Dynamics of the magnetization reversal in Au/Co/Au micrometer-size dot arrays

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Jamet, J. | Lemerle, S. | Meyer, P. | Ferré, J. | Bartenlian, B. | Bardou, N. | Chappert, C. | Veillet, P.

Edité par CCSD ; American Physical Society -

International audience. In high-quality Au/Co/Au ultrathin films with high perpendicular magnetic anisotropy, magnetization reversal occurs through easy domain-wall (DW) propagation following rare nucleation events, located at major structural defects. By patterning arrays of dots in such films, we block the DW propagation, and thus sample the intrinsic distribution of nucleation sites, improving precision as the dot diameter decreases. In a Au/Co (1 nm)/Au film we have fabricated large area arrays of round dots, with diameters of 1 and 2 μm, leaving aside an unpatterned area as a witness of the magnetization reversal in a “continuous film” having undergone all patterning steps. Polar magneto-optical (MO) Kerr effect was used in both global and imaging experiments to accurately measure the hysteresis loops and aftereffect phenomena. We show that, despite limited damage induced by patterning, the expected behavior is indeed observed. A statistical model was developed, assuming an intrinsic distribution of nucleation sites in the initially continuous film, a uniform nucleation volume (Formula presented) and a linear dependence of the nucleation energy barrier (Formula presented) on both applied field (Formula presented) and nucleation field (Formula presented) at a given site ((Formula presented) is the saturation magnetization). Comparison between experiments and theory shows an excellent overall agreement, and allows one to obtain an approximate view of the distribution of nucleation fields. We could extract two fundamental lengths, the nucleation length (Formula presented) (related to (Formula presented)), and the mean distance (Formula presented) between nucleation sites. (Formula presented) was found to be equal to (Formula presented) in good agreement with previous determinations on similar films. (Formula presented) equal to about 430 nm, could be viewed as a measure of the typical distance between major structural defects in the “continuous film.” Our method is indeed a means to characterize nanometer scale magnetic events (reversal of a nucleation volume), using micrometer scale resolution experiments (MO imaging). This is an example of how microfabrication can help us to understand magnetization reversal in a continuous ultrathin film.

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