Our first-principles calculations identify YbSb$_2$ as a ${\mathbb Z}_2$ topological metal hosting a Dirac nodal line near the Fermi level. Symmetry analysis within the Ginzburg Landau framework indicates an internally antisymmetric nonunitary triplet (INT) state as the most probable superconducting ground state. Calculations based on an effective low-energy model further demonstrate that this INT state hosts gapless Majorana surface modes, establishing YbSb$_2$ as a topological superconductor. Our results highlight YbSb$_2$ as a unique material platform where type-I superconductivity coexists with triplet-pairing and nontrivial topology.
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Submitted 12 January, 2026;
originally announced January 2026.
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Evidence of anisotropic bulk superconductivity in disorder-induced ZrTe$_{3-x}$
Authors:
P. Manna,
C. Patra,
T. Agarwal,
S. Srivastava,
S. Sharma,
P. Mishra,
R. P. Singh
Abstract:
Transition-metal trichalcogenides distinguish themselves from other two-dimensional materials in nanoscience and materials science due to their remarkable range of intrinsic properties, including various electronic, optical, and magnetic behaviors. Here, we report a comprehensive study of superconductivity in disordered ZrTe$_{3-x}$ ($x$ = 0.2) with suppressed charge density wave. We observe a typ…
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Transition-metal trichalcogenides distinguish themselves from other two-dimensional materials in nanoscience and materials science due to their remarkable range of intrinsic properties, including various electronic, optical, and magnetic behaviors. Here, we report a comprehensive study of superconductivity in disordered ZrTe$_{3-x}$ ($x$ = 0.2) with suppressed charge density wave. We observe a type-II bulk anisotropic superconductivity with a superconducting transition at $T_c$ = 3.59(4) \si{K}. Angle-dependent upper critical field measurements and Berezinskii-Kosterlitz-Thouless transition confirm the inherent quasi-two-dimensional nature of superconductivity in this disordered system.
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Submitted 5 January, 2026;
originally announced January 2026.
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Probing the intermediate state of type-I superconductor SnAs using Muon Spin Spectroscopy
Authors:
Shashank Srivastava,
Omkar Kulkarni,
Arushi,
Deepak Singh,
Poulami Manna,
Priya Mishra,
Suhani Sharma,
Pabitra Kumar Biswas,
Rhea Stewart,
Adrian D. Hillier,
Ravi Prakash Singh
Abstract:
Superconductivity with non-trivial band topology provides a novel platform for exploring topological superconductivity and its quantum applications. A detailed microscopic understanding of the superconducting ground state in such materials is crucial. Here, we report the results of a muon spin rotation/relaxation study ($μ$SR) of the topologically non-trivial superconductor SnAs, which exhibits su…
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Superconductivity with non-trivial band topology provides a novel platform for exploring topological superconductivity and its quantum applications. A detailed microscopic understanding of the superconducting ground state in such materials is crucial. Here, we report the results of a muon spin rotation/relaxation study ($μ$SR) of the topologically non-trivial superconductor SnAs, which exhibits superconductivity below 3.74(1) \si{K}. Zero-field (ZF) $μ$SR data reveal that this system is a time-reversal invariant superconductor, and systematic transverse-field (TF) $μ$SR measurements unveil the type-I nature of the SnAs superconductor. We have established the superconducting phase diagram to understand the intermediate state of type-I superconductors. Moreover, ab \textit{initio} band structure and phonon calculations are performed, which correlate with the experimental characterization.
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Submitted 19 December, 2025;
originally announced December 2025.
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Pattern formation in ring condensates subjected to bichromatic driving
Authors:
Premabrata Manna,
S. I. Mistakidis,
P. G. Kevrekidis,
Pankaj Kumar Mishra
Abstract:
We investigate the dynamical formation of nonlinear patterns in one-dimensional ring condensates under bichromatic periodic modulation of the interaction strength. The stability phase diagram of the condensate's homogeneous density state is analytically derived through a suitable biharmonic variant of the Mathieu equation and computing the associated Floquet spectrum. It reveals the complex interp…
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We investigate the dynamical formation of nonlinear patterns in one-dimensional ring condensates under bichromatic periodic modulation of the interaction strength. The stability phase diagram of the condensate's homogeneous density state is analytically derived through a suitable biharmonic variant of the Mathieu equation and computing the associated Floquet spectrum. It reveals the complex interplay between the driving parameters, i.e., amplitude, frequencies, and the so-called frequencies' mixing angle, which dictate the instability onset and the selective enhancement of higher-order resonance tongues, thus offering precise control over the excited modes. These results are in agreement with time-dependent mean-field simulations evidencing the emergence of density wave modulations of specific momenta, while enabling a deeper understanding of the nonlinear stage of the relevant instability. Further insights on the ensuing unstable nonlinear dynamics are provided through a reduced {five-mode} model which captures the instability onset, the oscillatory behavior of the mode populations and the phase-space dynamics, in agreement with the mean-field predictions. Our study highlights the versatility of bichromatic driving to generate and control complex nonlinear patterns that are within reach in present day ultracold atom experiments.
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Submitted 10 November, 2025;
originally announced November 2025.
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Quasi-two-dimensional superconductivity in 1$T$-Ti$_{1-x}$Ta$_x$Se$_2$
Authors:
P. Manna,
S. Sharma,
T. Agarwal,
S. Srivastava,
P. Mishra,
R. P. Singh
Abstract:
The emergence of two-dimensional (2D) superconductivity in bulk transition metal dichalcogenides (TMDs) is a fascinating area of research, as their weak interlayer coupling leads to novel superconducting behavior and offers a rich platform to host nontrivial gap structures and interactions with other electronic orders. In this work, we present a comprehensive study of the superconducting propertie…
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The emergence of two-dimensional (2D) superconductivity in bulk transition metal dichalcogenides (TMDs) is a fascinating area of research, as their weak interlayer coupling leads to novel superconducting behavior and offers a rich platform to host nontrivial gap structures and interactions with other electronic orders. In this work, we present a comprehensive study of the superconducting properties of bulk single-crystalline $1T$-Ti$_{1-x}$Ta$_x$Se$_2$ for x = 0.2. Our results confirm the weakly coupled anisotropic superconductivity. Angle-dependent upper critical field measurements and observation of a Berezinskii-Kosterlitz-Thouless transition confirm the quasi-2D nature of the superconducting state. These results position $1T$-Ti$_{1-x}$Ta$_x$Se$_2$ as a promising platform for exploring low-dimensional superconducting physics and highlight bulk TMD crystals as a promising platform for realizing intrinsic 2D superconductivity, opening avenues for future quantum applications.
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Submitted 1 November, 2025;
originally announced November 2025.
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Nonsymmorphic symmetry protected hourglass Dirac chain topology and conventional superconductivity in ZrIrGe
Authors:
Pavan Kumar Meena,
Dibyendu Samanta,
Shashank Srivastava,
Poulami Manna,
Sudeep Kumar Ghosh,
Ravi Prakash Singh
Abstract:
Ternary transition-metal germanide superconductors with nonsymmorphic symmetries offer promising platforms for symmetry-protected topological phases. In this work, we investigate ZrIrGe, which crystallizes in the nonsymmorphic TiNiSi-type structure. Electrical, magnetic, and specific heat measurements confirm bulk type-II superconductivity with a full gap and a transition temperature of 2.84(7) K,…
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Ternary transition-metal germanide superconductors with nonsymmorphic symmetries offer promising platforms for symmetry-protected topological phases. In this work, we investigate ZrIrGe, which crystallizes in the nonsymmorphic TiNiSi-type structure. Electrical, magnetic, and specific heat measurements confirm bulk type-II superconductivity with a full gap and a transition temperature of 2.84(7) K, consistent with weak-coupling BCS behavior. First-principles calculations reveal hourglass-shaped bulk band dispersions and a Dirac chain composed of symmetry-protected fourfold-degenerate Dirac points, leading to drumhead-like surface states near the Fermi level. Additionally, ZrIrGe exhibits a nontrivial $\mathbb{Z}_2$ topological character, resulting in helical surface states that cross the Fermi level, making it a strong candidate for proximity-induced topological superconductivity. The coexistence of conventional superconductivity and topological band features establishes ZrIrGe as a rare stoichiometric system for exploring intrinsic topological superconductivity.
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Submitted 3 October, 2025;
originally announced October 2025.
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Ising superconductivity in bulk layered non-centrosymmetric 4H-NbSe2
Authors:
Chandan Patra,
Tarushi Agarwal,
Rahul Verma,
Poulami Manna,
Shashank Srivastava,
Ravi Shankar Singh,
Mathias S. Scheurer,
Bahadur Singh,
Ravi Prakash Singh
Abstract:
Transition metal dichalcogenides exhibit multiple polymorphs that enable the exploration of diverse quantum states, including valley-selective spin polarization, the valley Hall effect, Ising superconductivity, and nontrivial topology. Monolayer 2$H$-NbSe$_2$ is a promising candidate for realizing Ising superconductivity due to its spin-split, out-of-plane spin-polarized states arising from invers…
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Transition metal dichalcogenides exhibit multiple polymorphs that enable the exploration of diverse quantum states, including valley-selective spin polarization, the valley Hall effect, Ising superconductivity, and nontrivial topology. Monolayer 2$H$-NbSe$_2$ is a promising candidate for realizing Ising superconductivity due to its spin-split, out-of-plane spin-polarized states arising from inversion symmetry breaking and strong spin-orbit coupling. In contrast, bulk 2$H$-NbSe$_2$ retains inversion symmetry and lacks spin splitting, limiting its suitability for hosting Ising superconductivity. Here, we report the growth of high-quality single crystals of the acentric bulk superconducting polymorph, 4$H$-NbSe$_2$, which intrinsically breaks the inversion symmetry and supports valley-selective spin-polarized states. Magnetization and resistivity measurements reveal anisotropic superconductivity, with the in-plane upper critical field exceeding the Pauli limit, while out-of-plane fields suppress superconductivity more rapidly, before reaching the Pauli limit, which strongly suggests the presence of Ising pairing. First-principles calculations and symmetry analysis confirm significant valley-selective spin splitting with out-of-plane spin polarization, further supporting the emergence of Ising superconductivity in 4$H$-NbSe$_2$. These results establish 4$H$-NbSe$_2$ as a robust bulk platform to investigate Ising superconductivity and valley-selective phenomena in transition-metal dichalcogenides.
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Submitted 11 June, 2025;
originally announced June 2025.
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Anomalous Magneto-transport and Anisotropic Multigap Superconductivity in Architecturally Misfit Layered System (PbS)$_{1.13}$TaS$_2$
Authors:
Tarushi Agarwal,
Chandan Patra,
Poulami Manna,
Shashank Srivastava,
Priya Mishra,
Suhani Sharma,
Ravi Prakash Singh
Abstract:
Misfit-layered compounds, naturally occurring bulk heterostructures, present a compelling alternative to artificially engineered ones, offering a unique platform for exploring correlated phases and quantum phenomena. This study investigates the magnetotransport and superconducting properties of the misfit compound (PbS)$_{1.13}$TaS$_2$, comprising alternating PbS and 1$H$-TaS$_2$ layers. It exhibi…
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Misfit-layered compounds, naturally occurring bulk heterostructures, present a compelling alternative to artificially engineered ones, offering a unique platform for exploring correlated phases and quantum phenomena. This study investigates the magnetotransport and superconducting properties of the misfit compound (PbS)$_{1.13}$TaS$_2$, comprising alternating PbS and 1$H$-TaS$_2$ layers. It exhibits distinctive transport properties, including a prominent planar Hall effect and a four-fold oscillatory Butterfly-shaped anisotropic magnetoresistance (AMR). Moreover, it shows multigap two-dimensional superconductivity with an exceptionally high in-plane upper critical field, exceeding the Pauli limit. The coexistence of unconventional superconductivity and anomalous transport - two distinct quantum phenomena, within the same material, suggests that misfit compounds provide an ideal platform for realizing quantum effects in the two-dimensional limit of bulk crystals. This opens the door to the development of simpler and more efficient quantum devices.
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Submitted 6 January, 2025;
originally announced January 2025.
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High critical field superconductivity in a 3d dominated lightweight equiatomic high entropy alloy
Authors:
S. Jangid,
P. K. Meena,
R. K. Kushwaha,
S. Srivastava,
P. Manna,
S. Sharma,
P. Mishra,
R. P. Singh
Abstract:
The lightweight high entropy alloy represents an innovative class of multicomponent systems that combine low density with the exceptional mechanical properties of high-entropy alloys. We present a detailed synthesis and investigation of a 3d rich equiatomic high entropy alloy superconductor Sc-Ti-V-Nb-Cu, which crystallizes in a body-centered cubic structure. Magnetization, electrical resistivity,…
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The lightweight high entropy alloy represents an innovative class of multicomponent systems that combine low density with the exceptional mechanical properties of high-entropy alloys. We present a detailed synthesis and investigation of a 3d rich equiatomic high entropy alloy superconductor Sc-Ti-V-Nb-Cu, which crystallizes in a body-centered cubic structure. Magnetization, electrical resistivity, and heat capacity measurements confirm weakly coupled bulk type II superconductivity with a 7.21(3) K transition temperature and an upper critical field of 12.9(1) T. The upper critical field approaches the Pauli paramagnetic limit, suggesting potential unconventional behavior. The low density, moderate transition temperature, and high upper critical field stand out Sc-Ti-V-Nb-Cu as a promising candidate for next-generation superconducting device applications.
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Submitted 3 January, 2025;
originally announced January 2025.
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Stabilization of Ambient Pressure Rocksalt Crystal Structure and High Critical Field Superconductivity in ReC via Mo and W Substitution
Authors:
P. K. Meena,
S. Jangid,
R. K. Kushwaha,
P. Manna,
S. Sharma,
P. Mishra,
R. P. Singh
Abstract:
Transition-metal-based carbides (TMCs), renowned for their exceptional hardness, mechanical strength, and thermal properties, have recently emerged as promising candidates for topological superconductivity. In this study, we synthesized ReC in the NaCl structure at ambient pressure by substituting Mo or W at the Re-site. We investigated the superconducting properties of Re$_{1-x}$T$_{x}$C (where T…
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Transition-metal-based carbides (TMCs), renowned for their exceptional hardness, mechanical strength, and thermal properties, have recently emerged as promising candidates for topological superconductivity. In this study, we synthesized ReC in the NaCl structure at ambient pressure by substituting Mo or W at the Re-site. We investigated the superconducting properties of Re$_{1-x}$T$_{x}$C (where T = Mo, W) for $x = 0.5$ using magnetization, resistivity and specific heat measurements. These compounds display type-II, fully gapped, weakly coupled superconductivity with high critical fields, establishing them as new members of superconducting ultra-hard materials at ambient pressure and paving the way for superconducting device applications under extreme conditions.
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Submitted 5 September, 2024;
originally announced September 2024.
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Superconductivity with high upper critical field in an equiatomic high entropy alloy Sc-V-Ti-Hf-Nb
Authors:
S. Jangid,
P. K. Meena,
R. K. Kushwaha,
S. Srivastava,
P. Manna,
P. Mishra,
S. Sharma,
R. P. Singh
Abstract:
High-entropy alloy (HEA) superconductors have attracted significant attention due to their exceptional low-temperature mechanical and superconducting properties. We report the synthesis and thorough characterization of an equiatomic HEA superconductor with the composition Sc$_{0.20}$V$_{0.20}$Ti$_{0.20}$Hf$_{0.20}$Nb$_{0.20}$, crystallizing in a body-centered cubic crystal structure (Im3$\bar{m}$)…
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High-entropy alloy (HEA) superconductors have attracted significant attention due to their exceptional low-temperature mechanical and superconducting properties. We report the synthesis and thorough characterization of an equiatomic HEA superconductor with the composition Sc$_{0.20}$V$_{0.20}$Ti$_{0.20}$Hf$_{0.20}$Nb$_{0.20}$, crystallizing in a body-centered cubic crystal structure (Im3$\bar{m}$). Our investigation, using magnetization, transport, and heat capacity measurements, reveals the presence of weakly coupled, fully gapped superconductivity with a transition temperature of 4.17(3) K and the upper critical field exceeding the Pauli paramagnetic limit. The metallic nature, combined with a high upper critical field, positions it as a promising candidate for applications in superconducting devices.
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Submitted 26 April, 2024;
originally announced April 2024.
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Superconductivity in new family of Rhenium-based binary alloys: Re$_{7}$X$_{3}$ (X = Nb, Ta, Ti, Zr, Hf)
Authors:
R. K. Kushwaha,
P. K. Meena,
S. Jangid,
P. Manna,
S. Srivastava,
T. Kumari,
S. Sharma,
P. Mishra,
R. P. Singh
Abstract:
Rhenium-based superconductors have recently attracted significant interest due to their unconventional superconducting properties. In this work, we report the synthesis and properties of new superconducting Re$_{7}$X$_{3}$ (X = Nb, Ta, Ti, Zr, Hf) binary alloys which maintain a fixed composition of rhenium while crystallizing in centrosymmetric to non-centrosymmetric crystal structures, depending…
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Rhenium-based superconductors have recently attracted significant interest due to their unconventional superconducting properties. In this work, we report the synthesis and properties of new superconducting Re$_{7}$X$_{3}$ (X = Nb, Ta, Ti, Zr, Hf) binary alloys which maintain a fixed composition of rhenium while crystallizing in centrosymmetric to non-centrosymmetric crystal structures, depending on the elements of the X site. Comprehensive structural and superconducting properties were investigated using powder x-ray diffraction, AC transport, magnetization, and specific heat measurements, and on the basis of these measurements, the superconducting phase diagram was constructed. The results suggest a complex interplay of crystal structure and the Re/X ratio, which governs the strength of spin-orbital coupling and controls the unconventional superconducting behavior in Re-based superconductors.
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Submitted 12 February, 2024;
originally announced February 2024.
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Superconductivity in Breathing Kagome-Structured C14 Laves Phase XOs2(X = Zr, Hf)
Authors:
P. K. Meena,
M. Mandal,
P. Manna,
S. Srivastava,
S. Sharma,
P. Mishra,
R. P. Singh
Abstract:
Recently, the emergence of superconductivity in kagome metals has generated significant interest due to its interaction with flat bands and topological electronic states, which exhibit a range of unusual quantum characteristics. This study thoroughly investigates largely unexplored breathing Kagome structure C14 laves phase compounds XOs$_{2}$ (X = Zr, Hf) by XRD, electrical transport, magnetizati…
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Recently, the emergence of superconductivity in kagome metals has generated significant interest due to its interaction with flat bands and topological electronic states, which exhibit a range of unusual quantum characteristics. This study thoroughly investigates largely unexplored breathing Kagome structure C14 laves phase compounds XOs$_{2}$ (X = Zr, Hf) by XRD, electrical transport, magnetization, and specific heat measurements. Our analyses confirm the presence of the MgZn$_{2}$-type structure in ZrOs$_{2}$ and HfOs$_{2}$ compounds, exhibiting type-II superconductivity with critical temperature (T$_{C}$) values of 2.90(3) K and 2.69(6) K, respectively. Furthermore, specific heat measurements and an electron-phonon coupling constant suggest the presence of weakly coupled BCS superconductivity in both compounds.
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Submitted 15 January, 2024;
originally announced January 2024.
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Superconducting Properties of Topological Semimetal 1$T$-RhSeTe
Authors:
C. Patra,
T. Agarwal,
Arushi,
P. Manna,
N. Bhatt,
R. S. Singh,
R. P. Singh
Abstract:
Platinum-group transition-metal dichalcogenides have emerged as a subject of considerable interest in condensed matter physics due to their remarkable topological properties and unconventional superconducting behavior. In this study, we report the synthesis and superconducting characteristics of a new Dirac-type topological semimetallic compound 1$T$-RhSeTe. It shows type-II superconductivity with…
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Platinum-group transition-metal dichalcogenides have emerged as a subject of considerable interest in condensed matter physics due to their remarkable topological properties and unconventional superconducting behavior. In this study, we report the synthesis and superconducting characteristics of a new Dirac-type topological semimetallic compound 1$T$-RhSeTe. It shows type-II superconductivity with a superconducting transition temperature of 4.72 K and a high upper critical field. The coexistence of superconductivity and topological properties makes it a prime candidate for hosting topological superconductivity.
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Submitted 2 November, 2023;
originally announced November 2023.
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Effect of spin glass frustration on exchange bias in NiMn/CoFeB bilayers
Authors:
Sagarika Nayak,
Palash Kumar Manna,
Braj Bhusan Singh,
Subhankar Bedanta
Abstract:
Exchange bias in ferromagnetic/antiferromagnetic systems can be explained in terms of various interfacial phenomena. Among these spin glass frustration can affect the magnetic properties in exchange bias systems. Here we have studied a NiMn/CoFeB exchange bias system in which spin glass frustration seems to play a crucial role. In order to account the effect of spin glass frustration on magnetic p…
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Exchange bias in ferromagnetic/antiferromagnetic systems can be explained in terms of various interfacial phenomena. Among these spin glass frustration can affect the magnetic properties in exchange bias systems. Here we have studied a NiMn/CoFeB exchange bias system in which spin glass frustration seems to play a crucial role. In order to account the effect of spin glass frustration on magnetic properties, we have performed the temperature and cooling field dependence of exchange bias. We have observed the decrease of exchange bias field (HEB) with cooling field (HFC) whereas there is not significant effect on coercive field (HC). Exponential decay of HEB and HC is found in these exchange bias systems. Further, training effect measurements have been performed to study the spin relaxation mechanism. We have fitted the training effect data with frozen and rotatable spin relaxation model. We have investigated the ratio of relaxation rate of interfacial rotatable and frozen spins in this study. The training effect data are also fitted with various other models. Further, we observed the shifting of peak temperature towards higher temperature with frequency from the ac susceptibility data.
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Submitted 31 October, 2020;
originally announced November 2020.
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Temperature and field evolution of site-dependent magnetism in $ε$-Fe$_2$O$_3$ nanoparticles
Authors:
Richard Jones,
Rachel Nickel,
Palash K. Manna,
J. Hilman,
Johan van Lierop
Abstract:
8~nm epsilon-Fe2O3 nanoparticles exhibit a spin reorientation transition that begins at 150 K which is a hallmark of this unique iron-oxide polymorph. We find that the change from the high to low temperature magnetic structures has been suppressed by ~50 K. At the spin reorientation temperature, a change of the field-dependent response of the tetrahedral sites in intermediate field strengths (0.25…
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8~nm epsilon-Fe2O3 nanoparticles exhibit a spin reorientation transition that begins at 150 K which is a hallmark of this unique iron-oxide polymorph. We find that the change from the high to low temperature magnetic structures has been suppressed by ~50 K. At the spin reorientation temperature, a change of the field-dependent response of the tetrahedral sites in intermediate field strengths (0.25 - 1.5 T) indicates that a collective tetrahedral distortion occurs to which the octahedral sites adjust, altering the magnetic anisotropy. An abrupt step in the hyperfine parameters' temperature dependencies, especially at 125 K for the hyperfine field associated with the Fe4 tetrahedral sites, suggests strongly a change in the superexchange pathways are responsible for the spin reorientation.
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Submitted 12 September, 2019;
originally announced September 2019.
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Exchange bias in Fe/Ir20Mn80 bilayers: Role of spin-glass like interface and bulk antiferromagnet spins
Authors:
Sagarika Nayak,
Palash Kumar Manna,
Thiruvengadam Vijayabaskaran,
Braj Bhusan Singh,
Subhankar Bedanta
Abstract:
We have performed magnetic measurements like temperature (T), cooling field (HFC) dependence of exchange bias (EB) and training effect to investigate the magnetic nature of the interface of the Fe/Ir20Mn80 systems. Thin film bilayer samples of different thicknesses of Ir20Mn80 have been prepared by dc magnetron sputtering at room temperature. The variation of exchange bias field (HEB) with the inc…
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We have performed magnetic measurements like temperature (T), cooling field (HFC) dependence of exchange bias (EB) and training effect to investigate the magnetic nature of the interface of the Fe/Ir20Mn80 systems. Thin film bilayer samples of different thicknesses of Ir20Mn80 have been prepared by dc magnetron sputtering at room temperature. The variation of exchange bias field (HEB) with the increase in thickness of Ir20Mn80 predicts the antiferromagnet (AFM) bulk spins contribution to EB. Exponential decay of HEB and coercive field (HC) with temperature reveals the presence of spin glass (SG) like interface. Also, the decrease of HEB with increasing HFC confirms the SG like frustration at the interface. Further, the fitting of training effect experimental data envisages the presence of frozen and rotatable spins at the magnetically frustrated interface of these EB systems.
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Submitted 4 June, 2019;
originally announced June 2019.
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Shape-dependent oriented trapping and scaffolding of plasmonic nanoparticles by topological defects for self-assembly of colloidal dimers in liquid crystals
Authors:
Bohdan Senyuk,
Julian S. Evans,
Paul J. Ackerman,
Taewoo Lee,
Pramit Manna,
Leonid Vigderman,
Eugene R. Zubarev,
Jao van de Lagemaat,
Ivan I. Smalyukh
Abstract:
We demonstrate scaffolding of plasmonic nanoparticles by topological defects induced by colloidal microspheres to match their surface boundary conditions with a uniform far-field alignment in a liquid crystal host. Displacing energetically costly liquid crystal regions of reduced order, anisotropic nanoparticles with concave or convex shapes not only stably localize in defects but also self-orient…
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We demonstrate scaffolding of plasmonic nanoparticles by topological defects induced by colloidal microspheres to match their surface boundary conditions with a uniform far-field alignment in a liquid crystal host. Displacing energetically costly liquid crystal regions of reduced order, anisotropic nanoparticles with concave or convex shapes not only stably localize in defects but also self-orient with respect to the microsphere surface. Using laser tweezers, we manipulate the ensuing nanoparticle-microsphere colloidal dimers, probing the strength of elastic binding and demonstrating self-assembly of hierarchical colloidal superstructures such as chains and arrays.
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Submitted 22 December, 2016;
originally announced December 2016.
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Exchange Bias in BiFe_{0.8}Mn_{0.2}O_3 Nanoparticles with an Antiferromagnetic Core and a Diluted Antiferromagnetic Shell
Authors:
P. K. Manna,
S. M. Yusuf,
R. Shukla,
A. K. Tyagi
Abstract:
We have observed conventional signature of exchange bias (EB), in form of shift in field-cooled (FC) hysteresis loop, and training effect, in BiFe0.8Mn0.2O3 nanoparticles. From neutron diffraction, thermoremanent magnetization and isothermoremanent magnetization measurements, the nanoparticles are found to be core-shell in nature, consisting of an antiferromagnetic (AFM) core, and a 2-dimensional…
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We have observed conventional signature of exchange bias (EB), in form of shift in field-cooled (FC) hysteresis loop, and training effect, in BiFe0.8Mn0.2O3 nanoparticles. From neutron diffraction, thermoremanent magnetization and isothermoremanent magnetization measurements, the nanoparticles are found to be core-shell in nature, consisting of an antiferromagnetic (AFM) core, and a 2-dimensional diluted AFM (DAFF) shell with a net magnetization under a field. The analysis of the training effect data using the Binek's model shows that the observed loop shift arises entirely due to an interface exchange coupling between core and shell, and the intrinsic contribution of the DAFF shell to the total loop shift is zero. A significantly high value of EB field has been observed at room temperature. The present study is useful to understand the origin of EB in other DAFF-based systems as well.
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Submitted 10 May, 2011;
originally announced May 2011.
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Enhanced grain surface effect on magnetic properties of nanometric La0.7Ca0.3MnO3 manganite : Evidence of surface spin freezing of manganite nanoparticles
Authors:
P. Dey,
T. K. Nath,
P. K. Manna,
S. M. Yusuf
Abstract:
We have investigated the effect of nanometric grain size on magnetic properties of single phase, nanocrystalline, granular La0.7Ca0.3MnO3 (LCMO) sample. We have considered core-shell structure of our LCMO nanoparticles, which can explain its magnetic properties. From the temperature dependence of field cooled (FC) and zero-field cooled (ZFC) dc magnetization (DCM), the magnetic properties could…
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We have investigated the effect of nanometric grain size on magnetic properties of single phase, nanocrystalline, granular La0.7Ca0.3MnO3 (LCMO) sample. We have considered core-shell structure of our LCMO nanoparticles, which can explain its magnetic properties. From the temperature dependence of field cooled (FC) and zero-field cooled (ZFC) dc magnetization (DCM), the magnetic properties could be distinguished into two regimes: a relatively high temperature regime T > 40 K where the broad maximum of ZFC curve (at T = Tmax) is associated with the blocking of core particle moments, whereas the sharp maximum (at T = TS) is related to the freezing of surface (shell) spins. The unusual shape of M (H) loop at T = 1.5 K, temperature dependent feature of coercive field and remanent magnetization give a strong support of surface spin freezing that are occurring at lower temperature regime (T < 40 K) in this LCMO nanoparticles. Additionally, waiting time (tw) dependence of ZFC relaxation measurements at T = 50 K show weak dependence of relaxation rate [S(t)] on tw and dM/dln(t) following a logarithmic variation on time. Both of these features strongly support the high temperature regime to be associated with the blocking of core moments. At T = 20 K, ZFC relaxation measurements indicates the existence of two different types of relaxation processes in the sample with S(t) attaining a maximum at the elapsed time very close to the wait time tw = 1000 sec, which is an unequivocal sign of glassy behavior. This age-dependent effect convincingly establish the surface spin freezing of our LCMO nanoparticles associated with a background of superparamagnetic (SPM) phase of core moments.
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Submitted 8 December, 2007;
originally announced December 2007.