Multiferroism in strained strontium hexaferrite epitaxial thin films

Ferrimagnetic SrFe12O19 (SrM) is a mother phase for ferrite permanent magnets, which are commonly used due to its low cost compared to that of Nd-based permanent magnets and broader uses in permanent magnet markets. Recently, its electronic ground state has been debated. It has been proposed that the SrM is in a quantum paraelectric state in its single-crystal form, while polycrystalline SrM is a ferroelectric state. In this work, strain can stabilize ferroelectricity at room temperature, while keeping its ferrimagnetism. The strained SrM shows not only clear magnetic hysteresis but also ∼4.4μC/cm2 as remnant polarization. From high-temperature thermal annealing, its crystallinity and ferroelectricity are even strengthened. Those are visualized by significant reduction in full width at half maximum of the rocking curve and ∼7.9μC/cm2 in remnant polarization The results indicate this functionality can be discovered from old and well-known materials.