Curietemperatur und Kollektivmagnetisierung bei ein- und vielkristallinen dünnen Nickelschichten

Abstract

With a method of observing the temperature dependence of therf-permeability the Curie temperatureΘ of evaporated thin films (thicknessD from 30 to 300 Å) of nickel with various structures was investigated.

Monocrystalline samples withD about 50 Å showedΘ-values comparable to the bulk material.

The behaviour of some polycrystalline and several granulated films depends to a large extent on the structure (varied by conditions of deposition). It may be explained with a model that treats aggregates of small ferromagnetic particles with a high spontaneous magnetization but an interaction that may be considerably weaker than the full ferromagnetic exchange coupling. There appears a transition (to superparamagnetism) temperatureT _A which can be much lower than the Curie temperature. The expected dependence of T_A on particle size fits approximately with the experimental results from therf-method and electron diffraction data at samples of various structures.