Characterization of Y-type hexaferrite Ba2Mg2Fe12O22 powders

Ba2Mg2Fe12O22 is a Y-type hexagonal ferrite known for a relatively high temperature (similar to 200 K) of the magnetic transition to a spiral spin arrangement and an easy magnetization axis lying in a plane perpendicular to the c crystal axis. The multiferroicity exists in the absence of an external magnetic field H; a longitudinal-conical spin arrangement sets below 50 K; and the direction of the electric polarization Pcan be governed by relatively low magnetic fields (<0.02 T). The structural, magnetic and ferroelectric parameters have been mostly studied on monocrystals and, in spite of the attractive possibilities of designing promising composite multiferroic structures, the information on Ba2Mg2Fe12O22 powders is scarce. We report on Ba2Mg2Fe12O22 powders studied by X-ray and neutron powder diffraction, and magnetometry. The samples were prepared by two different techniques: sonochemical co-precipitation and sol-gel auto-combustion. The structures retained the rhombohedral crystal symmetry, but mixed occupancies of the 14 (Mg, Fe) cation sites was a new feature. The magnetizations at a magnetic field of 60 kOe at 300 K were 22.78 emu/g for the sample prepared by sol-gel auto-combustion, and 24.95 and 25.06 emu/g for the samples obtained by sonochemical co-precipitation and annealed at 1170 degrees C and 1200 degrees C, respectively.