Research

A joint publication with Jairo Sinova and Ricardo Zarzuela about spin-transfer and topological Hall effects in itinerant frustrated magnets has been published in Physical Review B.

They examine the spin-transfer and topological Hall physics of metallic frustrated magnets and show that SO(3) solitons and magnetic disclinations mediate previously unidentified contributions to the corresponding effects, with no analog in collinear magnetism. In particular, they present a minimal low-energy long-wavelength theory of the Yang-Mills type for the itinerant carriers and also discuss the emergent electrodynamics mediated by the topological solitons/defects arising in the noncoplanar magnetic background. They also considered the effect of symmetry reduction (with respect to the case of full rotational symmetry) on both spin-transfer and topological Hall responses of the magnetic conductor. Furthermore, they discuss experimental setups for the detection of the aforesaid Hall currents. Their findings open new avenues for the detection of topological solitons/defects in magnetic systems with order-parameter manifolds beyond the conventional S2 paradigm.

A joint publication with Jairo Sinova and Libor Šmejkal about the saturation of the anomalous Hall effect at high magnetic fields in altermagnetic RuO2 has been published in APL Materials.

They used a field-induced reorientation of the Néel vector from the easy-axis toward the [110] hard-axis to demonstrate the anomalous Hall signal in this RuO2. They confirm the existence of an anomalous Hall effect in our RuO2 thin-film samples, whose set of magnetic and magneto-transport characteristics is consistent with the earlier report. By performing their measurements at extreme magnetic fields up to 68 T, they reach saturation of the anomalous Hall signal at a field Hc ≃ 55 T that was inaccessible in earlier studies but is consistent with the expected Néel-vector reorientation field.

A publication with Helen Gomonay about nonlinear magnon dynamics in Mn2Au has been published in Nature Communications.

They excite Mn2Au thin films with phase-locked single-cycle terahertz electromagnetic pulses and monitor the spin response with femtosecond magneto-optic probes. They observe signals whose symmetry, dynamics, terahertz-field scaling and dependence on sample structure are fully consistent with a uniform in-plane antiferromagnetic magnon driven by field-like terahertz NSOTs with a torkance of (150 ± 50) cm2 A−1 s−1. Their research indicates that fully coherent Néel-vector switching by 90° within 1 ps is within close reach.

A joint publication with Tobias Wagner and Helen Gomonay about coupling of ferromagnetic and antiferromagnetic spin dynamics in Mn2Au/NiFe thin film bilayers has been published in Physical Review Letters.

They investigate magnetization dynamics of ${\mathrm{Mn}}_2\mathrm{Au}/\mathrm{Py}$ (${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$) thin film bilayers using broadband ferromagnetic resonance (FMR) and Brillouin light scattering spectroscopy. Their model reveals the dependence of the hybrid modes on the AFMR frequencies and interfacial coupling as well as the evanescent character of the spin waves that extend across the ${\mathrm{Mn}}_2\mathrm{Au}/\mathrm{Py}$ interface.

A joint publication with Olena Gomonay about photocurrents, the Inverse faraday effect, and photospin Hall effect in Mn2Au has been published in APL Materials.

They reveal the emergence of large photocurrents of spin in collinear Mn₂Au, whose properties can be understood as a result of a non-linear optical version of the spin Hall effect, which they refer to as the photospin Hall effect, encoded into the relation between the driving charge and resulting spin photocurrents. Moreover, they suggest that even a very small canting in Mn₂Au can give rise to colossal spin photocurrents that are chiral in flavor. They conclude that the combination of staggered magnetization with the structural and electronic properties of this material results in a unique blend of prominent
photocurrents, which makes Mn₂Au a unique platform for advanced optospintronics applications.

You can find the publication under APL Mater 11, 071106.

A joint publication with Libor Šmejkal about the electronic structure of the electrically switchable antiferromagnet CuMnAs has been published in npj Quantum Materials.

They report direct measurements of the electronic structure of single-crystalline thin films of tetragonal CuMnAs using angle-resolved photoemission spectroscopy (ARPES), including Fermi surfaces (FS) and energy-wavevector dispersions. This work underscores the need to control the chemical potential in tetragonal CuMnAs to enable the exploration and exploitation of the Dirac fermions with tunable masses, which are predicted to be above the chemical potential in the present samples.

You can find the publication under npj Quantum Materials volume 8, Article number: 19 (2023).

A joint publication with Jairo Sinova and Helen Gomonay about magnon eigenmode and polarization control in the easy-plane phase of hematite has been published in Physical Review B.

They describe how magnon eigenmodes in easy-plane antiferromagnetic insulators are linearly polarized and are not expected to carry any net spin angular momentum. Motivated by recent nonlocal spin transport experiments in the easy-plane phase of hematite, they perform a series of micromagnetic simulations in a nonlocal geometry at finite temperatures. They show that by tuning an external magnetic field, they can control the magnon eigenmodes and the polarization of the spin transport signal in these systems. They argue that a coherent beating oscillation between two orthogonal linearly polarized magnon eigenmodes is the mechanism responsible for finite spin transport in easy-plane antiferromagnetic insulators. The sign of the detected spin signal is also naturally explained by the proposed coherent beating mechanism. Their finding opens a path for on-demand control of the spin signal in a large class of easy-plane antiferromagnetic insulators.

You can find the publication under Phys. Rev. B 107, 184404 (2023).

A joint publication with Jairo Sinova  and Helen Gomonay about magnon generation in NiO/Pt films has been published in Nature communications.

They demonstrate the combined generation of broadband and narrowband magnons in thin films of NiO/Pt. They present two excitation processes which both lead to the emmision of THz signals. These results open new routes towards the development of fast opto-spintronic devices based on antiferromagnetic materials.

You can find the publication under nature.com/articles/s41467-023-37509-6.

A joint publication with Helen Gomonay about spintronics in insulating 3d metal oxides with antiferromagnetic coupling has been published in Applied Physics Letters.

They describe that antiferromagnetic transition metal oxides are an established and widely studied materials system in the context of spin-based electronics, commonly used as passive elements in exchange bias-based memory devices. Currently, major interest has resurged due to the recent observation of long-distance spin transport, current-induced switching, and THz emission. As a result, insulating transition metal oxides are now considered to be attractive candidates for active elements in future spintronic devices. They discuss some of the most promising materials systems and highlight recent advances in reading and writing antiferromagnetic ordering. This article aims to provide an overview of the current research and potential future directions in the field of antiferromagnetic insulatronics.

You can find the publication under Appl. Phys. Lett. 122, 080502 (2023).

A joint publication with Jairo Sinova and Libor Šmejkal about the growth pathways and structural properties of the manganese silicides has been published in Physical Review Materials.

They describe that the magnetically ordered phases of the ${\mathrm{Mn}}_5{\mathrm{Si}}_3$ crystal are proving to be prototypes for the study of the new fundamental spin physics related to the spontaneous breaking of the time-reversal symmetry despite a zero net magnetization. Here, they report on a route to grow epitaxial ${\mathrm{Mn}}_5{\mathrm{Si}}_3$ thin films on Si(111). The growth pathways and structural properties of the manganese silicides can be rationalized in terms of reactions maximizing the free-energy lowering rate. Moreover, they found that the magnetic and the magnetotransport properties can be used as an efficient tool to track both ${\mathrm{Mn}}_5{\mathrm{Si}}_3$ crystallinity and proportion in the deposited layers.

You can find the publication under Phys. Rev. Materials 7, 024416 (2023).