First Principle Study of Magnetism and Magneto-structural Coupling in Gallium Ferrite

ABSTRACT

We report a first-principles study of the magnetic properties, site disorder and magneto-structural coupling in multiferroic gallium ferrite (GFO) using local spin density approximation (LSDA+U) of density functional theory. The calculations of the ground state A-type antiferromagnetic structure predict magnetic moments consistent with the experiments whilst consideration of spin-orbit coupling yields a net orbital moment of ~ 0.025μB/Fe site also in good accordance with the experiments. We find that though site disorder is not spontaneous in the ground state, interchange between Fe2 and Ga2 sites is most favored in the disordered state. The results show that ferrimagnetism in GFO is due to Ga-Fe site disordering such that Fe spins at Ga1 and Ga2 sites are antiferromagnetically aligned while maintaining ferromagnetic coupling  between Fe spins at Ga1 and Fe1 sites as well as between Fe spins at Ga2 and Fe2 sites. The effect of spin configuration on the structural  distortion clearly indicates presence of magneto-structural coupling in GFO. 

...we started our calculation to determine the ground state structure of  GFO with four possible antiferromagnetic spin structures, namely, AFM1 (A-type antiferromagnetic) ,AFM-2   (C-type antiferromagnetic), AFM-3 (G-type antiferromagnetic ) and AFM-4 and established that the ground state magnetic structure of GFO is A-type antiferromagnetic (A-AFM) [23]. 

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http://arxiv.org/ftp/arxiv/papers/1108/1108.2773.pdf