Magnetoelectric effect and magnetic torque of chromium chlorine boracite Cr₃B₇O₁₃Cl

Abstract The magnetoelectricity of the boracite Cr3B7O13Cl has been studied by quasistatic and dynamic magnetoelectric (ME) H measurements on (001)cub platelets with a ferroelastic/ferroelectric single domain state, obtained by poling with an electric field of E = 45 kV·cm−1, applied upon cooling through the 42ml′ ⇒ mm21′ phase transition at 160 K. The magnetoelectric effect has been found to be essentially quadratic with typical values of the ME tensor components β333 = 1.5 × 10−18 [s/A] and β322 = 4 × 10−19 [s/A] at 4.2 K, whereas the linear ME coefficient α33 shows strangely small and fluctuating values of the order of 5 × 10−14 [s/m]. The temperature dependence of the ME effect has been measured between 1.8 and 40 K, indicating a spread maximum of β333 near 11 K. The magnetic torque showed a not completely quadratic dependence versus magnetic field at 4.2 K, thus suggesting the contribution of a weakly ferromagnetic ordering. The information obtained at this stage of study permits to derive the magnetic symmetry of Cr3B7O13Cl at 4.2 K only tentatively to be the orthorhombic with point group m'm'2, implying a very weak spontaneous magnetization parallel to the twofold polar axis. The temperature dependence of the spontaneous polarization Ps has been investigated down to 4 K.