New physics revealed by images taken by the first PMOKE microscope in Argentina🇦🇷
Updated: Feb 12
Since 2016 the first Polar Magneto-Optic Kerr effect microscope in Argentina is operative at the Bariloche Atomic Center. This technology allows capturing optical images of ferromagnetic systems with micrometric resolution. Moreover, it allows the study of the dynamics of ferromagnetic interfaces under the effects of magnetic fields at velocities that expand over 10 orders of magnitude. Applications of these studies are, for example, the development and improvememt of magnetic memories (generally used in satellites).
The first images captured with this microscope were taken by Iván Fernández Aguirre and Lucas J. Albornoz, at that time master students of Balseiro Institute under the supervision of Prof. Javier Curiale and Dr. Sebatian Bustingorry. They probed the dynamics of ferromagnetic interfaces in the so-called creep regime in [Co/Ni] based multilayers grown in Thales, France.
In the creep regime, a highly non-linear velocity response is expected as a consequence of the interplay of the effects of disorder, temperature, and the interface elasticity. We observed this regime in [Co/Ni] samples at very low fields. Approaching the depinning field from below results in an unexpected excess velocity with respect to the creep law.
We analyze these results using scaling theory to show that this speeding up of domain wall motion can be interpreted as due to the increase of the size of the deterministic relaxation close to the depinning transition. We propose a phenomenological model to accurately fit the observed excess velocity and to obtain characteristic values for the depinning field, the depinning temperature, and the characteristic velocity scale for each sample.
This exess velocity was reported by other authors in many other ferromagnetic samples, but never explained. Our theory provides a method to explain this phenomenon and on the practical side, it allows to obtain sample characteristic values when deviations from the creep regime are observed.
These results were published in:
Nirvana Caballero, I. Fernández Aguirre, L. J. Albornoz, A. B. Kolton, J. C. Rojas-Sánchez,
S. Collin, J. M. George, R. Diaz Pardo, V. Jeudy, S. Bustingorry, and J. Curiale. Excess velocity of magnetic domain walls close to the depinning field Phys. Rev. B 96, 224422, 2017.