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Stability phase diagram of perpendicular magnetic tunnel junction in non-collinear geometryтезисы доклада
- Авторы: Strelkov N., Timopheev A., Sousa R., Chshiev M., Buda-Prejbeanu L.D., Dieny B.
- Сборник: INTERMAG Europe 2017 Digest Book
- Серия: INTERMAG
- Тезисы
- Год издания: 2017
- Издательство: Institute of Electrical and Electronics Engineers
- Местоположение издательства: Piscataway, NJ, United States
- Первая страница: 1807
- Последняя страница: 1807
- Аннотация: Magnetic tunnel junctions (MTJ) based on perpendicular magnetic anisot- ropy systems are intensively studied for the development of the next genera- tions of spin transfer torque magnetic random access memories. The stability field-voltage diagrams (VH diagrams) are useful tools to study the mech- anisms and the properties of STT induced magnetization reversal in such devices. However, these diagrams are usually measured in a collinear geom- etry, i.e. with the external magnetic field applied parallel to the easy-axis of MTJ magnetic layers (free layer and polarizer) [1,2]. Considering the rising interest for non-collinear geometries, it is also interesting to study these phase diagrams once the field is applied at some angle with respect to the normal to the layers, introducing thus a non-collinearity in the static configuration of the storage and polarizer layers. Non-collinear configura- tion of magnetic electrodes influences the switching characteristics of the storage layer and its field dependence defines the phase boundaries of the stability diagram. In this study systematic experimental measurements were performed on MgO-based magnetic tunnel junctions with various diameters ranging from 50 nm to 150 nm. We found that the shape of the stability field- voltage diagrams depends strongly on the direction of the applied field while the bistable parallel (P) / antiparallel (AP) region preserves its symmetry around the origin (Fig.1a). We have found also a quite noticeable differ- ence in the shape of measured and simulated hard-axis VH diagrams, H in the hard plane, when considering that the anisotropy is only of uniaxial form. However, a good agreement between experiments and simulations is recovered when a second order anisotropy contribution is introduced in the model [3,4,5]. The signature of this higher order anisotropy term is not always visible in the collinear geometry but clearly shows up once the field is applied away from the normal to plane of the sample (Fig.1b). Further- more, performing the stability analysis in linear approximation allowed us to analytically extract the critical switching voltage at zero temperature for in-plane field. This study indicates that in the non-collinear geometry inves- tigations are suitable to detect the presence of second order term in the anisotropy. Such higher order anisotropy term can yield an easy-cone anisot- ropy which reduces the thermal stability factor but allows for faster and more reproducible spin transfer torque switching due to a reduced stochasticity of the switching onset. As a result, the energy per write event decreases much faster than the thermal stability factor as the second order anisotropy becomes more negative. For memory applications the second order anisot- ropy appears to be an interesting parameter to control and adjust, since it allows to write with lower energy and less stochastically while preserving a reasonable thermal stability. [1] A. A. Timopheev, R. Sousa, M. Chshiev, L. D. Buda-Prejbeanu and B. Dieny, Phys. Rev. B 92, 104430 (2015). [2] L. Cuchet, B. Rodmacq, S. Auffret, R. C. Sousa, I. L. Prejbeanu and B. Dieny, Scientific Reports 6, 21246 (2016). [3] A. A. Timopheev, R. Sousa, M. Chshiev, H. T. Nguyen and B. Dieny, Scientific Reports 6, 26877 (2016). [4] J. M. Shaw, H. T. Nembach, M. Weiler, T. J. Silva, M. Schoen, J. Z. Sun and D. C. Worledge, IEEE Magn. Lett. 6, 1 (2015). [5] J. Z. Sun, Phys. Rev. B 91, 174429 (2015).
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