Ultrafast spin-transfer switching in spin valve nanopillars with perpendicular anisotropy

In this paper, spin-dependent multiple reflection effect on spin-transfer torque (STT) has been theoretically and numerically studied in a spin valve nanopillar with a single or dual spin-polarizer. By using a scattering matrix method, we formulate an analytical expression of STT that contains the multiple interfacial reflection effect. It is found that the multiple reflections could enhance the STT efficiency and reduce the critical switching current. The STT efficiency depends on the spin polarization of both the free layer and polarizer. In the nanopillars with a dual spin polarizer, the multiple reflections would cause an asymmetric frequency dependence on the applied current, albeit exactly the same parameters are used in all three ferromagnetic layers, indicating that the frequency in the negative current varies much faster than that in the positive case.

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Enhancing Frequency and Reducing the Power of Spin-Torque Nanooscillator By The Generated Oersted Field

SPIN ◽

10.1142/s2010324720500125 ◽

2020 ◽

Vol 10 (02) ◽

pp. 2050012

Author(s):

H. Bhoomeeswaran ◽

P. Sabareesan

Keyword(s):

Spin Valve ◽

Spin Transfer Torque ◽

Spin Transfer ◽

Spin Torque ◽

Spintronic Devices ◽

Frequency Tunability ◽

Spin Polarized ◽

The Individual ◽

Promising Source ◽

Nonmagnetic Spacer

The current-driven magnetization precession dynamics stimulated by Spin-Transfer Torque (STT) in a trilayer spin-valve device (typically Spin-Torque Nanooscillator (STNO)) is numerically investigated by solving the Landau–Lifshitz–Gilbert–Slonczewski (LLGS) equation. We have devised four STNO devices made of ferromagnetic alloys such as CoPt, CoFeB, Fe[Formula: see text]B[Formula: see text]Ni2 and EuO, which act as free and fixed layers. Here, copper acts as a nonmagnetic spacer for all the devices. In this work, we have introduced the current-induced Oersted field, which is generated when a spin-polarized current passes through the device. The generated Oersted field strength is varied by increasing the diameter of the STNO device. Frequency tunability is achieved in all the four devices, whereas the power of the individual device reduces. The frequency and power of the devices depend entirely on the saturation magnetization of the material, which inherently reflects in the current density and the coherence of the spin-polarized DC. In all devices, the frequency increases, whereas the power decreases by increasing the strength of the Oersted field. Among the four devices, the maximum frequency can be tuned up to 104[Formula: see text]GHz with 40[Formula: see text]nm device diameter, which is obtained for EuO material. This opens a promising source and paves a glittering future for the nanoscale spintronic devices.

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Spin transfer torque effects in nanopillar devices with perpendicular anisotropy

10.7567/ssdm.2010.f-9-1 ◽

2010 ◽

Author(s):

S. Mangin

Keyword(s):

Spin Transfer Torque ◽

Spin Transfer ◽

Perpendicular Anisotropy

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Field Dependence of Switching Currents in an Exchange Biased Spin Valve

Journal of Nanoscience and Nanotechnology ◽

10.1166/jnn.2007.18033 ◽

2007 ◽

Vol 7 (1) ◽

pp. 344-349

Author(s):

Hoang Yen Thi Nguyen ◽

Sung-Jung Joo ◽

Kuyoul Jung ◽

Kyung-Ho Shin

Keyword(s):

Magnetic Field ◽

Field Dependence ◽

Spin Valve ◽

Spin Transfer Torque ◽

Information Storage ◽

Spin Transfer ◽

Field Range ◽

Higher Spin ◽

Thermal Magnetization ◽

Negative Field

Current induced magnetic reversal due to spin transfer torque is a promising candidate in advanced information storage technology. It has been intensively studied. This work reports the field-dependence of switching-currents for current induced magnetization switching in a uncoupled nano-sized cobalt-based spin valve of exchange biased type. The dependency is investigated in hysteretic regime at room temperature, in comparison with that of a trilayer simple spin valve. In the simple spin valve, the switching currents behave to the positive and the negative applied magnetic field symmetrically. In the exchange biased type, in contrast, the switching currents respond to the negative field in a quite unusual and different manner than to the positive field. A negative magnetic field then can shift the switching-currents into either negative or positive current range, dependently on whether a parallel or an antiparallel state of the spin valve was produced by that field. This different character of switching currents in the negative field range can be explained by the effect of the exchange bias pinning field on the spin-polarizer (the fixed Co layer) of the exchange biased spin valve. That unidirectional pinning filed could suppress the thermal magnetization fluctuation in the spin-polarizer, leading to a higher spin polarization of the current, and hence a lower switching current density than in the simple spin valve.

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