Magnetic ratchet for 3-dimensional data storage based on perpendicularly magnetized Pt/CoFeB
The use of (perpendicularly magnetized) synthetic-antiferromagnets (AFM) formed by ferromagnetic (FM) layers coupled anti-ferromagnetically, is highly suitable for a wide field of applications due to the high control achieved in the properties of these artificial structures. Specifically, these synthetic-AFMs have a high potential to be used in spintronic devices [1] . A full understanding of the reversal of such structures under external fields and currents is therefore of high interest. In particular, the perpendicularly magnetized archetypal [[Pt/Co]X/Ru]N with X,N > 1 system has been studied extensively due to its excellent properties for data storage applications and fundamentally for the nano-scale phase-formations it exhibits [2,3].
In this presentation we will discuss our latest study of the tunability of the RKKY-interlayer exchange coupling (IEC) in Pt/CoFeB/Pt/Ru/Pt/CoFeB/Pt stacks with perpendicular magnetic anisotropy (PMA) [4]. By inserting a Pt layer between Ru and CoFeB, the PMA of the ultrathin CoFeB layers is stabilized and the IEC can be tuned. In particular, we show that the IEC versus Pt thickness exhibits a simple exponential decay with a decay length of 0.16 nm.
This allows us to create multilayers (N>>1) using single CoFeB layers with PMA. By carefully tuning the IEC and CoFeB thickness we will show how a sharp magnetic kink soliton can be injected and propagated using a unidirectional ratchet scheme. This paves the way for a novel 3-dimensional shift register, where the data is stored in the 3rd dimension. This potentially holds the promise for a thousand-fold increase in data storage density.
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[2] O. Hellwig, A. Berger, K. J. B., and F. E. E., J. Magn. Magn. Mater. 319, 13 (2007).
[3] O. Hellwig, T. Hauet, T. Thompon, E. Dobisz, J. D. Risner-Jamtgaard, D. Yaney, B. D. Terris, and E. E. Fullerton, Appl. Phys. Lett. 95, 232505 (2009).
[4] R. Lavrijsen, A. Fernández-Pacheco, D. Petit, R. Mansell, J. H. Lee, and R. P. Cowburn, Appl. Phys. Lett., 100, 052411, (2012)