Magnetic properties of sputtered Bi3Fe5O12

A series of Bi-substituted yttrium-iron-garnet films were grown including its end members, YIG and BiIG, by an RF-diode sputtering method. The low-temperature magnetization of highly Bi-substituted garnet is much lower than expected from the linear expansion of the lattice. The temperature dependence of the magnetization of these materials is described by a molecular field model in which some of the moment on the tetrahedral site Fe³⁺ ion is assumed to be transferred to the Bi³⁺ ion on the dodecahedral site. The proposed model contains three sublattices: Fe³⁺ ion at the octahedral site, Fe³⁺ with reduced spin at the tetrahedral site, and partially spin polarized Bi³⁺ ions at the dodecahedral sites. Reasonable agreement between the model and data is obtained for BiIG if it is assumed that the spin on the tetrahedral iron sublattice is reduced by 0.5 μ_B and the Bi ion has a moment of 0.2 μ_B which is strongly coupled to the iron sublattice. The large values of the uniaxial anisotropy energy, the crystalline anisotropy energy, and the linewidths measured by ferromagnetic resonance are complementary to this result