Dual ferroic properties of hexagonal ferrite ceramics BaFe_(12)O_(19) and SrFe_(12)O_(19)

摘要

Dual ferroic properties of a strong magnetism and large ferroelectricity have been observed in barium BaFe_(12)O_(19) and strontium SrFe_(12)O_(19) hexaferrite ceramics. The samples were fabricated by a modified ceramic technique from highly purified raw materials with addition of boron oxide allowing the control of grain size and enhancement of bulk resistivity. Whereas the samples of PbFe_(12)O_(19) fabricated by the same technological method did not have sufficient electric resistivity to support an electric field and did not exhibit the ferroelectric properties. The structure of the samples examined by X-ray diffraction is consistent with a single hexagonal phase. The grains are randomly oriented with the average grain size of 300-400 nm coated with boron oxide. The magnetic properties are characterised by standard ferri-magnetic behavior with the Neel temperature of about 450 ℃ Large spontaneous polarization was observed with the maximal values of 45-50 μC/cm~2 under an applied electric field of 100-300 kV/m. A strong coupling between magnetic and electric ordering was confirmed by measuring the magneto-electric (ME) parameter and magnetodielectric ratio. These ME characteristics are more advanced than those for well-known room temperature multiferroic BiFeO_3. Furthermore, by applying an electric field, the manipulation of magnetization in the range of up to 9% was observed, which is even greater than in some substituted hexaferrites with a non-collinear magnetic structure. The obtained results on electrical polarization are similar to the values reported for the corresponding hexaferrites sintered by polymer precursor technique. This suggests a promising potential of M-type hexaferrite ceramics in devices utilizing magnetoelectric coupling.