Mössbauer studies of the surface and bulk properties of substituted iron-garnet films in the vicinity of the Curie point

The magnetic properties of the surface layer and bulk of iron-garnet films of composition Y_2.6Sm_0.4Fe_3.7Ga_1.3O₁₂, grown by liquid-phase epitaxy on substrates of a gadolinium-gallium garnet single crystal, are investigated. The method of simultaneous gamma-ray, x-ray, and electron Mössbauer spectroscopy is used for the investigations. It is found that the temperature T _c(L) of the transition to the paramagnetic state of a thin layer localized at a depth L below the surface within ～300 nm decreases smoothly with decreasing distance from the surface. The causes of the difference between the temperature of the transition to the paramagnetic state in the surface layer and that bulk of the film are: 1) variation of the degree of substitution of gallium for iron in the surface layer; 2) weakening of exchange interactions at the surface of the sample.