Origin of the noncubic anisotropy in Mn∶ (Y, Gd)3Fe5O12 thin films

Thin Mn∶ YIG films exhibit a large noncubic anisotropy. We show that this anisotropy may be understood on the basis of a strong Jahn-Teller effect of octahedrally coordinated Mn3+ ions. The corresponding mechanism is simple — the strain caused by the film/substrate misfit orders the local Jahn-Teller distortions and, as a consequence, noncubic anisotropy appears. In particular, due to the nonparallel local coordinate systems of octahedral sites, an uniaxial anisotropy is predicted also for the (111) growth plane. It is pointed out that the interaction between the Jahn-Teller centres and/or their interaction with the lattice defects lower the magnitude of the anisotropy.