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
Some solid materials develop electrical charge in response to an applied mechanical stress. This piezoelectric effect means that certain crystals can be used to convert mechanical energy into electricity or vice-versa, and piezoelectric materials are used in a variety of technologies, including the automatic focusing of cameras in mobile phones. For these applications, the strain varies continuously with applied voltage, but cycling the applied voltage can lead to discontinuous changes of strain due to ferroelectric domain switching. These discontinuous changes in strain can be used to drive magnetic switching in a thin ferromagment film, such that data can be written electrically, and stored magnetically.
For Professor Neil Mathur at the University of Cambridge, taking a closer look seemed obvious.
The data allowed us to do a pixel-by-pixel comparison of the images, and I felt that we should do that, simply because we could.
Unexpectedly, the pixel‑by‑pixel comparison revealed that the magnetic switching angles typically fell well short of 90°. This could be easily explained by including a shear component, predicted from the PMN-PT unit‑cell geometry.
This new finding should be applicable to similar materials, and offers both a challenge and an opportunity for the development and miniaturisation of devices based on magnetoelectric materials.
Professor Mathur explains:
Our finding means that these systems are going to behave differently to what one would have originally expected after miniaturisation. This will be a challenge for device designers, but there is also a huge opportunity here, because it means that two sets of data can be written to the same device with magnetic and electric fields, thus doubling the storage density.
In future, Professor Mathur believes it will become normal to consider the shear strain that arises when low‑symmetry ferroelectric domains undergo switching.
Ghidini M et al. Shear-strain-mediated magnetoelectric effects revealed by imaging. Nature Materials (2019). DOI: 10.1038/s41563-019-0374-8.
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