Paramagnetoelectric Effects in NiS<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>·6<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>O

Abstract

Piezoelectric paramagnetic crystals can show a linear dependence of the paramagnetic susceptibility on an applied electric field. This effect has been detected in NiS${\mathrm{O}}_{4}$\ifmmode\cdot\else\textperiodcentered\fi{}6${\mathrm{H}}_{2}$O at low temperatures. The thermodynamic inverse effect, the creation of an electric polarization by applied magnetic fields, has also been observed. Both effects are derived from a free energy which for the tetragonal 422 symmetry takes the form $\ensuremath{\xi}({H}_{a}{E}_{b}\ensuremath{-}{H}_{b}{E}_{a}){H}_{c}$, where $c$ denotes the tetragonal axis. The quantity $\ensuremath{\xi}$ has been measured as a function of temperature. It has a pronounced maximum at 3\ifmmode^\circ\else\textdegree\fi{}K, where $\ensuremath{\xi}=2.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ esu. It passes through zero at 1.38\ifmmode^\circ\else\textdegree\fi{}K. Between 10 and 70\ifmmode^\circ\else\textdegree\fi{}K it decreases approximately as ${T}^{\ensuremath{-}2}$. These features are explained by a microscopic theory which considers the linear variation in an applied electric field of all parameters in the spin Hamiltonian of the four ${\mathrm{Ni}}^{++}$ ions in the unit cell. The dominant contribution comes from the change in the crystal-field splitting $D$.

Keywords

Affiliated Institutions

• Harvard University US

Related Publications