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Observation and control of domain wall jumps at the nanometer scale

In the present race toward ultra-high density data storage technologies with low energy consumption, many research efforts are focusing on magnetic domain wall based techniques. In a magnetic track, those constitute building blocks that support information, which is read sequentially by moving them using an electrical current. A domain wall corresponds to the transition zone, only a few nanometers thick, between domains with opposite magnetization direction. Their high sensitivity to defects (in the material or from the track edge roughness) limits their mobility and induces an increase of the power needed to move them. In a collaboration, three groups from the Paris-Sud University, coming from Laboratoire Aimé Cotton (LAC), Laboratoire de Physique des Solides (LPS) and Institut d’Electronique Fondamentale (IEF), have developed a new method to observe the pinning of domain walls: a microscope is used to characterize domain walls with nanometric resolution and move them using a local heating induced by a laser. This work, published in Science, shows the high potential of this new imaging technique, in the framework of research on new devices for spintronics.

In this work, domain walls in a ferromagnetic track 1.5 µm wide and only 1 nm thick are studied. A single defect (a nitrogen atom next to a vacancy) included in a nano-diamond attached to an atomic force microscope tip is used as a field sensor. The magnetic field arising from a domain wall is then measured, through the luminescence of the defect. The low tip–to–sample distance and the high sensitivity of the defect gives a high spatial resolution. Furthermore, the laser used for the luminescence measurement induces, at high power, jumps of the domain wall between stable sites (traps), which can then be mapped out. The analysis of the jump frequency allows quantifying the pinning force. Such knowledge is crucial, on the one hand to improve materials for spintronics and on the other part to improve the understanding of domain wall dynamics under the influence of sample defects.


Stanislas Rohart

Nanoscale imaging and control of domain-wall hopping with a nitrogen-vacancy center microscope
J.-P. Tetienne, T. Hingant, J.-V. Kim, L. Herrera Diez, J.-P. Adam, K. Garcia, J.-F. Roch, S. Rohart, A. Thiaville, D. Ravelosona, and V. Jacques
Science 344, 1366-1369 (2014).