Strain-dependent, Extraordinary Magnetocrystalline Anisotropy in Sr$_{2}$CrReO$_{6}$ Epitaxial Films

We have grown Sr$_{2}$CrReO$_{6}$ films that exhibit one of the largest anisotropy fields shown to date (18.1 T) and a large uniaxial magnetocrystalline anisotropy energy $K_{u} =$ 9.05 $\times$ 10$^{6}$ erg/cm$^{3}$. We investigate strain-controlled magnetocrystalline anisotropy for epitaxial Sr$_{2}$CrReO$_{6}$ films grown on (LaAlO$_{3})_{0.3}$(Sr$_{2}$AlTaO$_{6})_{0.7}$, SrTiO$_{3}$ and Sr$_{2}$CrNbO$_{6}$/LSAT substrates using high resolution X-ray diffraction, in-plane and out-of-plane superconducting quantum interference device magnetometry, and density functional theory calculations. The substrates impose tetragonal distortions of $c$/$a =$ 1.025, 1.007 and 0.991, respectively, which lead to dramatic changes in magnetocrystalline anisotropy of order tens of tesla and a switching of the magnetic easy axis from in-plane for compressive strain to out-of-plane for tensile strain, as observed via magnetometry measurements. Density functional theory calculations elucidate the dependence of oxygen octahedra tilting and rotation on tetragonal distortions, which affect both electronic and magnetic properties of the films. Finally, X-ray magnetic circular dichroism measurements reveal strong magnetic moment contributions at the oxygen sites, as evident in oxygen-specific X-ray absorption spectra.