Thermogravimetric measurements of thin iron films magnetization near their Curie temperature

Abstract

One of the important problems in bulk ferromagnetism is still the determination of magnetization as a function of temperature. The problem becomes more complicated when one tries to explain the magnetization of thin films near Tc. The experimental situation is far from clear, mainly because the experiments are difficult to perform. We have implemented a thermogravimetric technique using a modern microbalance to determine the magnetization behavior of thin films of pure Fe near Tc. We are able to obtain very precisely the films’ magnetization, by measuring the force exerted over the films when they are imbedded in a fixed external magnetic field, with this technique. We prepared several samples of pure Fe films, evaporated in ultrahigh vacuum conditions onto Cu foils ranging in thickness between 50 and 300 nm and measured their magnetization near the critical point. The value of the Tc of the films is systematically lowered from the bulk Tc, being 342 K lower for the 50 nm films. The magnetization curves show a dependence on the temperature as a series containing terms in (T/Tc)3/2, (T/Tc)5/2, and (T/Tc)7/2 at temperatures low compared with Tc. Near Tc, the magnetization decreases linearly on temperature for films of all thicknesses.