Synthesis and multiferroic properties of M-type SrFe12O19 hexaferrite ceramics

• SrFe12O19-hexaferrites show strong room-temperature multiferroic properties.
• Modified ceramic technique helps to increase resistivity of hexaferrites.
• Large spontaneous polarisation is observed in single-phase SrFe12O19.
• External electric field deceases the remanent magnetisation of SrFe12O19 by 10%.

The coexistence of strong ferromagnetism and large ferroelectricity has been observed in pure strontium hexaferrite SrFe12O19 fabricated by a modified ceramic technological method from highly purified initial materials with addition of boron oxide in mass concentration of less than 1.5%. The structure of the samples confirmed by X-ray diffraction patterns is consistent with a single hexagonal phase. The samples were polycrystalline with the grain size of 300–400 nm and the intergrain space was field with B2O3. The use of boron oxide resulted in enhanced resistivity enabling proper electric polarisation measurements. The magnetic properties are characterised by a standard ferrimagnetic behaviour with the Neel temperature of about 450 °C. Large electric polarisation was observed with the remnant value of 22 μC/cm2 and the maximal value of 45 μC/cm2 under the electric field of 300 kV/m. A strong coupling between magnetic and electric ordering was confirmed by measuring the magnetoelectric parameter and the electric field-controlled magnetic hysteresis. The change in magnetization by applying an electric field was in the range of 9–10%, which is even greater than that observed in some substituted hexaferrites with a magnetically induced electric polarisation. The combination of room-temperature multiferroic properties and electrically tuneable magnetization is promising for applications in magnetoelectric devices.