On June,8, Michael Foerster from Alba Synchrotron, will visit Spintec. At 11H, he will give a talk on “Magnetism catches the wave: Direct imaging of delayed magneto dynamic modes induced by strain waves”.

Magnetism catches the wave: Direct imaging of delayed magneto dynamic modes induced by strain waves

Surface Acoustic Waves (SAWs) are propagating Raleigh waves in the upper micrometric layer of a crystal, which propagate large distances and can be generated in piezoelectric materials by applying RF electric fields to transducer electrodes on the surface. We have shown that it is possible to image such waves in LiNbO3 by stroboscopic X-ray PhotoEmission Electron Microscopy (XPEEM), since it is sensitive to the piezoelectric part of the SAW. The dynamic strain associated to the SAW allows the study of fast strain induced processes in structures grown onto the LiNbO3 with temporal resolution below 100 ps and down to 50 nm spatial resolution. The stroboscopic imaging can be also used to separate and tune propagating and standing components of the SAW. Standing SAW could be used to create tunable periodic patterns of strain dependent properties on the sample.
We use propagating SAW to study the magneto-elastic effect or inverse magnetostriction, which has attracted much interest as relevant coupling mechanism in multiferroic heterostructures. Using XMCD contrast, the magnetic state of the Ni microstructures in the acoustic path is imaged (XMCD-PEEM) while simultaneously resolving the SAW phase, i.e. the strain state of the Ni. We found that the magnetoelastic effect on the subnanosecond timescale is still comparably efficient as for the static strain case. Most strikingly, different delays in the order of 100 – 300 ps of the magnetic response with respect to the strain wave are measured. These delays are dependent and directly related with the intrinsic magnetization dynamics of the Ni patterns [1]. Thus it is shown that the magnetoelastic effect itself is not limiting the speed of a potential device on this scale, but that the magnetization state has to be properly chosen.

[1] M. Foerster et al., arXiv:1611.02847