MAGNETISM OF SYNTHETIC AND NATURAL MNCO3

Weakly ferromagnetic MnCO3 powder with TN=32.2°K shows single-domain behavior with coercive force of about 3.5 kOe at 4.2°K. The differential susceptibility at dc and 10 MHz is less at low fields than at high fields for T<10°K; the remanent susceptibility is the same as the initial susceptibility. The measurements are consistent with a magnetization process involving spin flopping of the sublattices in the low-anisotropy basal plane. The measured remanent moment at 4.2°K indicates a spontaneous (ferromagnetic moment of 92 emu/mole in pure MnCO3. Natural crystals of composition Mn0.95Fe0.05CO3 (2.3% Fe by weight) show no weak ferromagnetism below TN=35°K. Instead, the spins are aligned parallel to the trigonal crystal axis, resulting in normal uniaxial antiferromagnetism. The large anisotropy of the Fe++ impurities is assumed to be the cause. © 1969 The American Physical Society.