Year: 2023

A joint publication with Jairo Sinova and Libor Šmejkal about crystal magnons in altermagnets has been published in Physical Review Letters.

They theoretically demonstrate a new class of magnons on a prototypical d-wave altermagnet
RuO2 with the compensated antiparallel magnetic order in the ground state. Based on density-functional-theory calculations they observe that the THz-range magnon bands in RuO2 have an alternating chirality splitting, similar to the alternating spin splitting of the electronic bands, and a linear magnon dispersion near the zero wave vector. They also show that, overall, the Landau damping of this metallic altermagnet is suppressed due to the spin-split electronic structure, as compared to an artificial antiferromagnetic phase of the same RuO2 crystal with spin-degenerate electronic bands and chirality-degenerate magnon bands.

A joint publication with Libor Šmejkal and Rafeal González-Hernández about the Anomalous Hall Effect in in doped AgCrSe2 has been published in Advanced Science.

They report the observation of a spontaneous AHE in doped AgCrSe2, a layered polar semiconductor with an antiferromagnetic coupling between Cr spins in adjacent layers. The anomalous Hall resistivity is comparable to the largest observed in compensated magnetic systems to date, and is rapidly switched off when the angle of an applied magnetic field is rotated to ≈80° from the crystalline c-axis. The ionic gating experiments show that the anomalous Hall conductivity magnitude can be enhanced by modulating the p-type carrier density. They also present theoretical results that suggest the AHE is driven by Berry curvature due to noncollinear antiferromagnetic correlations among Cr spins, which are consistent with the previously suggested magnetic ordering in AgCrSe2. Their results open the possibility to study the interplay of magnetic and ferroelectric-like responses in this fascinating class of materials.

A joint publication with Jairo Sinova and Libor Šmejkal about the influence of magnetism, strain, and pressure on the band topology of EuCd2As2 has been published in Physical Review B.

They analyze the role of the delicate interplay of Eu magnetism, strain, and pressure on the realization of nontrivial topological phases. For that they invoke a combination of a group theoretical analysis with ab initio density functional theory calculations and uncover a rich phase diagram with various nontrivial topological phases beyond a Weyl semimetallic state, such as axion and topological crystalline insulating phases, and discuss their realization.

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.