Pressure Dependence of the Microwave Resonance Properties of Some Spinel and Garnet Ferrites

The anisotropy field, g value, and linewidth of several spinel and garnet ferrites have been measured at X band and room temperature as functions of hydrostatic pressure to 10⁴ kg/cm². The crystals studied include yttrium, ytterbium, and erbium iron garnet; magnesium ferrite (with different distributions of Mg²⁺ ions on A and B sites); and Ni_1-zCozFe₂O₄ with z=0, 0.05 and 0.10. The pressure dependence of magnetization was measured using magnetostatic mode methods in the narrow linewidth materials, yttrium iron garnet and magnesium ferrite.The complexity of the crystal structure and magnetic interactions makes any quantitative interpretation very difficult. However, the observations can be understood qualitatively in terms of the volume dependence of the crystalline fields and the exchange interactions. In the case of erbium iron garnet, the volume dependence of the ferric-rare-earth exchange constant is calculated; and, in the case of nickel cobalt ferrite, a simple explanation is offered for the observed volume dependence of the Co²⁺ anisotropy.The contribution of thermal lattice vibrations to the linewidth in yttrium iron garnet is discussed, and the possibility of an anisotropic spin-orbit interaction is considered.