IMF2017

Y-type hexaferrite Ba₂Mg₂Fe₁₂O₂₂ was reported recently to have a large magnetoelectric effect (ME). The magnetic structure of Ba₂Mg₂Fe₁₂O₂₂ consists of two groups of L- (large moment) and S- (small moment) blocks alternating stacked along the c-axis direction. The moments align ferrimagnetically in the same block. At zero field, it displays a proper screw magnetic structure with an incommensurate wavevector k along the c-axis below a ferrimagnetic-antiferromagnetic (FM-AFM) transition (195 K) and then transforms to a longitudinal conical phase below 50 K. Applying a small magnetic field, the material displays polarization in the conical phase. When doped with Sr, the material keeps its sensitivity to field while the ME coefficient is greatly enhanced with Sr doping. The transition temperatures are largely elevated and FM-AFM transition temperature goes above room temperature. Meanwhile, temperature dependent neutron diffraction investigation shows pinning effect emerging at heavy Sr doped sample that has an alternating longitudinal conical ground state. The study of size effect indicate that such simultaneously occurred effects can correspond to relatively independent mechanisms. Comparison study of the crystal and magnetic structure of the doped samples is performed to identify the moment interaction picture differences behind doping effects.