In order to rationalize and predict the behavior of compounds containing 5d transition metal ions, an understanding of the local moments and superexchange interactions from which their magnetic properties are derived is necessary. The magnetic and electrical properties of the ferrimagnetic double perovskites Ca2CoOsO6 and Ca2NiOsO6 studied here provide critical insight toward that goal. First-principles density functional theory (DFT) calculations indicate, and experimental measurements confirm, that the Os­(VI) moments are directed antiparallel to the Co/Ni moments. X-ray magnetic circular dichroism (XMCD) measurements reveal that the orbital moment on osmium has a magnitude that is approximately 30% of the spin moment, and the two contributions oppose each other. Both the size and direction of the orbital moment are confirmed by the DFT calculations. The size of the Os­(VI) total moment is predicted to be 0.6–0.7 μB by DFT calculations. The ferrimagnetic ground state is stabilized by strong antiferromagnetic coupling between the d2 Os­(VI) ion and the d8/d7 Ni­(II)/Co­(II) ion. Not only does the observation of antiferromagnetic coupling violate the Goodenough–Kanamori rules, but also it is unusual in that it becomes stronger as the Os–O–Co/Ni bond angle decreases. This unusual behavior is shown to arise predominantly from coupling between Os t2g orbitals and Ni/Co eg orbitals, mediated by the intervening oxide ion. We further find that both compounds are spin–orbit assisted Mott insulators.

The coexistence and coupling of ferromagnetic and ferroelectric orders in a single material is crucial for realizing next-generation multifunctional applications. The coexistence of such orders is confirmed at room temperature in epitaxial thin films of BiFe Co O (x ≤ 0.15), which manifests a spin structure change from a low-temperature cycloidal one to a high-temperature collinear one with canted ferromagnetism.

Motivated by the recently observed topological Hall effect in ultra-thin films of SrRuO3 (SRO) grown on the SrTiO3 [001] substrate, we investigate the magnetic ground state and anomalous Hall response of the SRO ultra-thin films by virtue of spin density functional theory (DFT). Our findings reveal that in the monolayer limit of an SRO film, a large energy splitting of Ru-t2g states stabilizes an anti-ferromagnetic (AFM) insulating magnetic ground state. For the AFM ground state, our Berry curvature calculations predict a large anomalous Hall response upon doping. From the systematic symmetry analysis, we uncover that the large anomalous Hall effect arises due to a combination of broken time-reversal and crystal symmetries caused by the arrangement of non-magnetic atoms (Sr and O) in the SRO monolayer. We identify the emergent Hall effect as a clear manifestation of the so-called crystal Hall effect in terminology of Šmejkal et al., Crystal Hall effect in collinear antiferromagnets (2019), and demonstrate that it persists at finite frequencies, which is the manifestation of the crystal magneto-optical effect. Moreover, we find a colossal dependence of the anomalous Hall effect on the degree of crystal symmetry breaking also in ferromagnetic SRO films, which all together points to an alternative explanation of the emergence of the topological Hall effect observed in this type of systems.

Half-metallic magnets with metallic behavior in one spin channel and insulating in the other, have attracted considerable attention due to their potential application possibility. The spin-dependent nature of the carrier scattering due to half-metallic nature of these materials, allows for the resistance to be strongly influenced by the low magnetic field. However, the operating temperatures of such known materials are generally low, opening up the need for half-metallic magnets with high transition temperatures. The double perovskites having general formula A2BB′O6 with alternating ordered arrangement of two transition metal sites, B and B′ offer an attractive possibility in this respect. Here, we consider the case of Sr2CrOsO6, which is a ferrimagnetic insulator with transition temperature (Tc) of 725 K, highest ever known in the oxide family, and show that moderate amount of La and Na doping at Sr site can drive the compound half-metallic with high Tc.

Kagome magnets possess several novel nontrivial topological features owing to the strong correlation between topology and magnetism that extends to their applications in the field of thermoelectricity. Conventional thermoelectric (TE) devices use the Seebeck effect to convert heat into electrical energy. In contrast, transverse thermoelectric devices based on the Nernst effect are attracting recent attention due to their unique transverse geometry, which uses a single material to eliminate the need for a multitude of electrical connections compared to conventional TE devices. Here, a large anomalous transverse thermoelectric effect of ≈2 µV K−1 at room temperature in a kagome antiferromagnet YMn6Sn6 single crystal is obtained. The obtained value is larger than that of state‐of‐the‐art canted antiferromagnetic (AFM) materials and comparable with ferromagnetic systems. The large anomalous Nernst effect (ANE) can be attributed to the net Berry curvature near the Fermi level. Furthermore, the ANE of the AFM YMn6Sn6 exceeds the magnetization scaling relationship of conventional ferromagnets. The results clearly illustrate that AFM material YMn6Sn6 is an ideal topological material for room‐temperature transverse thermoelectric applications.