Critical Field of Spin Torque Oscillator with Perpendicularly Magnetized Free Layer

Taniguchi, Tomohiro; Arai, Hiroko; Tsunegi, Sumito; Tamaru, Shingo; Imamura, Hiroshi

doi:10.7567/apex.6.123003

Cited by 62 publications

(106 citation statements)

References 31 publications

Supporting

Mentioning

101

Contrasting

Order By: Relevance

“…5(b), where the spin torque cancels the damping torque. The balance current, or the LLG equation averaged over a constant energy curve, has been used to derive theoretical conditions of spin torque switching, spin-torqueinduced self-oscillation, thermally activated magnetization switching, and microwave-assisted magnetization reversal [37,38,63,[65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82].…”

Section: Balance Currentmentioning

confidence: 99%

Magnetization switching by current and microwaves

2016

Self Cite

View full text Add to dashboard Cite

We propose a theoretical model of magnetization switching in a ferromagnetic multilayer by both electric current and microwaves. The electric current gives a spin transfer torque on the magnetization, while the microwaves induce a precession of the magnetization around the initial state. Based on numerical simulation of the Landau-Lifshitz-Gilbert (LLG) equation, it is found that the switching current is significantly reduced compared with the switching caused solely by the spin transfer torque when the microwave frequency is in a certain range. We develop a theory of switching from the LLG equation averaged over a constant energy curve. It was found that the switching current should be classified into four regions, depending on the values of the microwave frequency. Based on the analysis, we derive an analytical formula of the optimized frequency minimizing the switching current, which is smaller than the ferromagnetic resonance frequency. We also derive an analytical formula of the minimized switching current. Both the optimized frequency and the minimized switching current decrease with increasing the amplitude of the microwave field. The results will be useful to achieve high thermal stability and low switching current in spin torque systems simultaneously.

show abstract

Section: Balance Currentmentioning

confidence: 99%

Magnetization switching by current and microwaves

2016

Self Cite

View full text Add to dashboard Cite

show abstract

“…Because the pinned layer is taken to be in the film plane, an asymmetric angle dependence of the spin torque is essential for dynamics to be induced within the single-domain model. The coefficient P(I) is defined as [31][32][33] …”

Section: Model Descriptionmentioning

confidence: 99%

Oscillation characteristics of zero-field spin transfer oscillators with field-like torque

2015

View full text Add to dashboard Cite

Spin torque oscillator frequency versus magnetic field angle: The prospect of operation beyond 65 GHz Applied Physics Letters 94, 102507 (2009) We theoretically investigate the influence of the field-like spin torque term on the oscillation characteristics of spin transfer oscillators, which are based on MgO magnetic tunnel junctions (MTJs) consisting of a perpendicular magnetized free layer and an in-plane magnetized pinned layer. It is demonstrated that the field-like torque has a strong impact on the steady-state precession current region and the oscillation frequency. In particular, the steady-state precession can occur at zero applied magnetic field when the ratio between the field-like torque and the spin transfer torque takes up a negative value. In addition, the dependence of the oscillation properties on the junction sizes has also been analyzed. The results indicate that this compact structure of spin transfer oscillator without the applied magnetic field is practicable under certain conditions, and it may be a promising configuration for the new generation of on-chip oscillators. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

show abstract

“…The oscillation properties of this type of spin-torque oscillator, such as the relation between the injected current and the oscillation frequency, as a single oscillator have been investigated both experimentally [22] and theoretically [23]. A possibility to excite a mutual synchronization in this type of spin-torque oscillators, however, has not been investigated yet.…”

mentioning

confidence: 99%

Mutual synchronization of spin-torque oscillators consisting of perpendicularly magnetized free layers and in-plane magnetized pinned layers

Taniguchi

Tsunegi

2017

Appl. Phys. Express

Self Cite

View full text Add to dashboard Cite

A mutual synchronization of spin-torque oscillators coupled through current injection is studied theoretically. Models of electrical coupling in parallel and series circuits are proposed. Solving the Landau-Lifshitz-Gilbert equation, excitation of in-phase or antiphase synchronization, depending on the ways the oscillators are connected, is found. It is also found from both analytical and numerical calculations that the current-frequency relations for both parallel and series circuits are the same as that for a single spin-torque oscillator.Spin-torque oscillators have been a fascinating research target in the field of spintronics from the viewpoints of both nonlinear science and practical applications such as microwave generator and communication devices [1][2][3][4][5][6]. Above all, the exciting topic in this research field is the synchronization of spin-torque oscillators by the magnetic [7][8][9][10] and/or electrical [11][12][13][14][15] couplings. The synchronization of spin-torque oscillators results in an enhancement of the emission power and an increase of the quality factor of the practical devices. In addition, new applications such as brain-inspired computing based on the synchronized spin-torque oscillators are proposed very recently [16][17][18][19].An attractive structure of spin-torque oscillator for practical applications is that consisting of a perpendicularly magnetized free layer and an in-plane magnetized pinned layer [20][21][22] because this type of spin-torque oscillator results in high emission power, narrow linewidth, and wide frequency tunability simultaneously. The oscillation properties of this type of spin-torque oscillator, such as the relation between the injected current and the oscillation frequency, as a single oscillator have been investigated both experimentally [22] and theoretically [23]. A possibility to excite a mutual synchronization in this type of spin-torque oscillators, however, has not been investigated yet.In this letter, a theoretical study on the mutual synchronization of spin-torque oscillators consisting of perpendicularly magnetized free layers and in-plane magnetized pinned layers is presented. We focus on the coupling of spin-torque oscillators through the current injection, and develop models of the coupling in the parallel and series circuits. Solving the Landau-Lifshitz-Gilbert (LLG) equation numerically, we show that two spin-torque oscillators indicate in-phase or antiphase synchronization depending on the way the oscillators are connected. An analytical theory clarifying the relation between the current, oscillation frequency, and phase difference is also developed. Both the numerical and analytical calculations indicate that the dependence of oscillation frequency on the current for both the parallel and series circuits are identical to that of a single spin-torque oscillator.The system under consideration is schematically shown in Fig. 1. There are two spin-torque oscillators, and each oscillator consists of a free layer F k (k = 1, 2) and a pinned ...

show abstract

Critical Field of Spin Torque Oscillator with Perpendicularly Magnetized Free Layer

Cited by 62 publications

References 31 publications

Magnetization switching by current and microwaves

Magnetization switching by current and microwaves

Oscillation characteristics of zero-field spin transfer oscillators with field-like torque

Mutual synchronization of spin-torque oscillators consisting of perpendicularly magnetized free layers and in-plane magnetized pinned layers

Contact Info

Product

Resources

About