Magnetoelectric Hexaferrites

Magnetoelectric (ME) multiferroics are materials that combine coupled electric and magnetic dipoles. Studies of ME multiferroics are a time-honored research subject because of their potential for future electronic devices. Recent discoveries have revealed that ferroelectricity can be induced by complex internal arrangements of magnetic moments. This new family of multiferroics is called magnetically induced ferroelectrics. Magnetically induced ferroelectrics are known to show giant ME effects, i.e., changes in ferroelectric polarization upon application of an external magnetic field. However, their ME effects usually occur at temperatures that are too low and at applied external fields (> similar to 0.1 T) that are too high to be of practical use. Thus, the quest for a robust room-temperature ME effect is a major challenge in ME research. Lately, some ferrites with hexagonal crystal structures, termed hexaferrites, have been found to show ME effects at room temperature and low magnetic fields (similar to 0.01 T). The results represented an important step toward practical applications using the ME effect in magnetically induced ferroelectrics. This review introduces structure, magnetism, and resulting magnetoelectricity of hexaferrite systems, which are promising candidate materials for ME devices.