Linear and quadratic magnetoelectric (ME) effect in Ni-Cl boracite

Abstract

Quasistatic and dynamic measurements of the magnetic field induced magnetoelectric polarization (MEH effect) have been performed in the weakly ferromagnetic/ferroelectric/ferroelastic phase of point group m′m2′ of Ni-Cl boracite between 1.8 and 9 K (=TC) and above. For the first time the quadratic MEH effect of Ni-Cl boracite has been measured and separated from the linear one. The results allow us to discard the existence of a previously assumed antiferromagnetic phase mm2 between 9 and 25 K. Above 9 K, the phase is paramagnetic (mm21′). The coefficients of the linear (α23, α32) and quadratic (β311, β322, β333, and β223) MEH effect are given for 4.2 K. α32 and β322 are also given vs temperature.