Theoretical study of thermally activated magnetization switching under microwave assistance: Switching paths and barrier height

Suto, Hirofumi; Kudo, Kiwamu; Nagasawa, Tooru; Kanao, Taro; Mizushima, Koichi; Sato, Rie; Okamoto, Satoshi; Kikuchi, Nobuaki; Kitakami, Osamu

doi:10.1103/physrevb.91.094401

Cited by 28 publications

(32 citation statements)

References 21 publications

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“…(6). The fact that the direction of this torque is expressed by a triple vector product, similarly to the spin torque, indicates that the mathematical analysis for spin torque driven magnetization dynamics can be applied to the analysis of microwave-assisted magnetization reversal or vice versa [37,38,63]. It should be emphasized that this torque moves the magnetization to the initial equilibrium state when the microwaves rotate in the same direction with the magnetization precession; i.e., it prevents the switching.…”

Section: B Competition Between Spin Torque and Microwavesmentioning

confidence: 99%

“…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%

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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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Section: B Competition Between Spin Torque and Microwavesmentioning

confidence: 99%

Section: Balance Currentmentioning

confidence: 99%

Magnetization switching by current and microwaves

2016

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“…For implementing this recording technique, MAS has recently been studied extensively both experimentally and theoretically. [29][30][31][32][33][34][35][36][37] As a means of generating a microwave field, integrating an STO in the gap between a main pole and a trailing shield in a write element is mainly considered. Another way is to introduce a microwave electrical signal close to a medium using a waveguide built in a write element.…”

Section: Layer-selective Manipulation Of Magnetization Direction Usinmentioning

confidence: 99%

Three-dimensional magnetic recording using ferromagnetic resonance

Suto

Kudo

Nagasawa

et al. 2016

Jpn. J. Appl. Phys.

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To meet the ever-increasing demand for data storage, future magnetic recording devices will need to be made three-dimensional by implementing multilayer recording. In this article, we present methods of detecting and manipulating the magnetization direction of a specific layer selectively in a vertically stacked multilayer magnetic system, which enable layer-selective read and write operations in three-dimensional magnetic recording devices. The principle behind the methods is ferromagnetic resonance excitation in a microwave magnetic field. By designing each magnetic recording layer to have a different ferromagnetic resonance frequency, magnetization excitation can be induced individually in each layer by tuning the frequency of an applied microwave magnetic field, and this selective magnetization excitation can be utilized for the layer-selective operations. Regarding media for three-dimensional recording, when layers of a perpendicular magnetic material are vertically stacked, dipolar interaction between multiple recording layers arises and is expected to cause problems, such as degradation of thermal stability and switching field distribution. To solve these problems, we propose the use of an antiferromagnetically coupled structure consisting of hard and soft magnetic layers. Because the stray fields from these two layers cancel each other, antiferromagnetically coupled media can reduce the dipolar interaction.

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“…In addition, is chosen such that the effective perpendicular field is smaller for SL2 than for SL1. The smaller effective perpendicular field leads to larger excitation by the microwave field from the STO [15,16].…”

Section: Parametersmentioning

confidence: 99%

Layer-selective detection of magnetization directions from two layers of antiferromagnetically-coupled magnetizations by ferromagnetic resonance using a spin-torque oscillator

Kanao

Suto

Mizushima

et al. 2020

Journal of Magnetism and Magnetic Materials

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A B S T R A C TWe use micromagnetic simulation to demonstrate layer-selective detection of magnetization directions from magnetic dots having two recording layers by using a spin-torque oscillator (STO) as a read device. This method is based on ferromagnetic resonance (FMR) excitation of recording-layer magnetizations by the microwave field from the STO. The FMR excitation affects the oscillation of the STO, which is utilized to sense the magnetization states in a recording layer. The recording layers are designed to have different FMR frequencies so that the FMR excitation is selectively induced by tuning the oscillation frequency of the STO. Since all magnetic layers interact with each other through dipolar fields, unnecessary interlayer interferences can occur, which are suppressed by designing magnetic properties of the layers. We move the STO over the magnetic dots, which models a read head moving over recording media, and show that changes in the STO oscillation occur on the one-nanosecond timescale.

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Theoretical study of thermally activated magnetization switching under microwave assistance: Switching paths and barrier height

Cited by 28 publications

References 21 publications

Magnetization switching by current and microwaves

Magnetization switching by current and microwaves

Three-dimensional magnetic recording using ferromagnetic resonance

Layer-selective detection of magnetization directions from two layers of antiferromagnetically-coupled magnetizations by ferromagnetic resonance using a spin-torque oscillator

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