Some antiferromagnetic resonance measurements in $\alpha$-Fe2O3

Abstract

Millimetre wave antiferromagnetic resonance experiments have been made in α-Fe2O3 using both d.c. and pulsed magnetic fields. Both the weak-ferromagnetic modes above the Morin transition temperature and the usual low-temperature antiferromagnetic resonance were examined. The theoretical expression for the frequency dependence of the low-frequency weak-ferromagnetic mode has been verified up to 40 kG. The angular dependence of this mode at 687 Gc/s shows a departure from theory, however, although lower-frequency measurements do not. The angular dependence of the high-frequency weak-ferromagnetic mode observed at 142 Gc/s and 273 °K is in satisfactory agreement with theory. The low-temperature antiferromagnetic resonance for H0 along the c axis is similar to previous results; however, off-axis the resonance is observed to greater angles than expected, possibly as a result of a non-zero canting field when the spins deviate from the c axis. Near the Morin transition temperature metamagnetic behaviour is observed and the results are discussed with reference to previous measurements.