Weak ferromagnetism in NiCO3

Magnetization curves and neutron diffraction experiments performed at various temperatures on a powdered specimen of NiCO3 point out a Curie temperature TC =24.25 K. Down to 20 K, the spontaneous magnetization follows a (TC −T)1/2 relation. No good agreement exists between the observed and calculated dependencies of the magnetization on T and H on both sides of TC when the calculated values are obtained from an extension correct up to terms in H3 of Dzyaloshinsky’s theory of weak ferromagnetism. On the other hand, the relation m(T,H)= f(H)e−1/2(TC−T) is found to give excellent agreement with the experiments at T