Nuclear Antiferromagnetic Double Resonance in MnCO3

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Abstract
The resonance of the low‐frequency branch of MnCO3 shows that the anisotropy field in the (111) plane consists of an approximate temperature‐independent term equal to 0.98±0.04 G and a temperature‐dependent term equal to (8.6±0.3)/Tn. The temperature‐dependent anisotropy field originates from the hyperfine interaction and is proportional to the nuclear polarization which is inversely proportional to the nuclear spin temperature Tn. The nuclei form two sublattices that are coupled antiparallel to the electronic sublattices. This coupling shifts the nuclear frequency from that calculated from its hyperfine field by a factor proportional to the nuclear polarization. At 4.2°K we have observed indirectly the nuclear resonance at 538 Mc/sec by measuring its effect on the electron resonance. It is 102 Mc/sec lower than the frequency we would expect if the nuclear and electron system are decoupled. For intermediate nuclear power levels we have observed two electron resonances at 6 Gc/sec. One of the lines corresponds to the unshifted resonance line the position of the other line was dependent on the nuclear frequency only. This shift is due to partial saturation of the nuclear spin system which saturates at about 640 Mc/sec.