22 - Single-phase, composite and laminate multiferroics

Abstract

Magnetoelectric (ME) effect has been envisaged as a promising route to develop new electronic technologies such as uncooled magnetic field sensors, nonvolatile memories, and ferroelectric photovoltaics, just to name a few. An intrinsic ME behavior can occur in a single-phase compound. Unfortunately, to date no single-phase magnetoelectric multiferroic (MM) material was discovered that meets the room-temperature ME requirements for memory applications. The most severe weaknesses of single-phase MMs are linked to their operational temperatures (most only operate well below room temperature), but also to the magnitudes of the order parameters. In the film form, their switchable polarization is extremely low, usually in the order of magnitude of nC/cm2. Basically, such values are one order of magnitude lower than the desirable minimum of ~1μC/cm2 required by a computer memory sense amplifier to discriminate between 1 and 0 states. Multiferroics (MFs) that exhibit reasonably high operating temperatures tend to be weak ferromagnets or antiferromagnets, however strong ferromagnets are desirable, for the ease of READ/WRITE operations. Finally, the magnetic fields currently required to switch the polarization of single-phase MFs are orders of magnitude larger than the mT required for a magnetic random access memory. Hence, the deployment of a multiferroic RAM is not envisaged in the near future; however, there are other equally important devices with less stringent requirements that may be developed.