-
Hydration-Controlled Layer Stacking in (NH$_3$)$_2$Cu$_5$(SeO$_3$)$_2$(OH)$_6$(H$_2$O)$_{2+x}$ ($x$ = 0, 1, and 3)
Authors:
Priya R. Baral,
Christian Jandl,
Pauline Pradal,
Johann Roos,
Wenhua Bi,
Arnaud Magrez
Abstract:
Hydration and dehydration are powerful yet underexplored variables for controlling the architecture of layered inorganic materials, because intercalated water can modify interlayer separation, hydrogen-bonding networks, and layer stacking. Here, we report the reflux synthesis of a new family of hydrated layered copper selenites, (NH$_3$)$_2$Cu$_5$(SeO$_3$)$_2$(OH)$_6$(H$_2$O)$_{2+x}$ ($x$ = 0, 1,…
▽ More
Hydration and dehydration are powerful yet underexplored variables for controlling the architecture of layered inorganic materials, because intercalated water can modify interlayer separation, hydrogen-bonding networks, and layer stacking. Here, we report the reflux synthesis of a new family of hydrated layered copper selenites, (NH$_3$)$_2$Cu$_5$(SeO$_3$)$_2$(OH)$_6$(H$_2$O)$_{2+x}$ ($x$ = 0, 1, and 3). From the crystal structures determined using electron diffraction and single crystal X-ray diffraction, we deduce that all three compounds share an identical layer built from Cu(OH)$_4$ squares and Cu-centered square pyramids forming distorted kagomé-like Cu$^{2+}$ network. While the intralayer atomic arrangement is preserved across the series, the degree of hydration governs both the interlayer separation and the stacking sequence. These compounds therefore provide a rare platform relevant to the design of hydration-responsive materials for sensing, ion transport, separations, actuation, and energy-related applications. The preservation of distorted kagomé-like Cu$^{2+}$ layers across hydration states further suggests potential interest for examining how interlayer water and stacking sequence affect low-dimensional magnetic coupling. Under reflux conditions, these phases are also shown to act as reactive intermediates in the formation of Cu$_2$OSeO$_3$, establishing them as tunable precursors for copper oxoselenite synthesis.
△ Less
Submitted 30 July, 2026;
originally announced July 2026.
-
Collinear ferromagnetism with reduced moment length in kagome magnet Nd3Ru4Al12
Authors:
Yuki Ishihara,
Ryota Nakano,
Rinsuke Yamada,
Takuya Nomoto,
Priya R. Baral,
Moritz M. Hirschmann,
Kamini Gautam,
Kamil K. Kolincio,
Akiko Kikkawa,
Seno Aji,
Hiraku Saitoh,
Masaaki Matsuda,
Yasujiro Taguchi,
Taka-hisa Arima,
Yoshinori Tokura,
Taro Nakajima,
Max Hirschberger
Abstract:
We determine the magnetic ground state of the kagome lattice magnet Nd3Ru4Al12 by single-crystal neutron diffraction, supported by experiments with polarized neutrons. We identify this material as a collinear ferromagnet ("hex-FM") with uniform moment length mc = 2.1 μB/Nd and ordering vector Q = 0, in contrast to a previous, seminal report that proposed unequal moment lengths on two Nd sites, her…
▽ More
We determine the magnetic ground state of the kagome lattice magnet Nd3Ru4Al12 by single-crystal neutron diffraction, supported by experiments with polarized neutrons. We identify this material as a collinear ferromagnet ("hex-FM") with uniform moment length mc = 2.1 μB/Nd and ordering vector Q = 0, in contrast to a previous, seminal report that proposed unequal moment lengths on two Nd sites, here called the "ortho-FM" state. Our analysis of the flipping ratio in polarized neutron scattering is consistent with the hex-FM state. The results provide a microscopic basis for understanding the large fluctuation-induced Hall and Nernst responses near TC = 41 K, as previously reported for Nd3Ru4Al12.
△ Less
Submitted 2 June, 2026; v1 submitted 2 May, 2026;
originally announced May 2026.
-
Bond-density-wave orders induced by geometric frustration in the kagome metal CeRu3Si2
Authors:
Ryo Misawa,
Shunsuke Kitou,
Rinsuke Yamada,
Xiaolong Feng,
Ryota Nakano,
Priya Ranjan Baral,
Yuiga Nakamura,
Leslie M. Schoop,
Yukitoshi Motome,
Taka-hisa Arima,
Xiuzhen Yu,
Max Hirschberger
Abstract:
Geometric frustration gives rise to vast manifolds of degenerate ground states and competing orders in spin and charge systems. Typically, classical ground states are governed by a local ``zero-sum constraint" that relieves frustrated antiferromagnetic interactions or Coulomb repulsion. To date, the paradigm of geometric frustration has yielded a rich landscape of emergent phases, from spin ices a…
▽ More
Geometric frustration gives rise to vast manifolds of degenerate ground states and competing orders in spin and charge systems. Typically, classical ground states are governed by a local ``zero-sum constraint" that relieves frustrated antiferromagnetic interactions or Coulomb repulsion. To date, the paradigm of geometric frustration has yielded a rich landscape of emergent phases, from spin ices and quantum spin liquids to charge glasses. However, an analogous phase rooted in chemical bonding has yet to be firmly demonstrated. Here we report the discovery of bond-density-wave orders induced by geometric frustration in the kagome metal CeRu$_3$Si$_2$ above room temperature. Through synchrotron X-ray diffraction, real-space transmission electron microscopy, and model calculations, we observe two distinct long-period superlattices with harmonic and anharmonic structural modulations. Crucially, interlayer bonds between kagome planes modulate in a sublattice-selective manner to fulfill the zero-sum constraint on the kagome lattice. We demonstrate the potential of kagome metals to host complex bond-ordered states constrained by geometric frustration and establish chemical bonding as a distinct pathway to frustration physics in quantum materials even above room temperature.
△ Less
Submitted 2 April, 2026;
originally announced April 2026.
-
Stripe antiferromagnetism in van der Waals metal HoTe3 decoupled from charge density wave order
Authors:
Weiyi Yun,
Ryota Nakano,
Ryo Misawa,
Rinsuke Yamada,
Shun Akatsuka,
Yoshichika Onuki,
Priya Ranjan Baral,
Hiraku Saitoh,
Ryoji Kiyanagi,
Takashi Ohhara,
Taro Nakajima,
Taka-hisa Arima,
Max Hirschberger
Abstract:
The $R\mathrm{Te}_3$ ($R = \text{rare earth}$) family of layered van der Waals (vdW) compounds hosts coexisting magnetic and charge density wave (CDW) orders, yet the interplay between these degrees of freedom remains little explored. Combining polarized and unpolarized neutron diffraction on single-crystal $\mathrm{HoTe}_3$, we identify two distinct antiferromagnetic (AFM) phases, both exhibiting…
▽ More
The $R\mathrm{Te}_3$ ($R = \text{rare earth}$) family of layered van der Waals (vdW) compounds hosts coexisting magnetic and charge density wave (CDW) orders, yet the interplay between these degrees of freedom remains little explored. Combining polarized and unpolarized neutron diffraction on single-crystal $\mathrm{HoTe}_3$, we identify two distinct antiferromagnetic (AFM) phases, both exhibiting a collinear $\uparrow\uparrow\downarrow\downarrow$ motif within individual vdW layers. The two phases are distinguished by the vdW stacking of magnetic layers: ferromagnetic (FM) stacking in the higher-temperature AFM-II phase, here termed ``vertical-stripe'', and AFM stacking in the AFM-I ground state, here termed ``tilted-stripe''; the two phases have propagation vectors $\boldsymbol{q}_{\mathrm{m2}} = (0.48, 0, 0)$ and $\boldsymbol{q}_{\mathrm{m1}} = (0.5, 0.5, 0)$, respectively. In contrast to the CDW-driven exotic magnetism in $\mathrm{DyTe}_3$, $\mathrm{TbTe}_3$, and $\mathrm{GdTe}_3$, we find no evidence for coupling between magnetism and CDW in $\mathrm{HoTe}_3$. The relative alignment between AFM and CDW propagation vectors, as well as single-ion anisotropy, are likely essential for generating coupled spin/charge orders in layered vdW systems.
△ Less
Submitted 23 March, 2026; v1 submitted 18 February, 2026;
originally announced February 2026.
-
Single-ion anisotropy-stabilized short-period helimagnetism in frustrated chiral Co$_5$TeO$_8$
Authors:
Priya R. Baral,
Ravi Yadav,
Victor Ukleev,
Thomas LaGrange,
Ivica Živković,
Wen Hua Bi,
Marek Bartkowiak,
Robert Cubitt,
Nina-Juliane Steinke,
Vladimir Pomjakushin,
Yurii Skourski,
Henrik M. Rønnow,
Oleg V. Yazyev,
Arnaud Magrez,
Jonathan S. White
Abstract:
Chiral spin textures in magnetic insulators promise magneto-electric (ME) spintronics with orders-of-magnitude lower power consumption than metallic systems. However, realizing the short magnetic periods required for high-density device integration remains difficult, as conventional Dzyaloshinskii-Moriya interaction (DMI)-based mechanisms typically constrain spiral periods to tens of nanometers. W…
▽ More
Chiral spin textures in magnetic insulators promise magneto-electric (ME) spintronics with orders-of-magnitude lower power consumption than metallic systems. However, realizing the short magnetic periods required for high-density device integration remains difficult, as conventional Dzyaloshinskii-Moriya interaction (DMI)-based mechanisms typically constrain spiral periods to tens of nanometers. While theory predicts that strong single-ion anisotropy (SIA) on frustrated lattices can stabilize complex non-coplanar textures, the potential for using this mechanism to engineer such compact textures remains largely unexplored. Here we report that a cubic chiral insulator Co$_5$TeO$_8$ provides an experimental example of this paradigm. Comprehensive neutron scattering and magnetometry reveal helimagnetic spirals with continuously tunable pitch of 5.7-10 nm embedded in a complex phase diagram spanning eight distinct phases. Capacitance anomalies throughout the phase diagram indicate magneto-electric coupling, pointing to the possibility of future $E$-field control of these textures. The temperature- and field-dependence of the helical wavevector strongly support a scenario in which site-dependent SIA provides the leading contribution to the selection of the helical period from a frustration-induced degenerate manifold. Consistent with this interpretation, $ab\,initio$ calculations place SIA approximately an order of magnitude above DMI, distinct from conventional helimagnets. Co$_5$TeO$_8$ thus offers an experimental realization of sub-10 nm helimagnetism and motivates a design principle for anisotropy-engineered correlated insulators.
△ Less
Submitted 4 June, 2026; v1 submitted 17 December, 2025;
originally announced December 2025.
-
Cu2OSeO3 Turns Trigonal with Structural Transformation and Implications for Skyrmions
Authors:
Alla Arakcheeva,
Priya Ranjan Baral,
Wen Hua Bi,
Christian Jandl,
Oleg Janson,
Arnaud Magrez
Abstract:
The formation and characteristics of magnetic skyrmions are strongly governed by the symmetry of the underlying crystal structure. In this study, we report the discovery of a new trigonal polymorph of Cu2OSeO3, observed exclusively in nanoparticles. Electron diffraction and density functional theory calculations confirm its R3m space group, sharing C3v symmetry with Néel-type skyrmion hosts. This…
▽ More
The formation and characteristics of magnetic skyrmions are strongly governed by the symmetry of the underlying crystal structure. In this study, we report the discovery of a new trigonal polymorph of Cu2OSeO3, observed exclusively in nanoparticles. Electron diffraction and density functional theory calculations confirm its R3m space group, sharing C3v symmetry with Néel-type skyrmion hosts. This polymorph is likely stabilized by surface effects, suggesting that size-induced structural changes may drive a transformation from Bloch-type to Neel-type skyrmions in Cu2OSeO3. This hypothesis is consistent with prior unexplained observations of Neel-type skyrmions at the surfaces of bulk crystals, which may result from surface-specific structural distortions. Overall, these findings provide insights into the interplay between size, structure, and magnetism, opening pathways for controlling skyrmionic properties in nanoscale systems.
△ Less
Submitted 11 August, 2025;
originally announced August 2025.
-
Advanced SQUID-on-lever scanning probe for high-sensitivity magnetic microscopy with sub-100-nm spatial resolution
Authors:
Timur Weber,
Daniel Jetter,
Jan Ullmann,
Simon A. Koch,
Simon F. Pfander,
Katharina Kress,
Andriani Vervelaki,
Boris Gross,
Oliver Kieler,
Ute Drechsler,
Priya R. Baral,
Arnaud Magrez,
Reinhold Kleiner,
Armin W. Knoll,
Martino Poggio,
Dieter Koelle
Abstract:
Superconducting quantum interference devices (SQUIDs) are exceptionally sensitive magnetometers capable of detecting weak magnetic fields. Miniaturizing these devices and integrating them onto scanning probes enables high-resolution imaging at low-temperature. Here, we fabricate nanometer-scale niobium SQUIDs with inner-loop sizes down to 10 nm at the apex of individual planar silicon cantilevers…
▽ More
Superconducting quantum interference devices (SQUIDs) are exceptionally sensitive magnetometers capable of detecting weak magnetic fields. Miniaturizing these devices and integrating them onto scanning probes enables high-resolution imaging at low-temperature. Here, we fabricate nanometer-scale niobium SQUIDs with inner-loop sizes down to 10 nm at the apex of individual planar silicon cantilevers via a combination of wafer-scale optical lithography and focused-ion-beam (FIB) milling. These robust SQUID-on-lever probes overcome many of the limitations of existing devices, achieving spatial resolution better than 100 nm, magnetic flux sensitivity of $0.3~μΦ_0/\sqrt{\rm{Hz}}$, and operation in magnetic fields up to about 0.5 T at 4.2 K. Nanopatterning via Ne- or He-FIB allows for the incorporation of a modulation line for coupling magnetic flux into the SQUID or a third Josephson junction for shifting its phase. Such advanced functionality, combined with high spatial resolution, large magnetic field range, and the ease of use of a cantilever-based scanning probe, extends the applicability of scanning SQUID microscopy to a wide range of magnetic, normal conducting, superconducting, and quantum Hall systems. We demonstrate magnetic imaging of skyrmions at the surface of bulk Cu$_2$OSeO$_3$. Analysis of the point spread function determined from imaging a single skyrmion yields a full-width-half-maximum of 87 nm. Moreover, we image modulated magnetization patterns with a period of 65 nm.
△ Less
Submitted 3 August, 2025;
originally announced August 2025.
-
A Surface-confined Spiral State With the Double Period in the Cubic Chiral Helimagnet Cu$_2$OSeO$_3$
Authors:
Priya R. Baral,
Oleg I. Utesov,
Samuel H. Moody,
Matthew T. Littlehales,
Pierluigi Gargiani,
Manuel Valvidares,
Robert Cubitt,
Nina-Juliane Steinke,
Chen Luo,
Florin Radu,
Arnaud Magrez,
Jonathan S. White,
Victor Ukleev
Abstract:
The chiral magnetoelectric insulator Cu$_2$OSeO$_3$ hosts a rich and anisotropic magnetic phase diagram that includes helical, conical, field-polarised, tilted conical, and skyrmion lattice phases. Using resonant elastic x-ray scattering (REXS), we uncover a new spiral state confined to the surface of Cu$_2$OSeO$_3$. This surface-confined spiral state (SSS) displays a real-space pitch of $\sim$120…
▽ More
The chiral magnetoelectric insulator Cu$_2$OSeO$_3$ hosts a rich and anisotropic magnetic phase diagram that includes helical, conical, field-polarised, tilted conical, and skyrmion lattice phases. Using resonant elastic x-ray scattering (REXS), we uncover a new spiral state confined to the surface of Cu$_2$OSeO$_3$. This surface-confined spiral state (SSS) displays a real-space pitch of $\sim$120 nm, which remarkably is twice the length of the incommensurate structures observed to-date in Cu$_2$OSeO$_3$. The SSS phase emerges at temperatures below 30~K when the magnetic field is applied between $3^\circ$ to $18^\circ$ away from the $\langle\text{110}\rangle$ crystallographic axes. Its surface localisation is demonstrated through a combination of REXS in reflection and transmission geometries, with complementary small-angle neutron scattering measurements suggesting its absence from the bulk. We attribute the stabilisation of the SSS to competing anisotropic interactions at the crystal surface. The discovery of a robust, surface-confined spiral paves the way for engineering energy-efficient, nanoscale spin-texture platforms for next-generation devices.
△ Less
Submitted 30 April, 2026; v1 submitted 13 July, 2025;
originally announced July 2025.
-
Evidence for magnetoelastic coupling and chiral magnetic ground state in quasi-van der Waals tr-Cr$_{1.22}$Te$_{2}$
Authors:
S. M. Hossain,
B. Rai,
P. R. Baral,
O. Zaharko,
N. Kumar,
A. K. Bera,
M. Majumder
Abstract:
Trigonal tr-Cr$_{1+δ}$Te$_{2}$ is a well-known ferromagnetic material that has recently drawn much attention due to the discovery of zero-field skyrmion state, unusual anomalous Hall effect, topological Hall effect, and topological Nernst effect. This quasi-van der Waals (vdW) layered material with intercalated Cr atoms possesses many peculiar features that depend on the amount of Cr intercalation…
▽ More
Trigonal tr-Cr$_{1+δ}$Te$_{2}$ is a well-known ferromagnetic material that has recently drawn much attention due to the discovery of zero-field skyrmion state, unusual anomalous Hall effect, topological Hall effect, and topological Nernst effect. This quasi-van der Waals (vdW) layered material with intercalated Cr atoms possesses many peculiar features that depend on the amount of Cr intercalation, although the microscopic magnetic ground state is still elusive. We reveal the structural and magnetic properties of tr-Cr$_{1.22}$Te$_{2}$ by low-temperature x-ray diffraction, magnetization, temperature-dependent Raman spectroscopy, and single-crystal neutron diffraction studies. Magnetization measurements under small applied magnetic field indicate two successive magnetic transitions, one from a ferromagnetic (FM) state to an antiferromagnetic (AFM) state (T$_\mathrm{C}=197$ K), and second from AFM to a paramagnetic state (T$_\mathrm{N}=211$ K). The FM transition is sharp with a strong presence of magnetoelastic coupling, but is not accompanied by any structural phase transition. The magnetic structure obtained from zero-field single crystal neutron diffraction reveals that the Cr1 and Cr2 moments are ferromagnetically aligned along the c-axis, while the Cr3 and intercalated Cr4 atoms induce an AFM component in the ab-plane leading to an umbrella-like spin structure which possesses a finite spin chirality. The presence of a finite spin chirality is responsible for the observation of the topological Hall effect (THE).
△ Less
Submitted 12 July, 2025;
originally announced July 2025.
-
Helical spin dynamics in Cu$_2$OSeO$_3$ as measured with small-angle neutron scattering
Authors:
Victor Ukleev,
Priya R. Baral,
Robert Cubitt,
Nina-Juliane Steinke,
Arnaud Magrez,
Oleg I. Utesov
Abstract:
The insulating chiral magnet Cu$_2$OSeO$_3$ exhibits a rich array of low-temperature magnetic phenomena, making it a prime candidate for the study of its spin dynamics. Using spin wave small-angle neutron scattering (SWSANS), we systematically investigated the temperature-dependent behavior of the helimagnon excitations in the field-polarized phase of Cu$_2$OSeO$_3$. Our measurements, spanning 5-5…
▽ More
The insulating chiral magnet Cu$_2$OSeO$_3$ exhibits a rich array of low-temperature magnetic phenomena, making it a prime candidate for the study of its spin dynamics. Using spin wave small-angle neutron scattering (SWSANS), we systematically investigated the temperature-dependent behavior of the helimagnon excitations in the field-polarized phase of Cu$_2$OSeO$_3$. Our measurements, spanning 5-55 K, reveal the temperature evolution of spin-wave stiffness and damping constant with unprecedented resolution, facilitated by the insulating nature of Cu$_2$OSeO$_3$. These findings align with theoretical predictions and resolve discrepancies observed in previous studies, emphasizing the enhanced sensitivity of the SWSANS method. The results provide deeper insights into the fundamental magnetic properties of Cu$_2$OSeO$_3$, contributing to a broader understanding of chiral magnets.
△ Less
Submitted 1 July, 2025;
originally announced July 2025.
-
Triangular lattice magnet GdGa$_2$ with short-period spin cycloids and possible skyrmion phases
Authors:
Priya R. Baral,
Nguyen Duy Khanh,
Masaki Gen,
Hajime Sagayama,
Hironori Nakao,
Taka-hisa Arima,
Yoshichika Ōnuki,
Yoshinori Tokura,
Max Hirschberger
Abstract:
The two-dimensional triangular lattice (TAL) is a model system of magnetic frustration and competing interactions, where skyrmion spin vortices can be induced by a vertical magnetic field $B$. We target the binary compound GdGa$_2$ with an undistorted TAL of Gd$^{3+}$ Heisenberg moments. At higher temperature ($T > 5$ K, $B = 0$, phase II), we reveal the cycloidal spin textures in GdGa$_2$ via res…
▽ More
The two-dimensional triangular lattice (TAL) is a model system of magnetic frustration and competing interactions, where skyrmion spin vortices can be induced by a vertical magnetic field $B$. We target the binary compound GdGa$_2$ with an undistorted TAL of Gd$^{3+}$ Heisenberg moments. At higher temperature ($T > 5$ K, $B = 0$, phase II), we reveal the cycloidal spin textures in GdGa$_2$ via resonant elastic X-ray scattering (REXS). Further, a transition with strong magneto-elastic response occurs when cooling into the zero-field ground state ($T < 5$ K, phase I). We also report the thermodynamic phase boundaries of $B$-induced magnetic A-phases, which are suppressed by an in-plane magnetic field and which have enhanced resistivity due to the partial opening of a charge gap. In analogy to Gd$_2$PdSi$_3$ and GdRu$_2$Si$_2$, these phases may represent a superposition of various cycloids, possibly a Néel skyrmion lattice. Our work lays the basis for further studies of the magnetic phase diagram of GdGa$_2$.
△ Less
Submitted 24 March, 2025;
originally announced March 2025.
-
Fluctuation-driven topological Hall effect in room-temperature itinerant helimagnet Fe3Ga4
Authors:
Priya R. Baral,
Victor Ukleev,
Ivica Živković,
Youngro Lee,
Fabio Orlandi,
Pascal Manuel,
Yurii Skourski,
Lukas Keller,
Anne Stunault,
J. Alberto Rodríguez-Velamazán,
Robert Cubitt,
Arnaud Magrez,
Jonathan S. White,
Igor I. Mazin,
Oksana Zaharko
Abstract:
The topological Hall effect (THE) is a hallmark of a non-trivial geometric spin arrangement in a magnetic metal, originating from a finite scalar spin chirality (SSC). The associated Berry phase is often a consequence of non-coplanar magnetic structures identified by multiple k-vectors. For single-k magnetic structures however with zero SSC, the emergence of a finite topological Hall signal presen…
▽ More
The topological Hall effect (THE) is a hallmark of a non-trivial geometric spin arrangement in a magnetic metal, originating from a finite scalar spin chirality (SSC). The associated Berry phase is often a consequence of non-coplanar magnetic structures identified by multiple k-vectors. For single-k magnetic structures however with zero SSC, the emergence of a finite topological Hall signal presents a conceptual challenge. Here, we report that a fluctuation-driven mechanism involving chiral magnons is responsible for the observed THE in a low-symmetry compound, monoclinic Fe3Ga4. Through neutron scattering experiments, we discovered several nontrivial magnetic phases in this system. In our focus is the helical spiral phase at room temperature, which transforms into a transverse conical state in applied magnetic field, supporting a significant THE signal up to and above room temperature. Our work offers a fresh perspective in the search for novel materials with intertwined topological magnetic and transport properties.
△ Less
Submitted 18 February, 2025;
originally announced February 2025.
-
Metallic $p$-wave magnet with commensurate spin helix
Authors:
Rinsuke Yamada,
Max T. Birch,
Priya R. Baral,
Shun Okumura,
Ryota Nakano,
Shang Gao,
Motohiko Ezawa,
Takuya Nomoto,
Jan Masell,
Yuki Ishihara,
Kamil K. Kolincio,
Ilya Belopolski,
Hajime Sagayama,
Hironori Nakao,
Kazuki Ohishi,
Takashi Ohhara,
Ryoji Kiyanagi,
Taro Nakajima,
Yoshinori Tokura,
Taka-hisa Arima,
Yukitoshi Motome,
Moritz M. Hirschmann,
Max Hirschberger
Abstract:
Antiferromagnetic states with spin-split electronic structure give rise to novel spintronic, magnonic, and electronic phenomena despite (near-) zero net magnetization. The simplest odd-parity spin splitting - $p$-wave - was originally proposed to emerge from a collective instability in interacting electron systems. Recent theory identifies a distinct route to realise $p$-wave spin-split electronic…
▽ More
Antiferromagnetic states with spin-split electronic structure give rise to novel spintronic, magnonic, and electronic phenomena despite (near-) zero net magnetization. The simplest odd-parity spin splitting - $p$-wave - was originally proposed to emerge from a collective instability in interacting electron systems. Recent theory identifies a distinct route to realise $p$-wave spin-split electronic bands without strong correlations, termed $p$-wave magnetism. Here we demonstrate an experimental realisation of a metallic $p$-wave magnet. The odd-parity spin splitting of delocalised conduction electrons arises from their coupling to an antiferromagnetic texture of localised magnetic moments: a coplanar spin helix whose magnetic period is an even multiple of the chemical unit cell, as revealed by X-ray scattering experiments. This texture breaks space inversion symmetry but preserves time-reversal ($T$) symmetry up to a half-unit-cell translation - thereby fulfilling the symmetry conditions for $p$-wave magnetism. Consistent with theoretical predictions, our $p$-wave magnet exhibits a characteristic anisotropy in the electronic conductivity. Relativistic spin-orbit coupling and a tiny spontaneous net magnetization further break $T$ symmetry, resulting in a giant anomalous Hall effect (AHE, $σ_{xy}>600\,$S/cm, Hall angle $>3\,\%$), for an antiferromagnet. Our model calculations show that the spin nodal planes found in the electronic structure of $p$-wave magnets are readily gapped by a small perturbation to induce the AHE.
△ Less
Submitted 9 September, 2025; v1 submitted 14 February, 2025;
originally announced February 2025.
-
Imaging magnetic spiral phases, skyrmion clusters, and skyrmion displacements at the surface of bulk Cu$_2$OSeO$_3$
Authors:
E. Marchiori,
G. Romagnoli,
L. Schneider,
B. Gross,
P. Sahafi,
A. Jordan,
R. Budakian,
P. R. Baral,
A. Magrez,
J. S. White,
M. Poggio
Abstract:
Surfaces -- by breaking bulk symmetries, introducing roughness, or hosting defects -- can significantly influence magnetic order in magnetic materials. Determining their effect on the complex nanometer-scale phases present in certain non-centrosymmetric magnets is an outstanding problem requiring high-resolution magnetic microscopy. Here, we use scanning SQUID-on-tip microscopy to image the surfac…
▽ More
Surfaces -- by breaking bulk symmetries, introducing roughness, or hosting defects -- can significantly influence magnetic order in magnetic materials. Determining their effect on the complex nanometer-scale phases present in certain non-centrosymmetric magnets is an outstanding problem requiring high-resolution magnetic microscopy. Here, we use scanning SQUID-on-tip microscopy to image the surface of bulk Cu$_2$OSeO$_3$ at low temperature and in a magnetic field applied along $\left\langle100\right\rangle$. Real-space maps measured as a function of applied field reveal the microscopic structure of the magnetic phases and their transitions. In low applied field, we observe a magnetic texture consistent with an in-plane stripe phase, pointing to the existence of a distinct surface state. In the low-temperature skyrmion phase, the surface is populated by clusters of disordered skyrmions, which emerge from rupturing domains of the tilted spiral phase. Furthermore, we displace individual skyrmions from their pinning sites by applying an electric potential to the scanning probe, thereby demonstrating local skyrmion control at the surface of a magnetoelectric insulator.
△ Less
Submitted 6 July, 2024;
originally announced July 2024.
-
Short-wave magnons with multipole spin precession detected in the topological bands of a skyrmion lattice
Authors:
Ping Che,
Riccardo Ciola,
Markus Garst,
Volodymyr Kravchuk,
Priya R. Baral,
Arnaud Magrez,
Helmuth Berger,
Thomas Schönenberger,
Henrik M. Rønnow,
Dirk Grundler
Abstract:
Topological magnon bands enable uni-directional edge transport without backscattering, enhancing the robustness of magnonic circuits and providing a novel platform for exploring quantum transport phenomena. Magnetic skyrmion lattices, in particular, host a manifold of topological magnon bands with multipole character and non-reciprocal dispersions. These modes have been explored already in the sho…
▽ More
Topological magnon bands enable uni-directional edge transport without backscattering, enhancing the robustness of magnonic circuits and providing a novel platform for exploring quantum transport phenomena. Magnetic skyrmion lattices, in particular, host a manifold of topological magnon bands with multipole character and non-reciprocal dispersions. These modes have been explored already in the short and long wavelength limit, but previously employed techniques were unable to access intermediate wavelengths comparable to inter-skyrmion distances. Here, we report the detection of such magnons with wavevectors $|{\bf q}|\simeq 48$ rad $μ$m$^{-1}$ in the metastable skyrmion lattice phase of the bulk chiral magnet Cu$_2$OSeO$_3$ using Brillouin light scattering microscopy. Thanks to its high sensitivity and broad bandwidth various multipole excitation modes could be resolved over a wide magnetic field regime. Besides the known counterclockwise, breathing and clockwise modes with dipole character, quantitative comparison of frequencies and spectral weights to theoretical predictions enabled the additional identification of a quadrupole mode and, possibly, a sextupole mode. Our work highlights the potential of skyrmionic phases for the design of magnonic devices exploiting topological magnon states at GHz frequencies.
△ Less
Submitted 9 July, 2025; v1 submitted 22 April, 2024;
originally announced April 2024.
-
Intermediate field-induced phase of the honeycomb magnet BaCo$_2$(AsO$_4$)$_2$
Authors:
Prashanta K. Mukharjee,
Bin Shen,
Sebastian Erdmann,
Anton Jesche,
Julian Kaiser,
Priya R. Baral,
Oksana Zaharko,
Philipp Gegenwart,
Alexander A. Tsirlin
Abstract:
We use magnetometry, calorimetry, and high-resolution capacitive dilatometry, as well as single-crystal neutron diffraction to explore temperature-field phase diagram of the anisotropic honeycomb magnet BaCo$_2$(AsO$_4)_2$. Our data reveal four distinct ordered states observed for in-plane magnetic fields. Of particular interest is the narrow region between 0.51 and 0.55 T that separates the up-up…
▽ More
We use magnetometry, calorimetry, and high-resolution capacitive dilatometry, as well as single-crystal neutron diffraction to explore temperature-field phase diagram of the anisotropic honeycomb magnet BaCo$_2$(AsO$_4)_2$. Our data reveal four distinct ordered states observed for in-plane magnetic fields. Of particular interest is the narrow region between 0.51 and 0.55 T that separates the up-up-down order from the fully polarized state and coincides with the field range where signatures of the spin-liquid behavior have been reported. We show that magnetic Bragg peaks persist in this intermediate phase, thus ruling out its spin-liquid nature. However, the simultaneous nonmonotonic evolution of nuclear Bragg peaks suggests the involvement of the lattice, witnessed also in other regions of the phase diagram where large changes in the sample length are observed upon entering the magnetically ordered states. Our data highlight the importance of lattice effects in BaCo$_2$(AsO$_4)_2$.
△ Less
Submitted 21 October, 2024; v1 submitted 7 March, 2024;
originally announced March 2024.
-
Direct observation of the exchange anisotropy in the helimagnetic insulator Cu$_2$OSeO$_3$
Authors:
Priya R. Baral,
Oleg I. Utesov,
Chen Luo,
Florin Radu,
Arnaud Magrez,
Jonathan S. White,
Victor Ukleev
Abstract:
The helical magnetic structures of cubic chiral systems are well-explained by the competition among Heisenberg exchange, Dzyaloshinskii-Moriya interaction, cubic anisotropy, and anisotropic exchange interaction (AEI). Recently, the role of the latter has been argued theoretically to be crucial for the low-temperature phase diagram of the cubic chiral magnet Cu$_2$OSeO$_3$, which features tilted co…
▽ More
The helical magnetic structures of cubic chiral systems are well-explained by the competition among Heisenberg exchange, Dzyaloshinskii-Moriya interaction, cubic anisotropy, and anisotropic exchange interaction (AEI). Recently, the role of the latter has been argued theoretically to be crucial for the low-temperature phase diagram of the cubic chiral magnet Cu$_2$OSeO$_3$, which features tilted conical and disordered skyrmion states for a specific orientation of the applied magnetic field ($μ_0 \vec{\mathrm{H}} \parallel [001]$). In this study, we exploit transmission resonant x-ray scattering ($t-$REXS) in vector magnetic fields to directly quantify the strength of the AEI in Cu$_2$OSeO$_3$, and measure its temperature dependence. We find that the AEI continuously increases below 50\,K, resulting in a conical spiral pitch variation of $10\%$ in the (001) plane. Our results contribute to establishing the interaction space that supports tilted cone and low-temperature skyrmion state formation, facilitating the goals for both a quantitative description and eventual design of the diverse spiral states existing amongst chiral magnets.
△ Less
Submitted 6 June, 2023;
originally announced June 2023.
-
Tuning topological spin textures in size-tailored chiral magnet insulator particles
Authors:
Priya R. Baral,
Victor Ukleev,
Thomas LaGrange,
Robert Cubitt,
Ivica Zivkovic,
Henrik M. Ronnow,
Jonathan S. White,
Arnaud Magrez
Abstract:
Topological spin textures such as skyrmions hold high potential for use as magnetically active elements in diverse near-future applications. While skyrmions in metallic multilayers attract great attention in this context, unleashing the myriad potential of skyrmions for various applications requires the discovery and customization of alternative host system paradigms. Here we developed and applied…
▽ More
Topological spin textures such as skyrmions hold high potential for use as magnetically active elements in diverse near-future applications. While skyrmions in metallic multilayers attract great attention in this context, unleashing the myriad potential of skyrmions for various applications requires the discovery and customization of alternative host system paradigms. Here we developed and applied a chemical method to synthesize octahedral particles of the chiral insulating skyrmion host Cu2OSeO3 with both narrow size distribution, and tailored dimensions approaching the nanoscale. Combining magnetometry and neutron scattering experiments with micromagnetic simulations, we show that the bulk phase diagram of Cu2OSeO3 changes dramatically below octahedral heights of 400 nm. Further particle size-dependent regimes are identified where various topological spin textures such as skyrmions, merons and bobbers can stabilize, prior to a lower critical octahedral height of approx. 190 nm below which no topological spin texture is found stable. These findings suggest conditions under which sparse topological spin textures confined to chiral magnet nanoparticles can be stable, and provide fresh potential for insulator-based application paradigms.
△ Less
Submitted 21 June, 2022;
originally announced June 2022.
-
Imaging the ultrafast coherent control of a skyrmion crystal
Authors:
Phoebe Tengdin,
Benoit Truc,
Alexey Sapozhnik,
Lingyao Kong,
Nina del Ser,
Simone Gargiulo,
Ivan Madan,
Thomas Schoenenberger,
Priya R. Baral,
Ping Che,
Arnaud Magrez,
Dirk Grundler,
Henrik M. Rønnow,
Thomas Lagrange,
Jiadong Zang,
Achim Rosch,
Fabrizio Carbone
Abstract:
Exotic magnetic textures emerging from the subtle interplay between thermodynamic and topological fluctuation have attracted intense interest due to their potential applications in spintronic devices. Recent advances in electron microscopy have enabled the imaging of random photo-generated individual skyrmions. However, their deterministic and dynamical manipulation is hampered by the chaotic natu…
▽ More
Exotic magnetic textures emerging from the subtle interplay between thermodynamic and topological fluctuation have attracted intense interest due to their potential applications in spintronic devices. Recent advances in electron microscopy have enabled the imaging of random photo-generated individual skyrmions. However, their deterministic and dynamical manipulation is hampered by the chaotic nature of such fluctuations and the intrinsically irreversible switching between different minima in the magnetic energy landscape. Here, we demonstrate a method to coherently control the rotation of a skyrmion crystal by discrete amounts at speeds which are much faster than previously observed. By employing circularly polarized femtosecond laser pulses with an energy below the bandgap of the Mott insulator Cu2OSeO3, we excite a collective magnon mode via the inverse Faraday effect. This triggers coherent magnetic oscillations that directly control the rotation of a skyrmion crystal imaged by cryo-Lorentz Transmission Electron Microscopy. The manipulation of topological order via ultrafast laser pulses shown here can be used to engineer fast spin-based logical devices.
△ Less
Submitted 22 July, 2022; v1 submitted 9 October, 2021;
originally announced October 2021.
-
Accuracy and speed of elongation in a minimal model of DNA replication
Authors:
M Sahoo,
Arsha N,
P R Baral,
S Klumpp
Abstract:
Being a dual purpose enzyme, the DNA polymerase is responsible for elongation of the newly formed DNA strand as well as cleaving the erroneous growth in case of a misincorporation. The efficiency of replication depends on the coordination of the polymerization and exonuclease activity of DNA polymerase. Here we propose and analyze a minimal kinetic model of DNA replication and determine exact expr…
▽ More
Being a dual purpose enzyme, the DNA polymerase is responsible for elongation of the newly formed DNA strand as well as cleaving the erroneous growth in case of a misincorporation. The efficiency of replication depends on the coordination of the polymerization and exonuclease activity of DNA polymerase. Here we propose and analyze a minimal kinetic model of DNA replication and determine exact expressions for the velocity of elongation and the accuracy of replication. We first analyze the case without exonuclease activity. In that case, accuracy is determined by a kinetic competition between stepping and unbinding, with discrimination between correct and incorrect nucleotides in both transitions. We then include exonuclease activity and ask how different modes of additional discrimination in the exonuclease pathway can improve the accuracy while limiting the detrimental effect of exonuclase on the speed of replication. In this way, we ask how the kinetic parameters of the model have to be set to coordinate the two activities of the enzyme for high accuracy and high speed. The analysis also shows that the design of a replication system does not universally have to follow the speed-accuracy trade-off rule, although it does in the biologically realized parameter range. The accuracy of the process is mainly controlled by the crucial role of stepping after erroneous incorporation, which has impact on both polymerase and exonuclease activities of DNA polymerase.
△ Less
Submitted 27 September, 2021;
originally announced September 2021.
-
Cluster spin-glass behaviour and memory effect in Cr$_{0.5}$Fe$_{0.5}$Ga
Authors:
Pallab Bag,
P. R. Baral,
R. Nath
Abstract:
We report the structural, static, and dynamic properties of Cr$_{0.5}$Fe$_{0.5}$Ga by means of powder x-ray diffraction, magnetization, heat capacity, magnetic relaxation, and magnetic memory effect measurements. DC magnetization and AC susceptibility studies reveal a spin-glass transition at around $T_{\rm f} \simeq 22$~K. An intermediate value of the relative shift in freezing temperature…
▽ More
We report the structural, static, and dynamic properties of Cr$_{0.5}$Fe$_{0.5}$Ga by means of powder x-ray diffraction, magnetization, heat capacity, magnetic relaxation, and magnetic memory effect measurements. DC magnetization and AC susceptibility studies reveal a spin-glass transition at around $T_{\rm f} \simeq 22$~K. An intermediate value of the relative shift in freezing temperature $δT_{\rm f} \simeq 0.017$, obtained from the AC susceptibility data reflects the formation of cluster spin-glass states. The frequency dependence of $T_{\rm f}$ is also analyzed within the framework of dynamic scaling laws. The analysis using power law yields a time constant for a single spin flip $τ* \simeq 1.1\times10^{-10}$~s and critical exponent $zν^{\prime}=4.2\pm0.2$. On the other hand, the Vogel-Fulcher (VF) law yields the time constant for a single spin flip $τ_0 \simeq 6.6\times10^{-9}$~s, VF temperature $T_{\rm 0}=21.1\pm0.1$~K, and an activation energy $E_{\rm a}/k_{\rm B} \simeq 16$~K. The value of $τ*$ and $τ_0$ along with a non-zero value of $T_{\rm 0}$ provide further evidence for the cluster spin-glass behaviour. The magnetic field dependent $T_{\rm f}$ follows the de Almeida-Thouless line with a non-mean-field type instability, reflecting either a different universality class or strong anisotropy in the spin system. A detailed non-equilibrium dynamics study via relaxation and memory effect experiments demonstrates striking memory effects. All the above observations render a cluster spin-glass behaviour which is triggered by magnetic frustration due to competing antiferromagnetic and ferromagnetic interactions and magnetic site disorder. Moreover, the asymmetric response of magnetic relaxation with respect to the change in temperature, below $T_{\rm f}$ can be explained by the hierarchical model.
△ Less
Submitted 9 October, 2018;
originally announced October 2018.