Spontaneous magnetostriction in the ordered phase of NiCI2

Spontaneous magnetostriction is measured for the first time in the ordered phase of NiCl2 by using two independent methods (powder x-ray diffractometry and dilatometry in crossed magnetic fields). These methods differ in that the change in the lattice parameters upon a transition to the ordered polydomain state, which is effectively isotropic in the basal plane, is measured in the former case, while the change in the sample size as a result of monodomainization of the state induced by the magnetic field is measured in the latter case. In spite of a qualitative similarity (positive striction in the hexagonal plane of magnetic ordering and compression along the c-axis), the results exhibit considerable quantitative differences. The spontaneous striction determined by using the x-ray technique is uxx = uyy = (7.2±2.2) · 10−4 in the plane and uzz = − (8.7±3.3) · 10−4 along the c-axis, which is approximately an order of magnitude larger than dilatometric value (besides, dilatometrically measured striction turns out to be strongly anisotropic in the basal plane, which is quite natural).

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