Investigation on a giant magnetoelectric effect hexaferrite via neutron scattering techniques with pressure techniques | Shull Wollan Center
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. Pressure often provides alternative modulation on material properties that’s comparable with doping effect. We apply pressure up to 1.8 GPa with CuBe cell and around 4.5 GPa with a Diamond Avail Cell to study the effects of pressure on interactions in this complicated system. Our results suggest that such simultaneously occurred effects can correspond to relatively independent mechanisms.