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Features of magnetization reversal in a MRAM cell — II. Perpendicular anisotropy  

 Ostrovskaya N.V.
 Skidanov V.A.
 Skvortsov M.S.
Date of publication

 The magnetic random access memory (MRAM) at-tracts the attention of electronics engineers due to its high speed of magnetic switching, low energy consump-tion, high data storage density and reliability. In the basic publication by J. Slonczewski (1996), the first suggested model had composed of two ferromagnetic layers with in-plane anisotropy separated by nonmag-netic interlayer. However, both calculations and exper-iments showed that switching currents in the classical ferromagnets, such as cobalt and iron, are too high. Search for ways to reduce the current was in a direction to optimize the design, and the direction of search for the best materials. It was found experimentally that the most optimal materials for magnetic tunneling junctions were the ferromagnetic alloys FeCoB with nonmagnetic interlayer MgO, and the most promising design solution was a memory cell with perpendicular magnetic anisotropy.
In our work we investigated theoretically the features of switching dynamics in such a model. For this pur-pose, the system of ordinary differential equations in approximation of uniform magnetization distribution for magnetization dynamics in the valve with perpendicular anisotropy was derived. It was shown that in such a system, in contrast with the system for the in-plane anisotropy, there are only two equilibrium positions of the magnetization vector, namely, . The stability analysis of the stationary points of the system allowed us to obtain the analytical expressions for the threshold values of switching magnetic fields and currents and to construct the bifurcation diagram of the magnetization dynamics. With its help, the classification of types of dynamics versus field and current values was performed. The re-gions of limit cycles existence and the regions of optimal magnetization switching were revealed. The results were compared with those for the cell with in-plane anisotropy. It was found that the switching current for the cell with perpendicular anisotropy is an order lower that this one for the cell with in-plane anisotropy.
 MRAM, perpendicular anisotropy, magnetization, free layer, fixed layer, the Landau–Lifshits–Gilbert equation, magnetization reversal
Library reference
 Ostrovskaya N.V., Skidanov V.A., Skvortsov M.S. Features of magnetization reversal in a MRAM cell — II. Perpendicular anisotropy // Problems of Perspective Micro- and Nanoelectronic Systems Development - 2016. Proceedings / edited by A. Stempkovsky, Moscow, IPPM RAS, 2016. Part 4. P. 230-236.
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