Direct observation of symmetry-specific precession in a ferrimagnet

Abstract

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 $181.2\ifmmode\pm\else\textpm\fi{}3.{8}^{\ensuremath{\circ}}$ [$183.{3}^{\ensuremath{\circ}}\ifmmode\pm\else\textpm\fi{}3.{7}^{\ensuremath{\circ}}$] at 150 K and $186.6\ifmmode\pm\else\textpm\fi{}2.{2}^{\ensuremath{\circ}}$ [$182.{0}^{\ensuremath{\circ}}\ifmmode\pm\else\textpm\fi{}2.{2}^{\ensuremath{\circ}}$] 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.