Remanent Magnetization of Ferromagnetic Single Crystal

Abstract

The field dependence of thermo-remanent magnetization (TRM) and isothermal remanent magnetization (IRM) of single crystals of ferromagnetic substances such as natural samples of hematite, pyrrhotite, and magnetite and synthetic samples of orthoferrite (YFeO₃), magnesioferrite (MgFe₂O₄), and yttrium iron garnet (YIG) was studied.
It was confirmed for all the specimens that the characteristics of TRM are kept in their fairly large single crystals. The production of TRM was most effective in those crystals having strong magnetic anisotropy, especially in parasitic ferromagnetic substances such as hematite and YFeO₃, for which an applied magnetic field of only several Oersteds is strong enough to produce almost saturated TRM. The saturation value of TRM is nearly the same as its spontaneous magnetization. For cubic crystals such as magnetite, magnesioferrite and YIG, the value of J_Tc/J_s, which may represent a degree of fixing of TRM, was only 10^-3 at most, though TRM was definitely distinguished from IRM even in this case. Anisotropy of remanent magnetization into various crystal axes was also examined for every specimen.
These experimental results may be interpreted as follows. In the case of a single crystal carefully prepared the acquisition of TRM is subject mostly to the magnetocrystalline anisotropy. The larger the magnetocrystalline anisotropy is and the smaller the spontaneous magnetization is, the larger becomes the intensity of TRM.
Structures of magnetic domains of magnesioferrite in various stages of magnetization were observed with the aid of the Faraday effect in order to study the fixing mechanism of TRM.