Magnetization Dependence on Temperature and Grain Size in Nanostructured Samples

Abstract

We report on the low temperature thermal demagnetization phenomenology taking place in samples having different nanostructures. Those samples were prepared by crystallization, starting from a melt spun FeCoSiBC amorphous precursor and following two different routes: i) conventional thermal treatments carried out at different temperatures and ii) high energy ball milling. According to XRD results the average grain size of the crystallized samples increased from 7 nm (milled sample) up to 110 nm (sample treated at the highest temperature). The measurement of the temperature dependence of the magnetization (carried out by means of a SQUID magnetometer in a temperature range going from 1.7 K up to 200 K) revealed a remarkable influence of the average grain size on the thermal demagnetization. Our results were analyzed in terms of the predictions of different models of ferromagnetism and allowed us to conclude that, i) our samples behaved as weak ferromagnets with a nanostructure dependent spin wave spectrum and ii) the single particle-type excitations play a measurable role on the thermal demagnetization of the samples.