Room-temperature magnetoelectric effects in multiferroic Y-type hexaferrites

Y-type hexaferrites are promising single-phase multiferroics where the electric polarization is induced by conical spin orders. The influence of substitution of Sr and Ni on the magnetic and magnetoelectric properties of Y-type hexaferrite BaSrCo₂Fe₁₁AlO₂₂ has been investigated. Sr doping does not change much the Curie temperature T _C near 760 K and the saturation magnetization at 300 K. In contrast, the saturation magnetization is reduced by Ni doping. The spin-induced electric polarization can be reversed by a low magnetic field for all samples, and the doping has almost no influence on the magnetoelectric coefficient at room temperature. The magnetoelectric phase diagrams of all samples have been obtained by the measurements of magnetic field dependence of the dielectric constant at selected temperatures. Both Sr and Ni doping broaden the region of ferroelectric phase by driving the phase boundary to higher magnetic fields. (paper)