Nanoscale layer-selective readout of magnetization direction from a magnetic multilayer using a spin-torque oscillator

Suto, Hirofumi; Nagasawa, Tooru; Kudo, Kiwamu; Mizushima, Koichi; Sato, Rie

doi:10.1088/0957-4484/25/24/245501

Cited by 39 publications

(35 citation statements)

References 38 publications

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“…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.…”

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confidence: 99%

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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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“…As mentioned above, the present model is motivated by a ferromagnet coupled to an STO. 11,12) To strictly investigate the possibility of switching, the coupled LLG equations between the ferromagnet and the STO should be solved. 13) It is, however, difficult to solve such LLG equations analytically because of their complexity.…”

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confidence: 99%

Magnetization switching by microwaves synchronized in the vicinity of precession frequency

Taniguchi

2015

Appl. Phys. Express

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“…In magnetic recording, it is necessary to manipulate and sense nanometer-sized magnetizations within the nanosecond timescale. For this kind of nanometer-and nanosecondscale FMR excitation and measurement, a spin-torque oscillator (STO) [11][12][13][14] can be used [3,4], which is a nanometersized microwave field generator with a typical oscillation frequency of approximately 0.1 GHz to several tens of gigahertz. In write operations, an RL is selectively switched by the combination of the microwave field from the STO and a field from a write pole, which is a multilayer version of microwave-assisted magnetization switching [17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

“…This read method is therefore called resonance reading. The basic principles have been experimentally demonstrated [3]. An STO suitable for resonance reading in HDDs has been proposed, and its transient magnetization dynamics during the resonance reading for the case of a single recording layer have been investigated by using micromagnetic simulation [5].…”

Section: Introductionmentioning

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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“…[1][2][3][4][5][6][7] Spin-torque-induced oscillation was first demonstrated by Kiselev et al for a nanopillar consisting of a Co= Cu=Co junction in 2003. 1) They obtained an output power of less than 1 nW, which was too small for practical applications, and a spectral linewidth as large as 0.6 GHz.…”

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Spin-torque-induced oscillation at zero bias field in a magnetoresistive nanopillar with a free layer with first- and second-order uniaxial anisotropy

Arai

Matsumoto

Yuasa

et al. 2015

Appl. Phys. Express

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Spin-torque-induced magnetization dynamics in a nanopillar having a perpendicularly magnetized free layer with firstand second-order uniaxial anisotropy and an in-plane magnetized reference layer is studied theoretically on the basis of the macrospin model. It is shown that in the presence of second-order uniaxial anisotropy, self-oscillation is induced even at zero bias magnetic field. Analytical expressions for the threshold current, condition of the second-order anisotropy constant required for oscillation, and current dependence of the oscillation frequency are obtained.

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Nanoscale layer-selective readout of magnetization direction from a magnetic multilayer using a spin-torque oscillator

Cited by 39 publications

References 38 publications

Magnetization switching by microwaves synchronized in the vicinity of precession frequency

Magnetization switching by microwaves synchronized in the vicinity of precession frequency

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

Spin-torque-induced oscillation at zero bias field in a magnetoresistive nanopillar with a free layer with first- and second-order uniaxial anisotropy

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