Effects of Pressure on the Magnetization of Ferrites: Anomalies Due to Strain-Induced Anisotropy in Porous Samples

Anomalously large changes in the magnetization as a function of hydrostatically applied pressure have been observed over a range of sample densities and applied fields in porous polycrystalline (ceramic) ferrites such as NiFe2O4 and YIG. These changes can be explained on the basis of anisotropy energy resulting from nonisotropic strain. The experimental results show that large nonisotropic strains can obtain in porous samples and thus, care must be exercised in interpreting ``hydrostatic'' measurements on porous materials especially when the property being measured is known to be strongly dependent on the nature of the induced strain. For single-crystal YIG, the saturation magnetization per unit mass is found to be independent of pressure as is expected since its magnetic moment is the spin-only value.