Origin of magnetoresistance in Ca: doped YIG

In order to find a microscopic origin of a strong anisotropy, shown by the magnetoresistance in Ca: doped YIG, we investigate a simple system of two hybridizing iron–oxygen clusters with tetrahedral and octahedral symmetries, respectively. By applying a group-theoretical approach to the diagonalization of the Hubbard model with the Zeeman term included, we obtain energy levels and the orbital eigen-states for both the clusters. This is the point of departure for calculating the total probability of the charge transfer between the clusters. And, finally, the magnetoresistance, as a function of the external field, is found at room temperatures. As an origin of the anisotropy in the magnetoresistance, we suggest the symmetry of the orbital eigen-states of the clusters, which finds its reflection in a form of the orbital contribution to the magnetic moments of the clusters.