Exchange Resonances in Gadolinium Iron Garnet near the Magnetic Compensation Temperature

The theory of ferrimagnetic resonance in a system of two sublattices is reviewed with emphasis upon the behavior near the compensation point. Experimental studies have been made on the gadolinium-iron garnet system in a temperature region of about 30°C which included the compensation point. The “normal” and “exchange” modes were observed and their field dependence upon temperature above and below compensation was found to be in good agreement with that predicted. From the data near compensation it was possible to derive values for the effective field acting on the gadolinium sublattice at compensation, for the difference in gyromagnetic ratios of the iron and gadolinium sublattices, and for the sum of the anisotropy fields on the latter. Microwave evidence is presented for the existence of antiferromagnetic domains at the compensation temperature.