Untersuchung über Zeiteffekte bei der langsamen Ummagnetisierung dünner polykristalliner Nickelschichten

Abstract

Magnetization reversals under the influence of different but each time constant external magnetic fields have been observed by means of the Faraday effect in the range of measuring time between 10 sec and 10⁵ sec. The samples consisted of nickel thin films, which have been condensed onto glass substrates at temperatures of 200 and 360°C.

An increase of time effects has been observed with decreasing film thickness and/or reduction of the average crystallite size of the samples. This may be attributed to thermal fluctuation effects. Additionally they explain the disappearing of hysteresis at granulated samples of very small average thickness, which reach (thermal) equilibrium during the measuring time and in this regard may be considered as a transition toward superparamagnetism.

A comparison of the measured time effects with fluctuation theory for a collective of independently and simultaneously activable individual processes indicates that a mechanism with an interaction (at least between neighboring crystallites) must be considered.