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Commensurate-Incommensurate Magnetic Phase Transition in Magnetoelectric Single Crystal LiNiPO$_4$

D. Vaknin·J. L. Zarestky·J. -P. Rivera·H. Schmid
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Abstract

Neutron scattering studies of single-crystal LiNiPO$_4$ reveal a spontaneous first-order commensurate-incommensurate magnetic phase transition. Short- and long-range incommensurate phases are intermediate between the high temperature paramagnetic and the low temperature antiferromagnetic phases. The modulated structure has a predominant antiferromagnetic component, giving rise to satellite peaks in the vicinity of the fundamental antiferromagnetic Bragg reflection, and a ferromagnetic component giving rise to peaks at small momentum-transfers around the origin at $(0,\pm Q,0)$. The wavelength of the modulated magnetic structure varies continuously with temperature. It is argued that the incommensurate short- and long-range phases are due to spin-dimensionality crossover from a continuous to the discrete Ising state. These observations explain the anomalous first-order transition seen in the magnetoelectric effect of this system.

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D. Vaknin, J. L. Zarestky, J. -P. Rivera, H. Schmid. 2004-01-22. Commensurate-Incommensurate Magnetic Phase Transition in Magnetoelectric Single Crystal LiNiPO$_4$. https://doi.org/10.1103/physrevlett.92.207201

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