Switching Behaviors and its Dynamics of a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Co</mml:mi><mml:mo>/</mml:mo><mml:mi>Pt</mml:mi></mml:math>Nanodot Under the Assistance of rf Fields

Okamoto, Satoshi; Kikuchi, Nobuaki; Furuta, Masaki; Kitakami, Osamu; Shimatsu, T.

doi:10.1103/physrevlett.109.237209

Cited by 70 publications

(56 citation statements)

References 29 publications

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“…As shown in Fig. 3(d), the H rf dependence of H c is consistent with that of H swt calculated using an analytical model when the frequency of H rf is 16 GHz, at which the reduction in H c is maximized. Note that, in the calculation of H swt , the dynamical effect of the dipole-dipole interaction on the magnetization reversal 19,20 is not considered, although the static dipolar field is accounted for.…”

Section: Astroid Curves Under Applied Rf Fieldsupporting

confidence: 80%

“…[2][3][4][5][6][7][8][9][10][11] Microwave-assisted magnetization reversal (MAMR) has been widely investigated for application to perpendicular magnetic writing in hard disk drives. [12][13][14][15][16] Very recently, a frequency-dependent reduction in the switching field of the magnetization was experimentally reported for CoCrPt-SiO 2 granular films with perpendicular anisotropy. 17,18 Granular films have well-controlled microstructures consisting of small decoupled grains several nanometers in diameter.…”

Section: Introductionmentioning

confidence: 98%

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Frequency dependence of critical switching asteroid of CoCrPt–SiO2 granular film under 50-ns microwave impulse

Ishida¹,

Soeno²,

Sekiguchi³

et al. 2013

Journal of Applied Physics

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Understanding the dynamic process of microwave-assisted magnetization reversal (MAMR) in a dipole–dipole coupled granular perpendicular medium is essential for its application to future magnetic storage devices. We experimentally investigated the magnetization reversal process in CoCrPt–SiO2 granular films in terms of the dependence of the switching field on the strength of an applied in-plane radio-frequency magnetic field. The reversal process changed from non-uniform rotation to uniform rotation when the frequency increased toward the ferromagnetic resonance frequency. In the resonant condition, the switching field agreed well with a model assuming uniform rotation of the magnetization in each grain. The agreement suggests that the decoherence of ferromagnetic resonance due to a dynamic dipolar field is weak in adequately exchange-coupled granular films with a saturation magnetization of 415 emu/cm3. This finding is significant for the development of the practical medium necessary for MAMR writing.

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Section: Astroid Curves Under Applied Rf Fieldsupporting

confidence: 80%

Section: Introductionmentioning

confidence: 98%

Frequency dependence of critical switching asteroid of CoCrPt–SiO2 granular film under 50-ns microwave impulse

Ishida¹,

Soeno²,

Sekiguchi³

et al. 2013

Journal of Applied Physics

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“…On the other hand, in microwave-assisted magnetization reversal, microwaves with frequencies on the order of the ferromagnetic resonance (FMR) frequency efficiently supply energy to the ferromagnet, and reduce the direct field for switching. Typically, the switching field is reduced by less than half of the anisotropy field [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36].…”

Section: Introductionmentioning

confidence: 99%

Magnetization switching by current and microwaves

2016

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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.

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“…Microwave-assisted magnetization reversal [1][2][3][4][5][6][7][8][9][10] is a fascinating subject in magnetism for practical applications such as high-density recording. An oscillating field generated by microwaves excites a small-amplitude oscillation of the magnetization in the ferromagnet and significantly reduces the switching field to, typically, half of the uniaxial anisotropy field for an optimized microwave frequency.…”

mentioning

confidence: 99%

“…In previous works on microwave-assisted magnetization reversal, [1][2][3][4][5][6][7][8][9][10] the microwave source is isolated from the ferromagnet. Recently, however, an alternative system has been investigated both experimentally and numerically 11,12) in which a spin torque oscillator (STO) is used as the microwave source.…”

mentioning

confidence: 99%

Magnetization switching by microwaves synchronized in the vicinity of precession frequency

Taniguchi

2015

Appl. Phys. Express

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We propose a theoretical framework of a magnetization switching induced solely by a microwave. The microwave frequency is always close to but slightly different from the oscillation frequency of the magnetization. By efficiently absorbing energy from the microwave, the magnetization climbs up the energy landscape to synchronize the precession with the microwave. We introduced a dimensionless parameter ǫ determining the difference between the microwave frequency and the instant oscillation frequency of the magnetization. We analytically derived the condition of ǫ to switch the magnetization, and confirmed its validity by the comparison with numerical simulations.Microwave-assisted magnetization reversal 1-10) is a fascinating subject in magnetism for practical applications such as high-density recording. An oscillating field generated by microwaves excites a small-amplitude oscillation of the magnetization in the ferromagnet and significantly reduces the switching field to, typically, half of the uniaxial anisotropy field for an optimized microwave frequency. However, zero-field switching has not been reported experimentally; this is an outstanding problem in this field. A proposal of a theoretical possibility for switching induced solely by microwaves, as well as a deep understanding of its physical picture, will be an important guideline for further development in this field.In previous works on microwave-assisted magnetization reversal, 1-10) the microwave source is isolated from the ferromagnet. Recently, however, an alternative system has been investigated both experimentally and numerically 11,12) in which a spin torque oscillator (STO) is used as the microwave source. An oscillating dipole field emitted from the STO acts as microwaves on the ferromagnet and induces switching. Simultaneously, the dipole field from the ferromagnet changes the oscillation angle, as well as the oscillation frequency, in the STO. Therefore, in this situation, the microwave frequency from the STO depends on the magnetization direction in the ferromagnet. This motivated us to investigate the possibility of switching the magnetization solely by microwaves, the frequency of which depends on the magnetization direction itself. The purpose of this letter is to propose a theoretical framework for the switching process. Figure 1 schematically shows the energy landscape of a ferromagnet. The magnetization direction from the stable state is characterized by the energy E. When the magnetization arrives at the position at which the energy is E, the magnetic field excites precession of the magnetization on the constant energy curve with an oscillation frequency f (E). The FMR frequency, f FMR , corresponds to f (E) at the minimum energy state. Let us assume that the microwave frequency ν is close to but slightly different from the instant precession frequency f (E); i.e., ν = f (E) − ∆f with |∆f /f | ≪ 1. Because the instantaneous oscillation frequency f (E) changes with time during the magnetization dynamics, the microwave frequency ν shou...

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Switching Behaviors and its Dynamics of aCo/PtNanodot Under the Assistance of rf Fields

Cited by 70 publications

References 29 publications

Frequency dependence of critical switching asteroid of CoCrPt–SiO2 granular film under 50-ns microwave impulse

Frequency dependence of critical switching asteroid of CoCrPt–SiO2 granular film under 50-ns microwave impulse

Magnetization switching by current and microwaves

Magnetization switching by microwaves synchronized in the vicinity of precession frequency

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