Ferrimagnetism in ${\mathrm{EuFe}}_4{\mathrm{Sb}}_{12}$ due to the Interplay of $f$-Electron Moments and a Nearly Ferromagnetic Host

We combine x-ray magnetic circular dichroism spectroscopy at Fe $L_{2,3}$ edges, at Eu $M_{4,5}$ edges, x-ray absorption spectroscopy (XAS) investigation of Eu valence, and local spin density calculations, to show that the filled skutterudite ${\mathrm{Eu}}_{0.95}{\mathrm{Fe}}_4{\mathrm{Sb}}_{12}$ is a ferrimagnet in which the Fe $3d$ moment and the ${\mathrm{Eu}}^{2+}$ $4f$ moment are magnetically ordered with dominant antiferromagnetic coupling. From Eu $L_3$ edge XAS, we find that about 13% of the Eu have a formal valence of $3+$. We ascribe the origin of ferrimagnetism at a relatively high transition temperature $T_C$ of 85 K in ${\mathrm{Eu}}_{0.95}{\mathrm{Fe}}_4{\mathrm{Sb}}_{12}$ to $f$-electron interaction with the nearly ferromagnetic $[{\mathrm{Fe}}_4{\mathrm{Sb}}_{12}{]}^{2.2-}$ host lattice.

Figure 1

(a) Magnetization vs field at 5 K in ${\mathrm{Eu}}_{0.95}{\mathrm{Fe}}_4{\mathrm{Sb}}_{12}$. Inset shows ${\chi }^{-1}$ vs $T$. (b) Eu $L_3$ edge XAS with a fit described in the text.

Figure 2

Eu $M_{4,5}$ edge (a) XAS and (b) XMCD in ${\mathrm{Eu}}_{0.95}{\mathrm{Fe}}_4{\mathrm{Sb}}_{12}$ measured in a field of 2 Tesla at 4.8 K. (c) Theoretical fit to Eu $M_4$ XAS. (d) Lorentzian fit to the $M_5$ edge XMCD data. Inset in (b) shows the hysteresis of $M_5$ edge XMCD peak intensity at $E=1128\mathrm{eV}$ at 4.8 K.

Figure 3

Fe $L_{2,3}$ edge (a) XAS and (b) XMCD in ${\mathrm{Eu}}_{0.95}{\mathrm{Fe}}_4{\mathrm{Sb}}_{12}$ showing that Fe is magnetically ordered.

Figure 4

(a) Electronic density of states and projections onto the sphere of Fe $d$ and Eu $f$ character, for magnetic ${\mathrm{EuFe}}_4{\mathrm{Sb}}_{12}$ on a per formula unit basis. Note that the narrow Eu $f$ peaks are cut off by the scale. Majority spin is shown above the axis, and minority below. $E_F$ is at 0 eV. (b) Calculated difference of Fe $2p$ XAS into spin up and spin down components with a 0.1 eV broadening.