Detection of a symmetric circular gyration of the vortex core via the second-order harmonic magnetoresistance oscillation

Sugimoto, Satoshi; Hasegawa, N.; Niimi, Yasuhiro; Fukuma, Yasuhiro; Kasai, S.; Otani, Y.

doi:10.7567/apex.7.023006

Cited by 7 publications

(11 citation statements)

References 25 publications

(40 reference statements)

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“…This value matches closely with the simulated f G = 128 MHz at H || = 0 (see below). Note that in circular disks, a rectification peak is not generated for H || = 0 due to the symmetry of the core trajectory around the center of the disk which results in the generated voltage time-averaging to zero 26,43 . In contrast, the chopped disk geometry leads to the core's equilibrium position being shifted away from the circular center of the element even for H || = 0 [ Fig.…”

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confidence: 99%

Chirality-mediated bistability and strong frequency downshifting of the gyrotropic resonance of a magnetic vortex due to dynamic destiffening

et al. 2017

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We demonstrate an enhanced, bidirectional, in-plane magnetic field tuning of the gyrotropic resonance frequency of a magnetic vortex within a disk by introducing a flat edge. When the core is in its vicinity, the flat edge locally reduces the core's directional dynamic stiffness for movement parallel to the edge. This strongly reduces the net dynamic core stiffness, leading to the gyrotropic frequency being significantly less than when the core is centered (or located near the round edge). This leads to the measurable range of gyrotropic frequencies being more than doubled and also results in a clear chirality-mediated bistability of the gyrotropic resonance frequency due to what is effectively a chirality-dependence of the core's confining potential.

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confidence: 99%

Chirality-mediated bistability and strong frequency downshifting of the gyrotropic resonance of a magnetic vortex due to dynamic destiffening

et al. 2017

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“…1(a)]. Although the 2f signal can be directly probed 33 , a finite rectified voltage can be achieved by laterally displacing the equilibrium core position using a static in-plane field 31,32 . The changes in resistance for left and right displaced cores are then unequal [ Fig.…”

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confidence: 99%

Electrical measurement of magnetic-field-impeded polarity switching of a ferromagnetic vortex core

et al. 2016

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Vortex core polarity switching in NiFe disks has been evidenced using an all-electrical rectification scheme. Both simulation and experiments yield a consistent loss of the rectified signal when driving the core at high powers near its gyrotropic resonant frequency. The frequency range over which the loss occurs grows and shifts with increasing signal power, consistent with non-linear core dynamics and periodic switching of the core polarity induced by the core attaining its critical velocity. We demonstrate that core polarity switching can be impeded by displacing the core towards the disk's edge where an increased core stiffness reduces the maximum attainable core velocity.

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“…Since the resistance of the ferromagnetic sample depends upon the contribution of the sample magnetization along (or perpendicular to) the current flow direction, the gyrotropic motion of the vortex core is followed by a periodic change in the resistance of the magnetic sample. As the vortex core moves symmetrically around the center of the magnetic element, its resistance [R = R 0 + ∆R cos(2ωt + φ)] changes with twice the frequency of the excitation current [106,107]. This can simply be explained by the sketch shown in Fig.…”

Section: Amr In Vortex Structuresmentioning

confidence: 99%

Electrical determination of vortex state in submicron magnetic elements

et al. 2015

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Vortex structures in confined geometries are currently under close scrutiny due to their unique properties associated with their spatial confinement and the nonuniform distribution of the magnetization. The magnetic vortex is characterized by two boolean topological quantities: circulation (clockwise or counterclockwise c = ± 1) of the in-plane magnetization and polarity (up or down, p = ± 1) of the vortex core. These four degenerate states are quite stable and can accelerate the development of more compact and high performance magnetic memory devices. Thus an understanding of their dynamical behavior and a way to electrically detect these states is a major requirement for their development. Progress can be achieved by combining theoretical calculations, micromagnetic simulations and experimental approaches. The phenomenon of spin transfer torque is exploited to excite the lowest frequency (gyro) mode of the vortex core confined in a submicron magnetic (Permalloy -N i 81 F e 19 ) element. The gyrotropic motion of the vortex core leads to a periodic change in the magnetization and hence its resistance: due to the anisotropic magnetoresistance (AMR) effect. This periodic change in resistance combines with the excitation current and generates a periodic homodyne voltage signal. An external static magnetic field is applied to break the symmetry and to rectify the homodyne voltage signal which we measure in a nanovoltmeter. It is found that the sign of the rectified AMR signal depends upon the handedness (cp) of the vortex structure. Micromagnetic simulations provide better understanding and are in good agreement with our experimental results. Additionally, vortex dynamics in these samples is investigated in a Scanning Transmission X-ray Microscope (STXM) with a temporal (< 100 ps) and spatial ( 30 nm) resolution which allows us to verify the resonance frequency of the magnetic element as well as the power range to excite the vortex core. The AMR based technique thus can be used to detect the circulation and the polarity of the vortex state electrically and could open a route to implement magnetic vortex elements in memory and storage hierarchies.The phenomenon of Spin Motive Force (SMF) has also been studied by micromagnetic simulations. It is found that, in a particular configuration, the SMF signal shows a phase difference of 180 degrees for two polarities of the vortex core, when the voltage probe contacts are located parallel to the excitation rf field direction. No phase shift is observed in the perpendicular case. In addition, a 180 degree phase difference is observed for different circulations of the vortex structure.Therefore, this could also be a possible way to determine polarity and circulation of the magnetic vortex by carefully examining the phase relation of the SMF generated voltage signals. An attempt has also been made to measure the SMF experimentally. However, due to the small expected signal unambiguous detection of SMF was not successful so far. 4

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Detection of a symmetric circular gyration of the vortex core via the second-order harmonic magnetoresistance oscillation

Cited by 7 publications

References 25 publications

Chirality-mediated bistability and strong frequency downshifting of the gyrotropic resonance of a magnetic vortex due to dynamic destiffening

Chirality-mediated bistability and strong frequency downshifting of the gyrotropic resonance of a magnetic vortex due to dynamic destiffening

Electrical measurement of magnetic-field-impeded polarity switching of a ferromagnetic vortex core

Electrical determination of vortex state in submicron magnetic elements

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