Showing 1–19 of 19 results for author: Kaur, G

Effect of Vacancies on Hydrogen Mobility and Trapping in Elemental Fe and Cr: A DFT and kMC Study

Authors: Vallinathan K, Gurpreet Kaur, Sharat Chandra

Abstract: Hydrogen-vacancy interactions play an important role in governing hydrogen transport and embrittlement in body-centered cubic (BCC) metals. In this study, a multiscale approach combining density functional theory (DFT) and kinetic Monte Carlo (kMC) simulations is employed to investigate hydrogen behavior in BCC Fe and Cr. The DFT-calculated binding energies and Bader charge analysis indicate stron… ▽ More Hydrogen-vacancy interactions play an important role in governing hydrogen transport and embrittlement in body-centered cubic (BCC) metals. In this study, a multiscale approach combining density functional theory (DFT) and kinetic Monte Carlo (kMC) simulations is employed to investigate hydrogen behavior in BCC Fe and Cr. The DFT-calculated binding energies and Bader charge analysis indicate stronger hydrogen trapping in Cr than in Fe. Migration and detrapping energy barriers are determined using the climbing-image nudged elastic band method, showing that the detrapping energy generally decreases with increasing hydrogen occupancy. However, the sixth hydrogen atom in Fe exhibits a finite barrier, contrary to some previous reports. kMC simulations are then used to evaluate hydrogen diffusion over extended time and length scales. The results demonstrate that vacancy defects significantly reduce hydrogen mobility and increase the effective activation energy, with a more pronounced effect observed in Cr due to stronger trapping. The combined DFT-kMC framework provides detailed insight into the mechanisms of hydrogen trapping, detrapping, and diffusion in BCC metals, offering important implications for understanding hydrogen embrittlement in structural materials. △ Less

Submitted 27 May, 2026; originally announced May 2026.

Magnetoelastic honeycomb fragmentation in VI$_{3}$

Authors: Enlin Shen, Tiberiu I. Popescu, Nishwal Gora, Guratinder Kaur, Edmond Chan, Harry Lane, Jose A. Rodriguez-Rivera, Guangyong Xu, Peter M. Gehring, Russell A. Ewings, Andy N. Fitch, Chris Stock

Abstract: The discovery of ordered magnetism in two-dimensional van der Waals materials at the monolayer limit challenges the Mermin-Wagner theorem, which forbids spontaneous breaking of continuous symmetries in two dimensions at finite temperatures. The persistence of static magnetism in low-dimensions is fundamentally influenced by magnetic anisotropy and the local single-ion crystalline electric field. C… ▽ More The discovery of ordered magnetism in two-dimensional van der Waals materials at the monolayer limit challenges the Mermin-Wagner theorem, which forbids spontaneous breaking of continuous symmetries in two dimensions at finite temperatures. The persistence of static magnetism in low-dimensions is fundamentally influenced by magnetic anisotropy and the local single-ion crystalline electric field. Crucially, spin-orbit coupling connects the structural properties with spin degrees of freedom. We investigate the magnetic single-ion properties in the van der Waals magnet VI$_3$. Utilizing neutron and x-ray diffraction, we map out the symmetry breaking phase transitions and argue for a single structural transition at T$_S \sim$ 80 K, driven by an orbital degeneracy, followed by a ferromagnetic transition at a lower temperature, T$_C \sim$ 50 K. Through a comparative analysis of samples prepared under varying conditions, we suggest that lower temperature transitions reported near $\sim$ 30 K are not intrinsic to VI$_{3}$. A group theoretical analysis suggests a structural transition from rhombohedral $R\overline{3}$ to triclinic $P\overline{1}$ or $P1$. This transition is significant as it suggests the formation of two distinct crystallographyically inequivalent V$^{3+}$ sites, each with distinct spin-orbital properties. Neutron spectroscopy provides evidence for dominant magnetic exchange coupling only between symmetry-equivalent sites in the triclinc unit cell. We suggest this breaks up the low-temperature honeycomb VI$_3$ lattice into two interpenetrating approximately hexagonal planes resulting in a fragmentated honeycomb. Our findings highlight the critical role of magnetoelastic coupling in determining the magnetic and structural phases in two-dimensional van der Waals magnets. △ Less

Submitted 23 December, 2025; originally announced December 2025.

Comments: (16 pages, 10 figures, to be published in Physical Review B)

Anisotropic Band-Split Magnetism in Magnetostrictive CoFe$_2$O$_4$

Authors: Harry Lane, Guratinder Kaur, Masahiro Kawamata, Yusuke Nambu, Lukas Keller, Russell A. Ewings, David J. Voneshen, Travis J. Williams, Helen C. Walker, Dwight Viehland, Peter M. Gehring, Chris Stock

Abstract: Single crystal spinel CoFe$_2$O$_4$ exhibits the largest room-temperature saturation magnetostriction among non-rare-earth compounds and a high Curie temperature ($T_c \sim 780$ K), properties that are critical to a wide range of industrial and medical applications. Neutron spectroscopy reveals a large band splitting ($\sim$ 60 meV) between two ferrimagnetic magnon branches, which is driven by sit… ▽ More Single crystal spinel CoFe$_2$O$_4$ exhibits the largest room-temperature saturation magnetostriction among non-rare-earth compounds and a high Curie temperature ($T_c \sim 780$ K), properties that are critical to a wide range of industrial and medical applications. Neutron spectroscopy reveals a large band splitting ($\sim$ 60 meV) between two ferrimagnetic magnon branches, which is driven by site mixing between Co$^{2+}$ and Fe$^{3+}$ cations, and a significantly weaker magnetocrystalline anisotropy ($\sim$ 3 meV). Central to this behavior is the competition between extremely large mismatched molecular fields on the tetrahedral $A$-site and octahedral $B$-site sublattices and the single-ion anisotropy on the $B$-site. This creates a strong energetic anisotropy that locks the magnetic moment within each structural domain in place. As a result of these differing energy scales, switching structural domains is energetically favored over a global spin reorientation under applied magnetic fields, and this is what amplifies the magnetostrictive nature of CoFe$_2$O$_4$. △ Less

Submitted 17 December, 2025; originally announced December 2025.

Comments: (19 pages; 9 figures)

Journal ref: Adv.Funct.Mater. 2025, e16830

Exploring Low-Dimensional Magnetism in Cobalt Vanadates, ${A}$CoV$_{2}$O$_{7}$~(${A}$~=~Ca, Sr) : Crystal Growth and Magnetic Properties of Effective Spin-1/2 Zigzag Chains

Authors: Anzar Ali, Guratinder Kaur, Arvind Maurya, Isha, Kathrin Küster, Ulrich Starke, Pascal Puphal, Arvind Kumar Yogi, Masahiko Isobe

Abstract: We report the successful growth of high-quality single crystals of \ACVO, a quasi-one-dimensional zigzag chain compound containing Co$^{2+}$ ions, using the optical floating zone method. The crystal growth was stabilized under high-pressure argon-oxygen gas with slow growth rates, overcoming challenges associated with the incongruent melting behavior of this material. X-ray diffraction confirms th… ▽ More We report the successful growth of high-quality single crystals of \ACVO, a quasi-one-dimensional zigzag chain compound containing Co$^{2+}$ ions, using the optical floating zone method. The crystal growth was stabilized under high-pressure argon-oxygen gas with slow growth rates, overcoming challenges associated with the incongruent melting behavior of this material. X-ray diffraction confirms the zigzag arrangement of Co$^{2+}$ ions, forming a quasi-one-dimensional chain structure. Magnetic susceptibility and heat capacity measurements reveal an antiferromagnetic phase transition at the Néel temperature ($T_{\text{N}} \sim 3.5$ K) and negative Curie-Weiss temperatures, indicative of dominant antiferromagnetic interactions. The distorted CoO$_6$ octahedral geometry and strong spin-orbit coupling suggest that Co$^{2+}$ ions likely exhibit an effective $J = 1/2 $ Kramers doublet state. The results presented here demonstrate the potential of \ACVO\ as a platform for investigating low-dimensional magnetism and quantum magnetic phenomena. These insights shed light on the role of the ${A}$-site ion in tuning the magnetic interactions, which will foster future research into the field-induced behavior in these cobalt vanadates. △ Less

Submitted 24 June, 2025; originally announced June 2025.

Report number: APL Mater. 13, 071111 (2025)

Cluster Spin Glass State in Ba$_3$Sb$_{1+x}$Co$_{2-x}$O$_{9-δ}$: Cation Disorder and Mixed-Valence Co Dimers

Authors: Anzar Ali, Guratinder Kaur, Lukas Keller, Masahiko Isobe

Abstract: We investigate the structural, magnetic, and thermodynamic properties of \BSCO\ ($x$ = 0.04, $δ$ = 0.54), a hexagonal perovskite featuring face-sharing CoO$_6$ octahedra that forms Co dimers. DC and AC magnetization measurements reveal a frequency-dependent spin-freezing transition consistent with glassy dynamics. AC susceptibility fits best to the Vogel-Fulcher model, indicating collective freezi… ▽ More We investigate the structural, magnetic, and thermodynamic properties of \BSCO\ ($x$ = 0.04, $δ$ = 0.54), a hexagonal perovskite featuring face-sharing CoO$_6$ octahedra that forms Co dimers. DC and AC magnetization measurements reveal a frequency-dependent spin-freezing transition consistent with glassy dynamics. AC susceptibility fits best to the Vogel-Fulcher model, indicating collective freezing of interacting spin clusters. Isothermal magnetization follows the Langevin function, suggesting finite-sized magnetic clusters rather than isolated paramagnetic moments. Non-equilibrium dynamics, evidenced by thermoremanent magnetization and memory effects, further support a spin-glass-like state. Heat capacity shows no sharp anomalies, and neutron powder diffraction confirms the absence of magnetic Bragg peaks down to 1.5~K, ruling out long-range magnetic order. Rietveld refinement reveals significant Co/Sb intersite disorder ($\sim$~30\pct) and oxygen non-stoichiometry, introducing exchange randomness and frustration that drive the spin-glass-like behavior. Electrical resistivity exhibits Arrhenius-type temperature dependence with an activation energy of 0.173~eV, consistent with semiconducting behavior. Temperature-dependent X-ray diffraction shows no structural phase transitions, confirming that the spin-glass-like state is not lattice-driven. Our results establish \BSCO\ as a cluster spin-glass candidate, where Co dimers, disorder, and geometric frustration prevent long-range order, leading to slow spin dynamics. These findings highlight the role of cation disorder and oxygen vacancies in stabilizing unconventional magnetic states in cobalt-based hexagonal perovskites. △ Less

Submitted 24 June, 2025; originally announced June 2025.

Report number: Phys. Rev. B 112, 024409

Emergence of a Fluctuating Ground State in Y-kapellasite under Pressure

Authors: Dipranjan Chatterjee, Petr Doležal, Federico Abbruciati, Tobias Biesner, Katharina M. Zoch, Rustem Khasanov, Shams Sohel Islam, Guratinder Kaur, Seulki Roh, Francesco Capitani, Joao Elias F. S. Rodrigues, Gaston Garbarino, Cornelius Krellner, Philippe Mendels, Edwin Kermarrec, Martin Dressel, Björn Wehinger, Andrej Pustogow, Fabrice Bert, Pascal Puphal

Abstract: Y-kapellasite (Y$_3$Cu$_9$(OH)$_{19}$Cl$_8$), which hosts an original anisotropic kagome sublattice, is a promising candidate for studying elusive and complex correlated physics. It exhibits a theoretically predicted in-plane $(1/3, 1/3)$ magnetic order [1] but its magnetic interaction values place it close to a phase boundary to a spin liquid state [2]. Our $μ$SR measurements under hydrostatic pr… ▽ More Y-kapellasite (Y$_3$Cu$_9$(OH)$_{19}$Cl$_8$), which hosts an original anisotropic kagome sublattice, is a promising candidate for studying elusive and complex correlated physics. It exhibits a theoretically predicted in-plane $(1/3, 1/3)$ magnetic order [1] but its magnetic interaction values place it close to a phase boundary to a spin liquid state [2]. Our $μ$SR measurements under hydrostatic pressure demonstrate the complete suppression of static magnetism in favor of a fully dynamical ground state at $2.3$~GPa. Complementary high-pressure x-ray and optical phonon measurements reveal a gradual reduction of the kagome anisotropy, enhancing magnetic frustration without structural transitions. Our results establish Y-kapellasite as a rare clean kagome model in which long-range order is suppressed by pressure-tuned frustration, the first fingerprint for the realization of a quantum spin liquid without strong disorder. △ Less

Submitted 31 March, 2026; v1 submitted 13 February, 2025; originally announced February 2025.

Comments: 6 pages, 4 figures

Thermal Stability and Depinning Currents of Domain Wall-Based Artificial Synapses

Authors: Guntas Kaur, Tanmoy Pramanik

Abstract: Micromagnetic modeling is employed to optimize the design of artificial synapse devices based on the spin-orbit-torque (SOT) driven domain wall (DW) motion along a nanotrack with triangular notches. Key attributes, such as the thermal stability of the pinned DW and depinning currents, are obtained for varied nanotrack geometry and pinning strength. Depinning probability as a function of SOT curren… ▽ More Micromagnetic modeling is employed to optimize the design of artificial synapse devices based on the spin-orbit-torque (SOT) driven domain wall (DW) motion along a nanotrack with triangular notches. Key attributes, such as the thermal stability of the pinned DW and depinning currents, are obtained for varied nanotrack geometry and pinning strength. Depinning probability as a function of SOT current density and pulse width is studied using finite temperature micromagnetic simulations for varying pinning potential. Results show that wider notches provide better thermal stability - depinning current trade-off. On the other hand, narrow notches exhibit less variation in the depinning times at finite temperatures. It is observed that the DW position can be set precisely to any desired location by the SOT current pulse if the thermal stability is sufficiently high. It is also observed that the meta-plastic functionality can be obtained by adding notches of progressively higher depinning currents along the rectangular nanotrack. △ Less

Submitted 25 January, 2025; originally announced January 2025.

Comments: 12 pages, 6 figures

Emergence of low temperature glassy dynamics in Ru substituted non magnetic insulator CaHfO3

Authors: Gurpreet Kaur, K. Mukherjee

Abstract: Non magnetic insulators/semiconductors with induced magnetism introduced via transition metal substitution are one of the promising materials in the field of spintronic, magnetoelectronics and magneto optical devices. In this context, here, we focus on magnetism induced in a non magnetic insulator CaHfO3, by the substitution of 4d element Ru, at Hf site. Structural investigations indicate that sub… ▽ More Non magnetic insulators/semiconductors with induced magnetism introduced via transition metal substitution are one of the promising materials in the field of spintronic, magnetoelectronics and magneto optical devices. In this context, here, we focus on magnetism induced in a non magnetic insulator CaHfO3, by the substitution of 4d element Ru, at Hf site. Structural investigations indicate that substitution of Ru4+ (up to 50%) does not affect the original crystal structure of the parent compound. Magnetic studies divulge a crossover from a diamagnetic to paramagnetic state with 20% Ru substitution. Further replacement of Hf results in a glassy magnetic state in CaHf1-xRuxO3 (0.3 < x < 0.5). The nature of the low temperature glassiness (below 20 K) in these compositions is confirmed through Vogel Fulcher and Power law, along with, magnetic memory effect and relaxation dynamics. The observed glassiness is explained through the phenomenological hierarchical model. Our studies indicate that the presence of competing short range interactions among randomly arranged Ru cations in non magnetic insulator CaHfO3 are responsible for the observed low temperature magnetic state in this series with compositions > 0.25. △ Less

Submitted 2 August, 2022; originally announced August 2022.

Comments: Accepted in J. Phys. Condens. Matter (2022)

Journal ref: J. Phys. Condens. Matter 34, 415802 (2022)

Ab initio Molecular Dynamics Simulation of Threshold Displacement Energies and Defect Formation Energies in Y4Zr3O12

Authors: Sruthi Mohan, Gurpreet Kaur, C. David, B. K. Panigrahi, G. Amarendra

Abstract: Ab initio molecular dynamics simulations using VASP was employed to calculate threshold displacement energies and defect formation energies of Y4Zr3O12 δ-phase, which is the most commonly found phase in newly developed Zr and Al-containing ODS steels. The Threshold displacement energy (Ed) values are determined to be 28 eV for Zr3a primary knock-on atom along [111] direction, 40 eV for Zr18f atoms… ▽ More Ab initio molecular dynamics simulations using VASP was employed to calculate threshold displacement energies and defect formation energies of Y4Zr3O12 δ-phase, which is the most commonly found phase in newly developed Zr and Al-containing ODS steels. The Threshold displacement energy (Ed) values are determined to be 28 eV for Zr3a primary knock-on atom along [111] direction, 40 eV for Zr18f atoms along [111] direction and 50 eV for Y recoils along [110] direction. Minimum Ed values for O and O' atoms are 13 eV and 16 eV respectively. The displacement energies of anions are much smaller compared to cations, thus suggesting that anion disorder is more probable than cation disorder. All directions except the direction in which inherent structural vacancies are aligned, cations tend to occupy another cation site. The threshold displacement energies are larger than that of Y2Ti2O7, the conventional precipitates in Ti containing ODS steels. Due to the partial occupancy of Y and Zr in the 18f position, the antisite formation energy is negligibly small, and it may help the structure to withstand more disorder upon irradiation. These results convey that Zr/Al ODS alloys, which have better corrosion resistance properties compared to the conventional Ti-ODS alloys, may also possess superior radiation resistance. △ Less

Submitted 31 May, 2021; originally announced May 2021.

Effect of Zr and Al Addition on Nanocluster Formation in Oxide Dispersion Strenghthened Steel-an ab initio Study

Authors: Sruthi Mohan, Gurpreet Kaur, B. K. Panigrahi, C. David, G. Amarendra

Abstract: Conventional Oxide dispersion strengthened steels are characterized by thermally stable, high density of Y-Ti-O nanoclusters, which are responsible for their high creep strength. Ti plays a major role in obtaining a high density of ultrafine particles of optimum size range of 2-10 nm. In Al-containing ODS steels developed for corrosion resistance, Y-Al-O clusters formed are of size range 20 -100 n… ▽ More Conventional Oxide dispersion strengthened steels are characterized by thermally stable, high density of Y-Ti-O nanoclusters, which are responsible for their high creep strength. Ti plays a major role in obtaining a high density of ultrafine particles of optimum size range of 2-10 nm. In Al-containing ODS steels developed for corrosion resistance, Y-Al-O clusters formed are of size range 20 -100 nm, and Ti fails in making dispersions finer in the presence of Al. Usage of similar alloying elements like Zr in place of Ti is widely considered. In this study, binding energies of different stages of Y-Zr-O-Vacancy and Y-Al-O-Vacancy complexes in the bcc Iron matrix are studied by first-principle calculations. It is shown that in all the stages of formation, Y-Zr-O-Vacancy clusters have higher binding energy than Y-Al-O-Vacancy clusters and hence in ferritic steel containing both Zr and Al, Y-Zr-O-Vacancy clusters are more stable and more favored to nucleate than Y-Al-O-Vacancy clusters. The bonding nature in each stage is analyzed using charge density difference plots for the plausible reason for higher stability of Y-Zr-O-Vacancy clusters. △ Less

Submitted 31 May, 2021; originally announced May 2021.

Experimental validation of density functional theory calculations on the Zr/Al oxide nanocluster formation in bcc Fe

Authors: Sruthi Mohan, Gurpreet Kaur, C. David, R. Vijay, G. Amarendra

Abstract: Ab initio simulations carried out in different atomic cluster configurations in bcc Fe matrix containing Zr and Al suggest energetic favorability of Y-Zr-O phase nucleation, preferably with trigonal Y4Zr3O12 structure. Subsequently, the HRTEM investigation of the as-prepared Fe - 14 Cr-0.3 Y2O3 - 0.6 Zr - 4Al oxide dispersion strengthened (ODS) alloy shows 78% of precipitates with Y4Zr3O12 structu… ▽ More Ab initio simulations carried out in different atomic cluster configurations in bcc Fe matrix containing Zr and Al suggest energetic favorability of Y-Zr-O phase nucleation, preferably with trigonal Y4Zr3O12 structure. Subsequently, the HRTEM investigation of the as-prepared Fe - 14 Cr-0.3 Y2O3 - 0.6 Zr - 4Al oxide dispersion strengthened (ODS) alloy shows 78% of precipitates with Y4Zr3O12 structure, thereby confirming the predictive power of ab initio simulations on the secondary formation in multi-component alloys. △ Less

Submitted 2 March, 2022; v1 submitted 27 May, 2021; originally announced May 2021.

Comments: further data analysis

Correlation between anion defects and ion beam induced luminescence in Y4Zr3O12

Authors: Sruthi Mohan, Gurpreet Kaur, Sachin Srivastava, P. Magudapathy, C. David, G. Amarendra

Abstract: Potential applications of Zr/Al ODS alloys vests on the irradiation stability of the Y4Zr3O12 dispersoids. Fundamental studies to identify the type of defects are important in order to recognize pathways for damage alleviation. In this context, studies relating to identification of point defects and their clusters by in-situ ionoluminescence spectroscopy were taken up. The ionoluminescence spectru… ▽ More Potential applications of Zr/Al ODS alloys vests on the irradiation stability of the Y4Zr3O12 dispersoids. Fundamental studies to identify the type of defects are important in order to recognize pathways for damage alleviation. In this context, studies relating to identification of point defects and their clusters by in-situ ionoluminescence spectroscopy were taken up. The ionoluminescence spectrum acquired during 100 keV He+ ion irradiation shows two prominent bands, at 330 nm and 415 nm. Using density functional theory calculations with HSE06 hybrid exchange correlation functional, the luminescent bands have been identified to be arising due to native and irradiation induced oxygen vacancy defects in charged and neutral configurations. △ Less

Submitted 22 May, 2021; originally announced May 2021.

Comments: 10 pages, 5 figures

Fractional antiferromagnetic skyrmion lattice induced by anisotropic couplings

Authors: Shang Gao, H. D. Rosales, F. A. Gómez Albarracín, Vladimir Tsurkan, Guratinder Kaur, Tom Fennell, Paul Steffens, Martin Boehm, Petr Čermák, Astrid Schneidewind, Eric Ressouche, Daniel C. Cabra, Christian Rüegg, Oksana Zaharko

Abstract: Magnetic skyrmions are topological solitons with a nanoscale winding spin texture that hold promise for spintronics applications. Until now, skyrmions have been observed in a variety of magnets that exhibit nearly parallel alignment for the neighbouring spins, but theoretically, skyrmions with anti-parallel neighbouring spins are also possible. The latter, antiferromagnetic skyrmions, may allow mo… ▽ More Magnetic skyrmions are topological solitons with a nanoscale winding spin texture that hold promise for spintronics applications. Until now, skyrmions have been observed in a variety of magnets that exhibit nearly parallel alignment for the neighbouring spins, but theoretically, skyrmions with anti-parallel neighbouring spins are also possible. The latter, antiferromagnetic skyrmions, may allow more flexible control compared to the conventional ferromagnetic skyrmions. Here, by combining neutron scattering and Monte Carlo simulations, we show that a fractional antiferromagnetic skyrmion lattice with an incipient meron character is stabilized in MnSc$_2$S$_4$ through anisotropic couplings. Our work demonstrates that the theoretically proposed antiferromagnetic skyrmions can be stabilized in real materials and represents an important step towards implementing the antiferromagnetic-skyrmion based spintronic devices. △ Less

Submitted 23 September, 2020; originally announced September 2020.

Comments: 14 pages, 11 figures, submitted version with necessary edits

Journal ref: Nature 586, 37 (2020)

Ultrafast Insight into High energy (C, D) Excitons in Few Layer WS2

Authors: Tanmay Goswami, Himanshu Bhatt, K. Justice Babu, Gurpreet Kaur, Nandan Ghorai, Hirendra N. Ghosh

Abstract: High energy (C, D) excitons possess remarkable influence over the optical properties of layered transition metal dichalcogenides (TMDCs) and comprehensive understanding of these may have revolutionary effect on 2D opto-electronic devices. Herein, we employed transient absorption spectroscopy to monitor the underlying photo-physical processes involved with C, D excitons in few layer WS2. We observe… ▽ More High energy (C, D) excitons possess remarkable influence over the optical properties of layered transition metal dichalcogenides (TMDCs) and comprehensive understanding of these may have revolutionary effect on 2D opto-electronic devices. Herein, we employed transient absorption spectroscopy to monitor the underlying photo-physical processes involved with C, D excitons in few layer WS2. We observed a strong inter-valley coupling across the momentum space. C, D dynamics were significantly slower as compared to canonical A, B excitons, as a consequence of the indirect Lambda-Gamma relaxation in C, D, unlike K-K direct combination in A, B. Optical behaviour of D excitons was found to be more like A, B, contrary to C, which enjoy unique band nesting effects. Also, C excitons do not hold in any specific position of the momentum space, rather depends upon the photon energy. All these excitons immensely influence each other irrespective of the excitation energy. △ Less

Submitted 11 September, 2020; originally announced September 2020.

Magnetocaloric effect and spin-phonon correlations in RFe0.5Cr0.5O3 (R = Er and Yb) compounds

Authors: Kavita Yadav, Gurpreet Kaur, Mohit K. Sharma, K. Mukherjee

Abstract: We report the results of our investigation of the physical properties of mixed metal oxides RFe0.5Cr0.5O3 (R = Er and Yb). ErFe0.5Cr0.5O3 undergoes an antiferromagnetic ordering around 270 K followed by spin reorientation (SR) transitions around 150 and 8 K respectively. In contrast, in YbFe0.5Cr0.5O3 a single SR transition is noted at 36 K, below the AFM ordering temperature of 280 K. In ErFe0.5C… ▽ More We report the results of our investigation of the physical properties of mixed metal oxides RFe0.5Cr0.5O3 (R = Er and Yb). ErFe0.5Cr0.5O3 undergoes an antiferromagnetic ordering around 270 K followed by spin reorientation (SR) transitions around 150 and 8 K respectively. In contrast, in YbFe0.5Cr0.5O3 a single SR transition is noted at 36 K, below the AFM ordering temperature of 280 K. In ErFe0.5Cr0.5O3, a significant value of magnetic entropy change (ΔSM) ~ -12.4 J/kg-K is noted near the 2nd SR transition, however, this value is suppressed in YbFe0.5Cr0.5O3. Temperature dependent dielectric permittivity of ErFe0.5Cr0.5O3 and YbFe0.5Cr0.5O3 at different frequencies, reveal the presence of Debye-like relaxation behaviour in both compounds, which can be due to the effect of charge carrier hopping between localized states of Fe and Cr ions. Temperature dependent Raman scattering studies divulge that spin-phonon coupling plays a crucial role in defining the physical properties of these compounds. △ Less

Submitted 1 June, 2020; originally announced June 2020.

Journal ref: Phys. Letts. A 384, 126638 (2020)

Nature of glassy magnetic state in magnetocaloric materials Dy5Pd2-xNix (x = 0 and 1) and universal scaling analysis of R5Pd2 (R = Tb, Dy and Er)

Authors: Mohit K. Sharma, Gurpreet Kaur, K. Mukherjee

Abstract: We report a systematic investigation of the magnetic and magnetocaloric properties of Dy5Pd2 and Dy5PdNi. Our study on these compounds gave evidence that they exhibit complex magnetic behaviour along with the presence of glass-like magnetic phase. Furthermore, in these compounds both second order and first order phase transitions were present, which were validated through Arrott plots and Landau p… ▽ More We report a systematic investigation of the magnetic and magnetocaloric properties of Dy5Pd2 and Dy5PdNi. Our study on these compounds gave evidence that they exhibit complex magnetic behaviour along with the presence of glass-like magnetic phase. Furthermore, in these compounds both second order and first order phase transitions were present, which were validated through Arrott plots and Landau parameter analysis. AC susceptibility along with time dependent magnetisation study has confirmed the presence of double cluster glass-like freezing in both Dy5Pd2 and Dy5PdNi. These compounds show significant value of isothermal entropy change and relative cooling power and these values increased with Ni substitution. Beside conventional magnetocaloric effect, inverse magnetocaloric effect was noted in these compounds, which might arise due to the presence of complex non-equilibrium magnetic state. Along with these compounds a universal characteristic curve involving two other members of R5Pd2 family i.e. Er5Pd2 and Tb5Pd2 was constructed. The master curve reaffirmed the presence of both second and first order magnetic phase transition in such compounds which were in analogy to our results of Arrott plots and Landau parameter analysis. Additionally, magnetic entropy change followed the power law and the obtained exponent values indicated the presence of mixed magnetic interactions in these compounds. △ Less

Submitted 10 September, 2018; originally announced September 2018.

Journal ref: J. Alloys and Compd. 782, 10 (2019

Specially designed B4C/SnO2 nanocomposite for photocatalysis: traditional ceramic with unique properties

Authors: Paviter Singh, Gurpreet Kaur, Kulwinder Singh, Bikramjeet Singh, Manpreet Kaur, Manjot Kaur, Unni Krishnan, Manjeet Kumar, Rajni Bala, Akshay Kumar

Abstract: Boron carbide: A traditional ceramic material shows unique properties when explored in nano-range. Specially designed boron based nanocomposite has been synthesized by reflux method. The addition of SnO2 in base matrix increase the defect states in boron carbide and shows unique catalytic properties. The calculated texture coefficient and Nelson Riley factor shows that the synthesized nanocomposit… ▽ More Boron carbide: A traditional ceramic material shows unique properties when explored in nano-range. Specially designed boron based nanocomposite has been synthesized by reflux method. The addition of SnO2 in base matrix increase the defect states in boron carbide and shows unique catalytic properties. The calculated texture coefficient and Nelson Riley factor shows that the synthesized nanocomposite have very high defect states. Also this composite is explored for the first time for catalysis degradation of industrial used dyes. The industrial pollutants such as Novacron red and methylene blue dye degradation analysis reveal that the composite is an efficient catalyst. Degradation study shows that 1 g/L catalyst concentration of B4C/SnO2 degrade Novacron red Huntsman dye upto 97.38% approximately in 20 minutes under sunlight irradiation time. This water insoluble catalyst can be recovered and reused. △ Less

Submitted 15 November, 2017; originally announced November 2017.

Decay of spin coherences in one-dimensional spin systems

Authors: Gurneet Kaur, Ashok Ajoy, Paola Cappellaro

Abstract: Strategies to protect multi-qubit states against decoherence are difficult to formulate because of their complex many-body dynamics. A better knowledge of the decay dynamics would help in the construction of decoupling control schemes. Here we use solid-state nuclear magnetic resonance techniques to experimentally investigate the decay of coherent multi-spin states in linear spin chains. Leveragin… ▽ More Strategies to protect multi-qubit states against decoherence are difficult to formulate because of their complex many-body dynamics. A better knowledge of the decay dynamics would help in the construction of decoupling control schemes. Here we use solid-state nuclear magnetic resonance techniques to experimentally investigate the decay of coherent multi-spin states in linear spin chains. Leveraging on the quasi-one-dimensional geometry of Fluorapatite crystal spin systems, we can gain a deeper insight on the multi-spin states created by the coherent evolution, and their subsequent decay, than it is possible in 3D systems. We are then able to formulate an analytical model that captures the key features of the decay. We can thus compare the decoherence behavior for different initial states of the spin chain and link their decay rate to the state characteristics, in particular their coherence and long-range correlation among spins. Our experimental and theoretical study shows that the spin chains undergo a rich dynamics, with a slower decay rate than for the 3D case, and thus might be more amenable to decoupling techniques. △ Less

Submitted 11 June, 2013; originally announced June 2013.

Journal ref: New J. Phys. 15, 093035 (2013)

Initialization and Readout of Spin Chains for Quantum Information Transport

Authors: Gurneet Kaur, Paola Cappellaro

Abstract: Linear chains of spins acting as quantum wires are a promising approach to achieve scalable quantum information processors. Nuclear spins in apatite crystals provide an ideal test-bed for the experimental study of quantum information transport, as they closely emulate a one-dimensional spin chain. Nuclear Magnetic Resonance techniques can be used to drive the spin chain dynamics and probe the acco… ▽ More Linear chains of spins acting as quantum wires are a promising approach to achieve scalable quantum information processors. Nuclear spins in apatite crystals provide an ideal test-bed for the experimental study of quantum information transport, as they closely emulate a one-dimensional spin chain. Nuclear Magnetic Resonance techniques can be used to drive the spin chain dynamics and probe the accompanying transport mechanisms. Here we demonstrate initialization and readout capabilities in these spin chains, even in the absence of single-spin addressability. These control schemes enable preparing desired states for quantum information transport and probing their evolution under the transport Hamiltonian. We further optimize the control schemes by a detailed analysis of $^{19}$F NMR lineshape. △ Less

Submitted 2 December, 2011; originally announced December 2011.