Tuning magnetic coercivity with external pressure in iron-rhenium based ferrimagnetic double perovskites

Abstract

We studied the effect of physical pressure on the electronic and magnetic properties of ferrimagnetic double perovskites ${A}_{2}{\mathrm{FeReO}}_{6}$ ($A=\mathrm{Ca}$, Ba) using Re ${L}_{2,3}$ edge x-ray absorption spectroscopy and powder diffraction measurements. Volume compression is shown to dramatically increase the magnetic coercivity (${H}_{c}$) in polycrystalline samples of both compounds with $\mathrm{\ensuremath{\Delta}}{H}_{c}/\mathrm{\ensuremath{\Delta}}V\ensuremath{\sim}150$--200 $\mathrm{Oe}/{\AA{}}^{3}$. A nearly eight-fold increase in ${H}_{c}$, from 0.2 to 1.55 T, is obtained in ${\mathrm{Ba}}_{2}{\mathrm{FeReO}}_{6}$ at $P=29$ GPa. While no signs of structural phase transitions are seen in either sample to $\ensuremath{\sim}30$ GPa, the structural data points to a pressure-driven increase in tetragonal distortion of ${\mathrm{ReO}}_{6}$ octahedra. A sizable but pressure-independent Re orbital-to-spin magnetic moment ratio is observed, pointing to the critical role of spin-orbit interactions at Re sites. We present a ${j}_{\mathrm{eff}}$ description of the electronic structure that combines effects of crystal field and spin-orbit coupling on the Re $5{d}^{2}$ orbitals and use this description to provide insight into the pressure-induced enhancement of magnetic anisotropy.