Feeling the strain: shear effects in magnetoelectric switching

Diamond uncovers unexpected complexity that may aid magnetoelectric data storage devices.

The high resolution and wealth of data provided by an experiment at Diamond can lead to unexpected discoveries. The piezoelectric properties of the ceramic perovskite PMN-PT (0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3) are widely used in commercial actuators, where the strain that is generated varies continuously with applied voltage. However, if the applied voltage is cycled appropriately then there are discontinuous changes of strain. These discontinuous changes can be used to drive magnetic switching in a thin overlying ferromagnet, permitting magnetic information to be written electrically. An international team of researchers used beamline I06 to investigate a ferromagnetic film of nickel when it served as a sensitive strain gauge for single-crystal PMN-PT. Their initial interpretation of the results suggested that ferroelectric domain switching rotated the magnetic domains in the film by the expected angle of 90°, but a closer examination revealed the true picture to be more complex. Their work, recently published in Nature Materials, shows that the ferroelectric domain switching rotated the magnetic domains in the film by considerably less than 90° due to an accompanying shear strain. The findings offer both a challenge and an opportunity for the design of next-generation data storage devices, and will surely be relevant if the work is extended to explore the electrically driven manipulation of more complex magnetic textures.

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Image: Magnetic vector map (50 µm field of view) describing the magnetisation of a Ni film while applying 50 V across the ferroelectric substrate of PMN-PT. The colour wheel identifies magnetisation direction. Yellow and brown denotes regions whose magnetisation was unaffected by the voltage.