Spin torque oscillator with perpendicularly magnetized free layer and in-plane magnetized pinned layer
Vendredi 11 juillet 2014 14:00
- Duree : 1 heure
Lieu : Salle de Séminaire de SPINTEC, Bât 1005 au 2ème étage, CEA Grenoble, 17 rue des martyrs
Orateur : Tomohiro TANIGUCHI (AIST, Tsukuba, Japan)
Direct current applied to a magnetic tunnel junction exerts spin torque on the magnetization of the free layer. When the energy supplied by the spin torque balances the energy dissipation due to the damping, self-oscillation of the magnetization can be excited. Spin torque oscillator (STO) utilizing this self-oscillation is an important spintronics device applicable to nano-communication devices due to its small size, high emission power, and frequency tunability. Recent development of the experimental technique to enhance the perpendicular magnetic anisotropy of CoFeB by adding an MgO capping layer enabled us to fabricate STO consisting of a perpendicularly magnetized free layer and an in-plane magnetized pinned layer. It was experimentally shown that this type of STO in could show a large emission power ( 0.5 micro Watt) with a narrow linewidth ( 50 MHz) [1]. Therefore, this type of STO will be the model structure for practical STO applications.
In this study, we report recent development of the theory of the magnetization dynamics in STO. Based on the energy balance equation between the spin torque and damping, we have revealed relations between the current, applied magnetic field, magnetic anisotropy, oscillation frequency, linewidth, and so on. For example, we predicted the existence of a critical field magnitude below which the controllable range of the oscillation frequency by the current is suppressed [2]. This prediction was experimentally confirmed very recently [3]. We also showed that the quality factor of STO, which is defined by the ratio between the oscillation frequency and linewidth, can be larger than 104 by applying a large current (typically, 10 mA), which is two orders of magnitude larger than the experimentally observed value [4]. The latest result is a prediction of the self-oscillation at zero-field assisted by field-like torque [5]. We will talk the details of these results, as well as the latest experimental results.
[1] H. Kubota et al., Appl. Phys. Express 6, 103003 (2013).
[2] T. Taniguchi et al., Appl. Phys. Express 6, 123003 (2013).
[3] S. Tsunegi et al., Jpn. J. Appl. Phys. 53, 060307 (2014).
[4] T. Taniguchi, Appl. Phys. Express 7, 053004 (2014).
[5] T. Taniguchi et al., Appl. Phys. Lett. 104, 152411 (2014).
Contact : ursula.ebels@cea.fr
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