Evidence for the magnetoelectric effect in nickel-bromine boracite, Ni3B7O13Br

Abstract
A ferromagnetic/ferroelec./ferroelastic phase, consistent with Point Group m'm2' and TC(f.m.) = 17 K, was identified by measurements of the magnetoelec. coeff. α32, peak value at TC (7 ps/m), and the ferromagnetic coercive field, Hc, vs. temp. A magnetoelec. effect persists above 17 K up to ∼30 K, indicating a phase of still unknown nature. The dielec. const. ε33 is insensitive to magnetic ordering, but a striking anomaly of spontaneous polarization, Ps, occurs in the magnetic ordering range and is attributed to a spontaneous magnetoelec. interaction. Further, Ps is (290 nC/cm2) at TC(f.e.)