Crystal growth of hexaferrite architecture for magnetoelectrically tunable microwave semiconductor integrated devices

• Online Access: http://hdl.handle.net/2047/D20193853

Hexaferrites (i.e., hexagonal ferrites), discovered in 1950s, exist as any one of six crystallographic structural variants (i.e., M-, X-, Y-, W-, U-, and Z-type). Over the past six decades, the hexaferrites have received much attention owing to their important properties that lend use as permanent magnets, magnetic data storage materials, as well as components in electrical devices, particularly those operating at RF frequencies. Moreover, there has been increasing interest in hexaferrites for new fundamental and emerging applications. Among those, electronic components for mobile and wireless communications especially incorporated with semiconductor integrated circuits at microwave frequencies, electromagnetic wave absorbers for electromagnetic compatibility, random-access memory (RAM) and low observable technology, and as composite materials having low dimensions. However, of particular interest is the magnetoelectric (ME) effect discovered recently in the hexaferrites such as SrScxFe_12-xO₁₉ (SrScM), Ba_2[nil]xSr_xZn₂Fe₁₂O₂₂ (Zn₂Y), Sr₄Co₂Fe₃₆O₆₀ (Co₂U) and Sr₃Co₂Fe₂₄O₄₁ (Co₂Z), demonstrating ferroelectricity induced by the complex internal alignment of magnetic moments. Further, both Co₂Z and Co₂U have revealed observable magnetoelectric effects at room temperature, representing a step toward practical applications using the ME effect. These materials hold great potential for applications, since strong magnetoelectric coupling allows switching of the FE polarization with a magnetic field (H) and vice versa. These features could lead to a new type of storage devices, such as an electric field-controlled magnetic memory.