High-Frequency Resonance of A Weak Ferromagnet: MnCO3

The high-frequency resonance of MnC${\mathrm{O}}_3$ in the canted state was found at 95.7 Gc/sec in zero field at 20.4°K which corresponds to a uniaxial anisotropy energy of 31.4×${10}^{-3\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$. The frequency dependence of the resonance for magnetic fields parallel to the [111] direction and the angular dependence of the resonance for constant frequency were measured. The latter was found to be different from that of a pure antiferromagnet due to the anisotropic spin-spin interaction. At absolute zero we estimated the zero-field splitting to occur at approximately 132 Gc/sec. When the magnetic field was applied in the (111) plane, the resonance could not be observed due to broadening effects. The broadening effects were also large in magnetic fields smaller than 7 kG. MnC${\mathrm{O}}_3$ is the first weak ferromagnet with anisotropic spin-spin interaction where the high-frequency branch has been found.