Dimensionality of a system of exchange-coupled grains and magnetic properties of nanocrystalline and amorphous ferromagnets

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Abstract
Characteristics of random magnetic anisotropy in ferromagnetic films of amorphous Co90P10 and nanocrystalline Ni75C25, Fe80B4C16, and Co80C20 alloys and also in multilayer films [Co93P7(x)/Pd(14 Å)]20 and [Co90P10(x)/Pd(14 Å)]20 obtained by various technological procedures were studied experimentally. It was found that the spatial dimensionality (d) of the system of ferromagnetically coupled grains (2Rc) in the materials under study determined the exponent in the power dependence of the approach of magnetization to saturation in the region of fields HA/MRc2. The dependence ΔM∼H−1/2 was observed for nanocrystalline and amorphous films with a three-dimensional grain arrangement. The approach to saturation in multilayer films with a two-dimensional grain arrangement in an individual magnetic layer follows the law ΔM∼H−1. The main micromagnetic characteristics of random anisotropy, such as the ferromagnetic correlation radius Rf and the average anisotropy 〈K〉 of a ferromagnetic domain with a size of 2Rf, were determined for multilayer Co/Pd films. Correlation was found between the coercive field and these characteristics of random anisotropy.