Showing 1–13 of 13 results for author: Jani, H

Revealing the origin of XMCD in an altermagnet via three-dimensional control of spins

Authors: Daire Mallon, Zixuan Wu, Jheng-Cyuan Lin, Ruiwen Xie, Bo Zhao, Charles Godfrey, Qing He, Lucia Iglesias, Pierluigi Gargiani, Manuel Valvidares, Peter Bencok, Francesco Maccherozzi, Larissa S. I. Veiga, Paul Steadman, Manuel Bibes, Hongbin Zhang, Paolo G. Radaelli, Hariom Jani

Abstract: Altermagnets are an emerging class of collinear antiferromagnets that exhibit unconventional spin-polarised electronic bands, potentially unlocking new functionalities that do not rely on spin-orbit coupling (SOC). Experimental signatures traditionally associated with spin polarisation, like X-ray magnetic circular dichroism (XMCD), are thus being used as a validation of altermagnetism. However, u… ▽ More Altermagnets are an emerging class of collinear antiferromagnets that exhibit unconventional spin-polarised electronic bands, potentially unlocking new functionalities that do not rely on spin-orbit coupling (SOC). Experimental signatures traditionally associated with spin polarisation, like X-ray magnetic circular dichroism (XMCD), are thus being used as a validation of altermagnetism. However, unlike altermagnetic spin-splitting, these responses require SOC and are not invariant under spin-space rotations. This brings into question the extent to which they can be considered direct signatures of altermagnetism. Here, we exploit the g-wave altermagnet $α$-Fe$_{2}$O$_{3}$ to demonstrate that XMCD is governed precisely by the spin-direction-induced symmetry breaking that altermagnetic spin groups are designed to ignore. Strikingly, the XMCD is highly anisotropic and is decoupled from the weak magnetic canting. We show that this anomalous XMCD can be described by on-site Faraday tensors capturing the locally uncompensated spin-orbital anisotropies - a scenario that can be applied to other altermagnets. Leveraging this, we reconstruct complete vectorial maps of nanoscale textures in $α$-Fe$_{2}$O$_{3}$ thin films, including domain walls and topological solitons, which are promising for building future spintronics and magnonics devices. △ Less

Submitted 1 May, 2026; originally announced May 2026.

Comments: 6 Figures

The 2026 Skyrmionics Roadmap

Authors: Sabri Koraltan, Claas Abert, Manfred Albrecht, Maria Azhar, Christian Back, Hélène Béa, Max T. Birch, Stefan Blügel, Olivier Boulle, Felix Büttner, Ping Che, Vincent Cros, Emily Darwin, Louise Desplat, Claire Donnelly, Haifeng Du, Karin Everschor-Sitte, Amalio Fernández-Pacheco, Simone Finizio, Giovanni Finocchio, Markus Garst, Raphael Gruber, Dirk Grundler, Satoru Hayami, Thorsten Hesjedal , et al. (42 additional authors not shown)

Abstract: Magnetic skyrmions and related topological spin textures have emerged as a central topic in condensed-matter physics, combining fundamental significance with potential for transformative applications in spintronics, magnonics, and beyond. Over the past decade, advances in material platforms, imaging techniques, theoretical modeling, and device concepts have established skyrmionics as a rapidly exp… ▽ More Magnetic skyrmions and related topological spin textures have emerged as a central topic in condensed-matter physics, combining fundamental significance with potential for transformative applications in spintronics, magnonics, and beyond. Over the past decade, advances in material platforms, imaging techniques, theoretical modeling, and device concepts have established skyrmionics as a rapidly expanding field. At the same time, challenges remain in stabilizing, controlling, and integrating such textures into functional architectures, while novel phenomena such as antiskyrmions, higher-order skyrmions, hopfions, and antiferromagnetic textures arise. The 2026 Skyrmionics Roadmap represents a collective effort of many authors, providing a comprehensive perspective on the current state-of-the-art and the outlook for the coming years. In 33 focused sections, each co-authored by two researchers, we chart progress in theory and modeling, material systems, skyrmion dynamics, and skyrmion technologies. By offering a consolidated vision, this Roadmap aims to guide both fundamental research and application-driven efforts, accelerating the transition of skyrmionics from conceptual breakthroughs toward practical technologies. △ Less

Submitted 23 January, 2026; originally announced January 2026.

Comments: 244 Pages, 33 Sections, 52 Figures

Room temperature control of axial and basal antiferromagnetic anisotropies using strain

Authors: Jack Harrison, Junxiong Hu, Charles Godfrey, Jheng-Cyuan Lin, Tim A Butcher, Jörg Raabe, Simone Finizio, Hariom Jani, Paolo G Radaelli

Abstract: Antiferromagnetic materials are promising platforms for the development of ultra-fast spintronics and magnonics due to their robust magnetism, high-frequency relativistic dynamics, low-loss transport, and the ability to support topological textures. However, achieving deterministic control over antiferromagnetic order in thin films is a major challenge, due to the formation of multi-domain states… ▽ More Antiferromagnetic materials are promising platforms for the development of ultra-fast spintronics and magnonics due to their robust magnetism, high-frequency relativistic dynamics, low-loss transport, and the ability to support topological textures. However, achieving deterministic control over antiferromagnetic order in thin films is a major challenge, due to the formation of multi-domain states stabilised by competing magnetic and destressing interactions. Thus, the successful implementation of antiferromagnetic materials necessitates careful engineering of their anisotropy. Here, we demonstrate strain-based robust control over multiple antiferromagnetic anisotropies and nanoscale domains in the promising spintronic candidate a-Fe2O3, at room temperature. By applying isotropic and anisotropic in-plane strains across a broad temperature-strain phase space, we systematically tune the interplay between magneto-crystalline and magneto-elastic interactions. We discover that strain-driven control steers the system towards an aligned antiferromagnetic state, whilst preserving topological spin textures, such as merons, antimerons and bimerons. We directly map the nanoscale antiferromagnetic order using linear dichroic scanning transmission X-ray microscopy integrated with in situ strain and temperature control. A Landau model and micromagnetic simulations reveal how strain reshapes the magnetic energy landscape. These findings suggest that strain could serve as a versatile control mechanism to reconfigure equilibrium or dynamic antiferromagnetic states on demand in a-Fe2O3, paving the way for next-generation spintronic and magnonic devices. △ Less

Submitted 14 October, 2025; originally announced October 2025.

Comments: *Correspondence: hariom.jani@physics.ox.ac.uk; †These authors contributed equally

Holographic imaging of antiferromagnetic domains with in-situ magnetic field

Authors: Jack Harrison, Hariom Jani, Junxiong Hu, Manohar Lal, Jheng-Cyuan Lin, Horia Popescu, Jason Brown, Nicolas Jaouen, A. Ariando, Paolo G. Radaelli

Abstract: Lensless coherent x-ray imaging techniques have great potential for high-resolution imaging of magnetic systems with a variety of in-situ perturbations. Despite many investigations of ferromagnets, extending these techniques to the study of other magnetic materials, primarily antiferromagnets, is lacking. Here, we demonstrate the first (to our knowledge) study of an antiferromagnet using holograph… ▽ More Lensless coherent x-ray imaging techniques have great potential for high-resolution imaging of magnetic systems with a variety of in-situ perturbations. Despite many investigations of ferromagnets, extending these techniques to the study of other magnetic materials, primarily antiferromagnets, is lacking. Here, we demonstrate the first (to our knowledge) study of an antiferromagnet using holographic imaging through the "holography with extended reference by autocorrelation linear differential operation" technique. Energy-dependent contrast with both linearly and circularly polarised x-rays are demonstrated. Antiferromagnetic domains and topological textures are studied in the presence of applied magnetic fields, demonstrating quasi-cyclic domain reconfiguration up to 500 mT. △ Less

Submitted 13 October, 2023; originally announced October 2023.

Comments: 14 pages, 6 figures

Revealing Emergent Magnetic Charge in an Antiferromagnet with Diamond Quantum Magnetometry

Authors: Anthony K. C. Tan, Hariom Jani, Michael Högen, Lucio Stefan, Claudio Castelnovo, Daniel Braund, Alexandra Geim, Matthew S. G. Feuer, Helena S. Knowles, Ariando Ariando, Paolo G. Radaelli, Mete Atatüre

Abstract: Whirling topological textures play a key role in exotic phases of magnetic materials and offer promise for logic and memory applications. In antiferromagnets, these textures exhibit enhanced stability and faster dynamics with respect to ferromagnetic counterparts, but they are also difficult to study due to their vanishing net magnetic moment. One technique that meets the demand of highly sensitiv… ▽ More Whirling topological textures play a key role in exotic phases of magnetic materials and offer promise for logic and memory applications. In antiferromagnets, these textures exhibit enhanced stability and faster dynamics with respect to ferromagnetic counterparts, but they are also difficult to study due to their vanishing net magnetic moment. One technique that meets the demand of highly sensitive vectorial magnetic field sensing with negligible backaction is diamond quantum magnetometry. Here, we show that the archetypal antiferromagnet, hematite, hosts a rich tapestry of monopolar, dipolar and quadrupolar emergent magnetic charge distributions. The direct readout of the previously inaccessible vorticity of an antiferromagnetic spin texture provides the crucial connection to its magnetic charge through a duality relation. Our work defines a novel paradigmatic class of magnetic systems to explore two-dimensional monopolar physics, and highlights the transformative role that diamond quantum magnetometry could play in exploring emergent phenomena in quantum materials. △ Less

Submitted 21 March, 2023; originally announced March 2023.

Spatially reconfigurable topological textures in freestanding antiferromagnetic nanomembranes

Authors: Hariom Jani, Jack Harrison, Sonu Hooda, Saurav Prakash, Proloy Nandi, Junxiong Hu, Zhiyang Zeng, Jheng-Cyuan Lin, Ganesh ji Omar, Jörg Raabe, Simone Finizio, Aaron Voon-Yew Thean, A Ariando, Paolo G Radaelli

Abstract: Antiferromagnets hosting real-space topological spin textures are promising platforms to model fundamental ultrafast phenomena and explore spintronics. However, to date, they have only been fabricated epitaxially on specific symmetry-matched crystalline substrates, to preserve their intrinsic magneto-crystalline order. This curtails their integration with dissimilar supports, markedly restricting… ▽ More Antiferromagnets hosting real-space topological spin textures are promising platforms to model fundamental ultrafast phenomena and explore spintronics. However, to date, they have only been fabricated epitaxially on specific symmetry-matched crystalline substrates, to preserve their intrinsic magneto-crystalline order. This curtails their integration with dissimilar supports, markedly restricting the scope of fundamental and applied investigations. Here, we circumvent this limitation by designing detachable crystalline antiferromagnetic nanomembranes of $α$-Fe$_{2}$O$_{3}$, that can be transferred onto other desirable supports after growth. We develop transmission-based antiferromagnetic vector-mapping to show that these nanomembranes harbour rich topological phenomenology at room temperature. Moreover, we exploit their extreme flexibility to demonstrate three-dimensional reconfiguration of antiferromagnetic properties, driven locally via flexure-induced strains. This allows us to spatially design antiferromagnetic states outside their typical thermal stability window. Integration of such freestanding antiferromagnetic layers with flat or curved nanostructures could enable spin texture designs tailored by magnetoelastic-/geometric-effects in the quasi-static and dynamical regimes, opening new explorations into curvilinear antiferromagnetism and unconventional computing. △ Less

Submitted 6 March, 2023; originally announced March 2023.

Comments: 17 pages, 4 figures

Journal ref: Nature Materials 23, 619 (2024)

A route towards stable homochiral topological textures in A-type antiferromagnets

Authors: Jack Harrison, Hariom Jani, Paolo G. Radaelli

Abstract: Topologically protected whirling magnetic textures could emerge as data carriers in next-generation post-Moore computing. Such textures are abundantly observed in ferromagnets (FMs); however, their antiferromagnetic (AFM) counterparts are expected to be even more relevant for device applications, as they promise ultra-fast, deflection-free dynamics whilst being robust against external fields. Unfo… ▽ More Topologically protected whirling magnetic textures could emerge as data carriers in next-generation post-Moore computing. Such textures are abundantly observed in ferromagnets (FMs); however, their antiferromagnetic (AFM) counterparts are expected to be even more relevant for device applications, as they promise ultra-fast, deflection-free dynamics whilst being robust against external fields. Unfortunately, they have remained elusive, hence identifying materials hosting such textures is key to developing this technology. Here, we present comprehensive micromagnetic and analytical models investigating topological textures in the broad material class of A-type antiferromagnets, specifically focusing on the prototypical case of $α\text{-Fe}_2 \text{O}_3$,an emerging candidate for AFM spintronics. By exploiting a symmetry breaking interfacial Dzyaloshinskii-Moriya interaction (iDMI), it is possible to stabilize a wide topological family, including AFM (anti)merons and bimerons and the hitherto undiscovered AFM skyrmions. Whilst iDMI enforces homochirality and improves the stability of these textures, the widely tunable anisotropy and exchange interactions enable unprecedented control of their core dimensions. We then present a unifying framework to model the scaling of texture sizes based on a simple dimensional analysis. As the parameters required to host and tune homochiral AFM textures may be obtained by rational materials design of $α\text{-Fe}_2 \text{O}_3$, it could emerge as a promising platform to initiate AFM topological spintronics. △ Less

Submitted 30 November, 2021; originally announced November 2021.

Comments: 17 pages, 9 figures. Submitted to Physical Review X

Skyrmionics in correlated oxides

Authors: Zhi Shiuh Lim, Hariom Jani, T. Venkatesan, A. Ariando

Abstract: While chiral magnets, metal-based magnetic multilayers, or Heusler compounds have been considered as the material workhorses in the field of skyrmionics, oxides are now emerging as promising alternatives, as they host special correlations between the spin-orbital-charge-lattice degrees of freedom and/or coupled ferroic order parameters. These interactions open new possibilities for practically exp… ▽ More While chiral magnets, metal-based magnetic multilayers, or Heusler compounds have been considered as the material workhorses in the field of skyrmionics, oxides are now emerging as promising alternatives, as they host special correlations between the spin-orbital-charge-lattice degrees of freedom and/or coupled ferroic order parameters. These interactions open new possibilities for practically exploiting skyrmionics. In this article, we review the recent advances in the observation and control of topological spin textures in various oxide systems. We start with the discovery of skyrmions and related quasiparticles in bulk and heterostructure ferromagnetic oxides. Next, we emphasize the shortcomings of implementing ferromagnetic textures, which have led to the recent explorations of ferrimagnetic and antiferromagnetic oxide counterparts, with higher Curie temperatures, stray-field immunity, low Gilbert damping, ultrafast magnetic dynamics, and/or absence of skyrmion deflection. Then, we highlight the development of novel pathways to control the stability, motion, and detection of topological textures using electric fields and currents. Finally, we present the outstanding challenges that need to be overcome to achieve all-electrical, nonvolatile, low-power oxide skyrmionic devices. △ Less

Submitted 13 February, 2022; v1 submitted 20 November, 2021; originally announced November 2021.

Comments: Authors Zhi Shiuh Lim and Hariom Jani have contributed equally; 22 Pages, 4 Figures; Keywords: Spintronics, Topology, Oxides, Ferrimagnets, Antiferromagnets, Skyrmions, Beyond-Moore Computing

Journal ref: MRS Bulletin 46, 1053 (2021)

Experimental Evidence of t2g Electron-Gas Rashba Interaction Induced by Asymmetric Orbital Hybridization

Authors: Ganesh Ji Omar, Weilong Kong, Hariom Jani, Mengsha Li, Jun Zhou, Zhi Shiuh Lim, Saurav Prakash, Shengwei Zeng, Sonu Hooda, Thirumalai Venkatesan, Yuan Ping Feng, Stephen J. Pennycook, Shen Lei, A. Ariando

Abstract: We report the control of Rashba spin-orbit interaction by tuning asymmetric hybridization between Ti-orbitals at the LaAlO3/SrTiO3 interface. This asymmetric orbital hybridization is modulated by introducing a LaFeO3 layer between LaAlO3 and SrTiO3, which alters the Ti-O lattice polarization and traps interfacial charge carriers, resulting in a large Rashba spin-orbit effect at the interface in th… ▽ More We report the control of Rashba spin-orbit interaction by tuning asymmetric hybridization between Ti-orbitals at the LaAlO3/SrTiO3 interface. This asymmetric orbital hybridization is modulated by introducing a LaFeO3 layer between LaAlO3 and SrTiO3, which alters the Ti-O lattice polarization and traps interfacial charge carriers, resulting in a large Rashba spin-orbit effect at the interface in the absence of an external bias. This observation is verified through high-resolution electron microscopy, magneto-transport and first-principles calculations. Our results open hitherto unexplored avenues of controlling Rashba interaction to design next-generation spin-orbitronics. △ Less

Submitted 5 November, 2022; v1 submitted 13 October, 2021; originally announced October 2021.

Comments: Total 30 Pages and 18 figures in the main article including supplementary information

Journal ref: Phys. Rev. Lett. 129, 187203 (2022)

Photoelectron Transportation Dynamics in GaAs Photocathodes

Authors: Rui Zhou, Hemang Jani, Yijun Zhang, Yunsheng Qian, Lingze Duan

Abstract: We report here a general theory describing photoelectron transportation dynamics in GaAs semiconductor photocathodes. Gradient doping is incorporated in the model through the inclusion of directional carrier drift. The time-evolution of electron concentration in the active layer upon the injection of an excitation pulse is solved both numerically and analytically. The predictions of the model are… ▽ More We report here a general theory describing photoelectron transportation dynamics in GaAs semiconductor photocathodes. Gradient doping is incorporated in the model through the inclusion of directional carrier drift. The time-evolution of electron concentration in the active layer upon the injection of an excitation pulse is solved both numerically and analytically. The predictions of the model are compared with experiments via carrier-induced transient reflectivity change, which is measured for gradient-doped and uniform-doped photocathodes using femtosecond pump-probe reflectometry. Excellent agreement is found between the experiments and the theory, leading to the characterization of key device parameters such as diffusion constant and electron decay rates. Comparisons are also made between uniform doping and gradient doping for their characteristics in photoelectron transportation. Doping gradient is found to be able to accelerate electron accumulation on the device surface. These results offer new insights into the dynamics of III-V photocathodes and potentially open a new avenue toward experimental characterization of device parameters. △ Less

Submitted 30 August, 2021; originally announced September 2021.

Antiferromagnetic Half-skyrmions and Bimerons at room temperature

Authors: Hariom Jani, Jheng-Cyuan Lin, Jiahao Chen, Jack Harrison, Francesco Maccherozzi, Jonathon Schad, Saurav Prakash, Chang-Beom Eom, A. Ariando, T. Venkatesan, Paolo G. Radaelli

Abstract: In the quest for post-CMOS technologies, ferromagnetic skyrmions and their anti-particles have shown great promise as topologically protected solitonic information carriers in memory-in-logic or neuromorphic devices. However, the presence of dipolar fields in ferromagnets, restricting the formation of ultra-small topological textures, and the deleterious skyrmion Hall effect when driven by spin to… ▽ More In the quest for post-CMOS technologies, ferromagnetic skyrmions and their anti-particles have shown great promise as topologically protected solitonic information carriers in memory-in-logic or neuromorphic devices. However, the presence of dipolar fields in ferromagnets, restricting the formation of ultra-small topological textures, and the deleterious skyrmion Hall effect when driven by spin torques have thus far inhibited their practical implementations. Antiferromagnetic analogues, which are predicted to demonstrate relativistic dynamics, fast deflection-free motion and size scaling have recently come into intense focus, but their experimental realizations in natural antiferromagnetic systems are yet to emerge. Here, we demonstrate a family of topological antiferromagnetic spin-textures in $α$-Fe$_2$O$_3$ - an earth-abundant oxide insulator - capped with a Pt over-layer. By exploiting a first-order analogue of the Kibble-Zurek mechanism, we stabilize exotic merons-antimerons (half-skyrmions), and bimerons, which can be erased by magnetic fields and re-generated by temperature cycling. These structures have characteristic sizes of the order ~100 nm that can be chemically controlled via precise tuning of the exchange and anisotropy, with pathways to further scaling. Driven by current-based spin torques from the heavy-metal over-layer, some of these AFM textures could emerge as prime candidates for low-energy antiferromagnetic spintronics at room temperature. △ Less

Submitted 18 November, 2020; v1 submitted 22 June, 2020; originally announced June 2020.

Comments: 18 pages, 4 figures

Journal ref: Nature 590, 74 (2021)

Phase diagram and superconducting dome of infinite-layer $\mathrm{Nd_{1-x}Sr_{x}NiO_{2}}$ thin films

Authors: Shengwei Zeng, Chi Sin Tang, Xinmao Yin, Changjian Li, Mengsha Li, Zhen Huang, Junxiong Hu, Wei Liu, Ganesh Ji Omar, Hariom Jani, Zhi Shiuh Lim, Kun Han, Dongyang Wan, Ping Yang, Stephen John Pennycook, Andrew T. S. Wee, Ariando Ariando

Abstract: Infinite-layer Nd1-xSrxNiO2 thin films with Sr doping level x from 0.08 to 0.3 were synthesized and investigated. We found a superconducting dome to be between 0.12 and 0.235 which is accompanied by a weakly insulating behaviour in both underdoped and overdoped regimes. The dome is akin to that in the electron-doped 214-type and infinite-layer cuprate superconductors. For x higher than 0.18, the n… ▽ More Infinite-layer Nd1-xSrxNiO2 thin films with Sr doping level x from 0.08 to 0.3 were synthesized and investigated. We found a superconducting dome to be between 0.12 and 0.235 which is accompanied by a weakly insulating behaviour in both underdoped and overdoped regimes. The dome is akin to that in the electron-doped 214-type and infinite-layer cuprate superconductors. For x higher than 0.18, the normal state Hall coefficient ($R_{H}$) changes the sign from negative to positive as the temperature decreases. The temperature of the sign changes monotonically decreases with decreasing x from the overdoped side and approaches the superconducting dome at the mid-point, suggesting a reconstruction of the Fermi surface as the dopant concentration changes across the center of the dome. △ Less

Submitted 2 October, 2020; v1 submitted 23 April, 2020; originally announced April 2020.

Comments: 23 pages (including Supplemental Material), 12 Figures (including 8 supplemental figures)

Journal ref: Phys. Rev. Lett. 125, 147003 (2020)

Tunable and Enhanced Rashba Spin-Orbit Coupling in Iridate-Manganite Heterostructures

Authors: T. S. Suraj, Ganesh Ji Omar, Hariom Jani, Muhammad Mangattuchali Juvaid, Sonu Hooda, Anindita Chaudhuri, Andrivo Rusydi, Kanikrishnan Sethupathi, Thirumalai Venkatesan, Ariando Ariando, Mamidanna Sri Ramachandra Rao

Abstract: Tailoring spin-orbit interactions and Coulomb repulsion are the key features to observe exotic physical phenomena such as magnetic anisotropy and topological spin texture at oxide interfaces. Our study proposes a novel platform for engineering the magnetism and spin-orbit coupling at LaMnO3/SrIrO3 (3d-5d oxide) interfaces by tuning the LaMnO3 growth conditions which controls the lattice displaceme… ▽ More Tailoring spin-orbit interactions and Coulomb repulsion are the key features to observe exotic physical phenomena such as magnetic anisotropy and topological spin texture at oxide interfaces. Our study proposes a novel platform for engineering the magnetism and spin-orbit coupling at LaMnO3/SrIrO3 (3d-5d oxide) interfaces by tuning the LaMnO3 growth conditions which controls the lattice displacement and spin-correlated interfacial coupling through charge transfer. We report on a tunable and enhanced interface-induced Rashba spin-orbit coupling and Elliot-Yafet spin relaxation mechanism in LaMnO3/SrIrO3 bilayer with change in the underlying magnetic order of LaMnO3. We also observed enhanced spin-orbit coupling strength in LaMnO3/SrIrO3 compared to previously reported SrIrO3 layers. The X-Ray spectroscopy measurement reveals the quantitative valence of Mn and their impact on charge transfer. Further, we performed angle-dependent magnetoresistance measurements, which show signatures of magnetic proximity effect in SrIrO3 while reflecting the magnetic order of LaMnO3. Our work thus demonstrates a new route to engineer the interface induced Rashba spin-orbit coupling and magnetic proximity effect in 3d-5d oxide interfaces which makes SrIrO3 an ideal candidate for spintronics applications. △ Less

Submitted 1 April, 2020; originally announced April 2020.

Comments: 10 Pages, 4 Figures

Journal ref: Phys. Rev. B 102, 125145 (2020)