Effects of Structural Distortion Induced by Sc Substitution in LuFe${}_2$O${}_4$

We have studied the correlation between the structural distortion and the electronic/magnetic properties in single-crystalline (Lu,Sc)Fe${}_2$O${}_4$ (Sc=0.05 and 0.3) by using X-ray diffraction (XRD), magnetic susceptibility, and X-ray absorption spectroscopy (XAS)/x-ray magnetic circular dichroism (XMCD)measurements. The Rietveld structure analysis of the XRD patterns revealed that the Sc substitution induced an elongation of the FeO${}_5$ bipyramidal cages in LuFe${}_2$O${}_4$ and increased the Fe${}_2$O${}_4$ bilayer thickness. A non-negligible decrease in the ferrimagnetic transition temperature T${}_C$ is observed in the magnetic susceptibility curve of the Sc=0.3 sample, but the XAS/XMCD spectra do not show any difference except for a small reduction of dichroism signals at the Fe${}^{3+}$ absorption edge. We interpret this suppression of T${}_C$ to be the result of a decreased spin-orbit coupling effect in the Fe${}^{2+}$ $e_{1g}$ doublet under $D_{3h}$ symmetry, which is induced by the weakened structural asymmetry of the FeO${}_5$ bipyramids.