Dipartimento di Fisica e Scienze della Terra  
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Manipulating magnetoelectric devices
How to write a magnetic bit with electric fields
Scientists from DiFeST in Parma and the Department of Materials Science in Cambridge have led a study which reports the first observation of a purely electrically driven magnetization reversal which is repeatable and non-volatile. The team also included researchers from Universidad Politecnica de Madrid, Queen Mary University of London and Cranfield University (UK). Non-volatile magnetization reversal is the process though which information is written in magnetic memories, and it is widely believed that the use of electric fields instead of magnetic fields to encode such information could lead to ultra-high density memories with reduced power consumption.

Academic research has strongly contributed to the present hard-disk technology. The first multigigabyte hard disk was commercialised by IBM in 1997, just nine years after the discovery in 1988 of giant magnetoresistance, i.e. the phenomenon which allowed the unprecedented increase in magnetic recording density that made high capacity disks possible. For their independent discovery of giant magneoresistance Albert Fert and Peter Gruenberg were awarded the Nobel prize in 2007. However, continuing demands for ever increasing recording density have now pushed the present technology towards its absolute limits and various innovative approaches to continue the increasing trend are being currently tested. The idea to use electric fields to control magnetism in a magnetic memory looks very attractive because it would potentially cut power consumption, but it requires special materials, so-called "magnetoelectric" materials where electricity and magnetism are coupled. Natural "magnetoelectric" materials are very rare, so an exciting new topic of research is to use artificial magnetoelectric composites, where a ferroelectric and a ferromagnetic material are intimately connected.

In the paper "Non-volatile electrically driven repeatable magnetization reversal with no applied magnetic field (M. Ghidini et al., Nature Communications, 4:1421 doi: 10.1038/ncomms2398 (2013)) the authors show that an electric field can control non-volatile reversals of the local magnetization, in a way that is reminiscent of magnetic memories. The magnetoelectric material they use is an artficial composite, where mechanical deformation produced in the ferroelectric material in response to an electric field is transmitted to a ferromagnetic material whose properties are modified due to the well-known phenomenon of magnetostriction. The researchers also establish a general protocol (shown in the figure) for the electrical control of magnetic information which could inspire the fabrication of prototypes of innovative magnetic memories.

 
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