Microwave assistance effect on magnetization switching in Co-Cr-Pt granular film

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

doi:10.1063/1.4830364

Cited by 32 publications

(30 citation statements)

References 27 publications

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“…Large objects (i.e., with dimensions substantially exceeding the exchange length) can exhibit a dramatically enhanced MAMR effect. 9 The proposed explanation is excitation of non-uniform modes; the similarity should be noted with modeling of the media with partially exchange decoupled layers, where a similarly large enhancement was found. 10,11 c. Most importantly, single spin theory offers a rather good prediction of the switching field as a function of the applied frequency; the observed reduction of coercivity and the optimal frequency are both slightly larger than the analytical limit, which can be taken into account by a minor adjustment in the formulas, as shown below in this paper.…”

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confidence: 55%

“…2 In the most severe case, which is excitation of non-uniform magnetization, it actually enhances the MAMR effect. 9 In all other cases, it appears that to sufficiently well describe the system is to enough to use a value of damping coefficient of b ¼ 0:06 or thereabout. It can be shown that for such values of damping, the formalism 2 can be altered by introducing a relatively minor reduction of the amplitude of the RF field, linearly proportional to the damping coefficient.…”

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confidence: 99%

“…Its transformation for the case of DC field applied parallel to the anisotropy axis is straightforward. 3,9 For a more general case, with non-zero DC field's angle and linearly polarized RF field, assuming that the RF field is applied at the optimal angle (effect of which will be discussed shortly), the same can be done only in a very approximate fashion, yielding…”

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confidence: 99%

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Physical principles of microwave assisted magnetic recording

Rivkin¹,

Benakli²,

Tabat³

et al. 2014

Journal of Applied Physics

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While the basic physics of Microwave Assisted Magnetization Reversal (MAMR) phenomenon is well established both theoretically and experimentally, its application in a practical magnetic recording environment was so far studied primarily with the help of micromagnetic recording models. In this work, we instead attempt to use analytical formulation and simple numerical models to understand the main challenges as well as benefits that are associated with such a system. It appears that the main difference between the previously introduced theory [G. Bertotti et al., Phys. Rev. Lett. 86, 724 (2001); K. Rivkin et al., Appl. Phys. Lett. 92, 153104 (2008); S. Okamoto et al., J. Appl. Phys. 107, 123914 (2010).] and recording environment is that both the RF and DC magnetic fields are applied at a substantial angle to the anisotropy axis. While the associated symmetry breaking prevents one from describing the reversal process explicitly, it is possible to approximate the solutions well enough to satisfactorily match numerical models both in the case of wire and Spin Torque Oscillator generated RF fields. This approach allows for physical explanation of various effects associated with MAMR such as high gradient of writeable anisotropy and reduction of track width, and offers a clear guidance regarding future optimization of MAMR recording.

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confidence: 55%

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confidence: 99%

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confidence: 99%

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Physical principles of microwave assisted magnetic recording

Rivkin¹,

Benakli²,

Tabat³

et al. 2014

Journal of Applied Physics

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“…15,18,19 While many experimental demonstrations of MAS have been reported so far, most of them are carried out on soft magnetic [20][21][22][23][24][25][26][27] or perpendicular magnetic elements [28][29][30] with the element size as large as several micrometers. Some experiments on granular type perpendicular recording media have been also reported, [31][32][33][34][35] but their switching processes still remain unclear. Very recently, we have carried out the MAS experiments on nanostructured dots of Co/Pt multilayers (Co/Pt in short) with perpendicular magnetic anisotropy.…”

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confidence: 99%

Size dependence of magnetization switching and its dispersion of Co/Pt nanodots under the assistance of radio frequency fields

Furuta¹,

Okamoto²,

Kikuchi³

et al. 2014

Journal of Applied Physics

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We have studied the dot size dependence of microwave assisted magnetization switching (MAS) on perpendicular magnetic Co/Pt multilayer dot array. The significant microwave assistance effect has been observed over the entire dot size D ranging from 50 nm to 330 nm examined in the present study. The MAS behavior, however, critically depends on D. The excitation frequency dependence of the switching field is well consistent with the spin wave theory, indicating that the magnetization precession in MAS is in accordance with the well defined eigenmodes depending on the dot diameter. The lowest order spin wave is only excited for D 100 nm, and then the MAS effect is well consistent with that of the single macrospin prediction. On the other hand, higher order spin waves are excited for D > 100 nm, giving rise to the significant enhancement of the MAS effect. The dispersion of MAS effect also depends on D and is significantly reduced for the region of D > 100 nm. This significant reduction of the dispersion is attributed to the essential feature of the MAS effect which is insensitive to the local fluctuation of anisotropy field, such as defect, damaged layer, and so on. V C 2014 AIP Publishing LLC. [http://dx.

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“…MAMR is a newly proposed technique of magnetization reversal in a nanostructured ferromagnet, where the microwaves excite an oscillation of the magnetization in a recording bit, resulting in a reduction of a direct magnetic field necessary to reverse the magnetization. Recently, MAMR was demonstrated experimentally 33,34,45 , where linearly or circularly polarized microwaves were generated from electric currents passing through coplanar wave guides. A currently exciting topic in MAMR is to replace the coplanar wave guides with the STO for high-density magnetic recording 28 .…”

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confidence: 99%

Spin torque oscillator for microwave assisted magnetization reversal

Taniguchi

2018

Jpn. J. Appl. Phys.

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A theoretical study is given for the self-oscillation excited in a spin torque oscillator (STO) consisting of an in-plane magnetized free layer and a perpendicularly magnetized pinned layer in the presence of a perpendicular magnetic field. This type of STO is a potential candidate for a microwave source of microwave assisted magnetization reversal (MAMR). It is, however, found that the self-oscillation applicable to MAMR disappears when the perpendicular field is larger than a critical value, which is much smaller than a demagnetization field. This result provides a condition that the reversal field of a magnetic recording bit by MAMR in nanopillar structure should be smaller than the critical value. The analytical formulas of currents determining the critical field are obtained, which indicate that a material with a small damping is not preferable to acheive a wide range of the self-oscillation applicable to MAMR, although such a material is preferable from the view point of the reduction of the power consumption.

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Microwave assistance effect on magnetization switching in Co-Cr-Pt granular film

Cited by 32 publications

References 27 publications

Physical principles of microwave assisted magnetic recording

Physical principles of microwave assisted magnetic recording

Size dependence of magnetization switching and its dispersion of Co/Pt nanodots under the assistance of radio frequency fields

Spin torque oscillator for microwave assisted magnetization reversal

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