Estudo do efeito magnetocalórico em amorfos

Abstract

The development of theoretical models to adequately describe the magnetocaloric effects (MCE) is important both for explaining the experimental responses presented so far and for predicting new and unexpected trends. Among the various materials, the class of amorphous materials presents characteristics that enhance the MCE, such as high refrigeration capacity. In this thesis, a theoretical description of the magnetocaloric effect in amorphous systems will be presented, considering the nature of magnetic interactions and the distribution of magnetic moments through the Handrish-Kobe approximation for systems with isotropic magnetization and the HPZ approximation for anisotropic ones. These models were applied to three distinct families: the first with only one magneticnet work, the second with two networks with isotropic magnetization, and the third with two networks with high anisotropy. Thus, in the amorphous compounds of the Gd1−xNixseries, the influence of magnetic interactions and the amorphization term on the magnetocaloric effect was analyzed. For the materials of the Gd55FexAl45−xseries, the influence of the Fe/Al ratio, the magnetocaloric interaction, and the amorphization terms on the respective arrangements were verified. Finally, for the amorphous ErxFe1−x, the influence of anisotropy and the competition between it and the magnetic interactions were analyzed through a systematic study. Therefore, a methodology for obtaining the magnetization of amorphous systems was presented, allowing for the study of the anisotropic magneto-caloric effect of ferromagnetic and ferrimagnetic nature.