Microwave Absorption near the Reorientation Temperature in Rare Earth Orthoferrites

Abstract

Studies have been made on Tm, Er, and Ho rare earth orthoferrites in their spin-reorientation temperature ranges in an attempt to observe magnetic resonance. Magnetic loss peaks sharp with dc field H and temperature T (at constant H) have been observed. They form two well-defined linear branches when H at a loss peak is plotted vs T. One branch has H ∥ a and hrf ∥ c, and the other has H ∥ c and hrf ∥ a. In TmFeO3 the former branch extends from 82°K where H=0, to 86°K where H=7000 Oe (the maximum field available). The latter branch extends from 93°K where H=0 to 82.5°K where H=7000 Oe. The two branches thus cross each other. A remarkable feature is the almost complete lack of frequency dependence of the two branches from 5 to 54 000 MHz. Torque and magnetization measurements have shown that the two temperatures of the peaks for H=0 are essentially the same as the end temperatures of the spin reorientation range. It is proposed, preliminarily, that the loss peaks are associated with a maximum in the susceptibility which occurs when H is just large enough to pull the net moment parallel to the a or c axis.