We report a comprehensive study of the temperature evolution of in-plane (IP) and out-of-plane (OOP) effective magnetic anisotropies in compensated ferrimagnetic ${\mathrm{Fe}}_{100-x}{\mathrm{Gd}}_x$ alloy films by employing direct current magnetometry and radiofrequency (RF) transverse susceptibility (TS) measurements. We suggest that our ${\mathrm{Fe}}_{100-x}{\mathrm{Gd}}_x$ system is chemically inhomogeneous and phase segregates into Fe- and Gd-enriched regions. Our IP and OOP magnetometry results indicate that the system undergoes a temperature-driven transformation from an IP-spin-configuration-dominated state to an OOP-spin-configuration-dominated state below a certain temperature (spin reorientation temperature). A two-step reversal behavior emerges in the OOP $M$($H$) loop near compensation, which we attribute to the sequential magnetization reversals of Fe- and Gd-enriched domains. Field-induced spin-flop transitions were also observed near the compensation. Our RF TS measurements indicate that the effective magnetic anisotropy for the OOP configuration dominates over that for the IP configuration below a certain spin reorientation temperature. Both IP and OOP anisotropy fields determined from our TS measurement exhibit a minimum around the compensation temperature, which has been explained in the framework of the Stoner-Wohlfarth model.

In magnetic trilayer systems, spin pumping is generally addressed as a reciprocal mechanism characterized by one unique spin-mixing conductance common to both interfaces. However, this assumption is questionable in cases where different types of interfaces are present. Here, we present a general theory for analyzing spin pumping in cases with more than one unique interface and where the magnetic coupling is allowed to be noncollinear. The theory is applied to analyze layer-resolved ferromagnetic resonance experiments on the trilayer system ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/{\mathrm{Ru}/\mathrm{Fe}}_{49}{\mathrm{Co}}_{49}{\mathrm{V}}_2$ where the Ru spacer thickness is varied to tune the indirect exchange coupling. It is demonstrated that the equation of motion of macrospins driven by spin pumping need to be modified in case of noncollinear coupling. Our analysis also shows that the spin pumping in trilayer systems with dissimilar magnetic layers, in general, is nonreciprocal.

We quantify the presence of spin-mixed states in ferromagnetic 3D transition metals by precise measurement of the orbital moment. While central to phenomena such as Elliot-Yafet scattering, quantification of the spin-mixing parameter has hitherto been confined to theoretical calculations. We demonstrate that this information is also available by experimental means. Comparison of ferromagnetic resonance spectroscopy with x-ray magnetic circular dichroism results show that Kittel’s original derivation of the spectroscopic $g$ factor requires modification, to include spin mixing of valence band states. Our results are supported by ab initio relativistic electronic structure theory.

Here we demonstrate an experimental observation of GHz-scale spin dynamics resolved to sublattice octahedral ($O_h$) tetrahedral ($T_d$) sites in a spinel ferrimagnet, in this case a Mn-ferrite thin film. X-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) are used, in combination with multiplet calculations, to uniquely identify the spectral signature from ${\mathrm{Mn}}^{2+}$ and ${\mathrm{Fe}}^{2+,3+}$ on $O_h$ and $T_d$ lattice sites. With the sample under $\mathit{rf}$ excitation, the spin alignment of the sublattices is tracked with time-resolved XMCD (TR-XMCD). The spin alignment of the sublattices is mostly antiferromagnetic. The phase difference between the $O_h {\mathrm{Fe}}^{2+}$ [$O_h {\mathrm{Fe}}^{3+}$] and $T_d {\mathrm{Mn}}^{2+}$ sites is $181.2\pm 3.8^{\circ }$ [$183.3^{\circ }\pm 3.7^{\circ }$] at 150 K and $186.6\pm 2.2^{\circ }$ [$182.0^{\circ }\pm 2.2^{\circ }$] at 300 K. Such direct measurement of the dynamic coupling, exchange stiffness, and damping enabled by TR-XMCD across sublattices will be essential for optimizing the development of future-generation microwave devices.