Observation of temperature-dependent Dzyaloshinskii–Moriya interaction within the 50–300 K range

The Dzyaloshinskii–Moriya interaction (DMI) is essential for the formation of chiral objects in magnetic heterostructures. Herein, the temperature (T)-dependence of the DMI in Pt/Co/MgO is investigated over a wide range below 300 K. The T-dependent behavior of the DMI is stronger than that of the Heisenberg exchange interaction; thus, the anisotropic exchange is more T-sensitive than the isotropic exchange. Additionally, D∝M4.79 and A∝M2 for Pt/Co/MgO, and different ferromagnet (FM) layers can originate from different scaling factors between D and M. Therefore, the DMI T-dependence in a Pt-based multilayer system depends on the FM type, which implies that orbital hybridization at an interface may elucidate the relation between D and M.

Field-tunable toroidal moment in a chiral-lattice magnet

Ferrotoroidal order, which represents a spontaneous arrangement of toroidal moments, has recently been found in a few linear magnetoelectric materials. However, tuning toroidal moments in these materials is challenging. Here, we report switching between ferritoroidal and ferrotoroidal phases by a small magnetic field, in a chiral triangular-lattice magnet BaCoSiO4 with tri-spin vortices. Upon applying a magnetic field, we observe multi-stair metamagnetic transitions, characterized by equidistant steps in the net magnetic and toroidal moments. This highly unusual ferri-ferroic order appears to come as a result of an unusual hierarchy of frustrated isotropic exchange couplings revealed by first principle calculations, and the antisymmetric exchange interactions driven by the structural chirality. In contrast to the previously known toroidal materials identified via a linear magnetoelectric effect, BaCoSiO4 is a qualitatively new multiferroic with an unusual coupling between several different orders, and opens up new avenues for realizing easily tunable toroidal orders.

Isotropic Nature of the Metallic Kagome Ferromagnet Fe3Sn2 at High Temperatures

Anisotropy and competing exchange interactions have emerged as two central ingredients needed for centrosymmetric materials to exhibit topological spin textures. Fe3Sn2 is thought to have these ingredients as well, as it has recently been discovered to host room temperature skyrmionic bubbles with an accompanying topological Hall effect. We present small-angle inelastic neutron scattering measurements that unambiguously show that Fe3Sn2 is an isotropic ferromagnet below TC≈660 K to at least 480 K—the lower temperature threshold of our experimental configuration. Fe3Sn2 is known to have competing magnetic exchange interactions, correlated electron behavior, weak magnetocrystalline anisotropy, and lattice (spatial) anisotropy; all of these features are thought to play a role in stabilizing skyrmions in centrosymmetric systems. Our results reveal that at the elevated temperatures measured, there is an absence of significant magnetocrystalline anisotropy and that the system behaves as a nearly ideal isotropic exchange interaction ferromagnet, with a spin stiffness D(T=480 K)=168 meV Å2, which extrapolates to a ground state spin stiffness D(T=0 K)=231 meV Å2.

Observation and deconvolution of a unique EPR signal from two cocrystallized spin triangles

A 16-line pattern has been theoretically predicted, but hitherto not reported, for the Electron Paramagnetic Resonance (EPR) spectrum of antiferromagnetically coupled CuII triangles experiencing isotropic exchange of isosceles magnetic symmetry....

Single Chiral Skyrmions in Ultrathin Magnetic Films

The stability and sizes of chiral skyrmions in ultrathin magnetic films are calculated accounting for the isotropic exchange, Dzyaloshinskii–Moriya exchange interaction (DMI), and out-of-plane magnetic anisotropy within micromagnetic approach. Bloch skyrmions in ultrathin magnetic films with B20 cubic crystal structure (MnSi, FeGe) and Neel skyrmions in ultrathin films and multilayers Co/X (X = Ir, Pd, Pt) are considered. The generalized DeBonte ansatz is used to describe the inhomogeneous skyrmion magnetization. The single skyrmion metastability/instability area, skyrmion radius, and skyrmion width are found analytically as a function of DMI strength d . It is shown that the single chiral skyrmions are metastable in infinite magnetic films below a critical value of DMI d c , and do not exist at d > d c . The calculated skyrmion radius increases as d increases and diverges at d → d c − 0 , whereas the skyrmion width increases monotonically as d increases up to d c without any singularities. The calculated skyrmion width is essentially smaller than the one calculated within the generalized domain wall model.

Some new trends in the design of single molecule magnets

In this review we briefly discuss some new trends in the design of single molecule magnets based on transition (3d, 4d, 5d) and rare-earth (4f) metal ions. Within this broad theme the emphasis of the present review is placed on the molecules which exhibit strong magnetic anisotropy originating from the unquenched orbital angular momenta in the ground orbitally degenerate (or quasi-degenerate) states. Along with the general concepts we consider selected examples of the systems comprising orbitally-degenerate metal ions and demonstrate how one can benefit from strong single-ion anisotropy arising from the first-order orbital angular momentum. The role of crystal fields, spin-orbit coupling and structural factors is discussed. Some observation stemming from the analysis of the isotropic exchange interactions, magnetic anisotropy and strongly anisotropic orbitally-dependent superexchange are summarized as guiding rules for the controlled design of single molecule magnets exhibiting high barriers for magnetization reversal and, consequently, high blocking temperatures.