Effect of structural distortion on ferrimagnetic order in Lu1-xLxFe2O4 (L=Y and Er; x=0.0, 0.1, and 0.5)

We have studied the correlation between the structural distortion and the magnetic interaction change in the ferrimagnetic (Lu, L)Fe2O4 (L=Y and Er) by using neutron powder diffraction and x-ray magnetic circular dichroism (XMCD). The Rietveld profile refinements revealed that the Y or Er substitution flattens the hexagonal unit cell of the system and asymmetrically distorts the bipyramidal FeO5 cages with the increase in the substitution. Even in the presence of the Y or Er substitution, root 3 x root 3 superlattices are formed by Fe-valence ordering, and the interlayer magnetic coupling behavior does not change very much. Meanwhile, the Fe 2p XMCD spectra indicate that the Fe3+ spins become frustrated as the substitution increases. These results support that the unquenched orbital moment of the Fe2+ ions is the dominant factor for the giant magnetic anisotropy in LuFe2O4.