High-Field Magnetization Curve of Porous Polycrystalline YIG

Abstract

The magnetization has been measured as a function of magnetic field strength on porous polycrystalline YIG (porosities up to 27.1%). Measurements on spherical samples were done with a vibrating sample magnetometer at internal fields between 30 Oe and 9 kOe, on toroidal samples at fields up to 50 Oe. The results agree with an extension of Néel's theory, not only at high field strength but down to the remanence point. In the extended theory the influence of the exchange interaction has been taken into account. This refinement of the theory is essential for obtaining agreement with the experimental data at relatively low magnetic fields (below 50 Oe), but of little consequence at higher fields. From a comparison of the experimental data with the theory, we infer the mean‐squares deviation of the local saturation magnetization from its average. The values obtained agree well with values deduced from measurements of the longitudinal susceptibility at microwave frequencies. The analysis of the data also indicates that the materials investigated contain inclusions of a secondary magnetic phase (approximately 1% magnetite) in addition to pores.