Current-induced vortex-vortex switching in a nanopillar comprising two Co nano-rings

Yang, Tianyu; Hirohata, Atsufumi; Hara, Masahiro; Kimura, Takashi; Otani, Y.

doi:10.1063/1.2710185

Cited by 15 publications

(10 citation statements)

References 22 publications

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“…The field is then lowered again, which nucleates a CW vortex in the top disc, according to the Oersted field of the negative applied current. Correspondingly, an OV-DV configuration is obtained at the point indicated by the yellow star 25 .…”

Section: Resultsmentioning

confidence: 99%

Spin-torque-induced dynamics at fine-split frequencies in nano-oscillators with two stacked vortices

et al. 2015

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The gyrotropic rotation around the equilibrium position constitutes the fundamental excitation of magnetic vortices in nanostructures. The frequency of this mode varies with material and sample geometry, but is independent of the vortex handedness and its core direction. Here, we demonstrate that this degeneracy is lifted in a spin-torque oscillator containing two vortices stacked on top of each other. When driven by spin-polarized currents, such devices exhibit a set of dynamic modes with discretely split frequencies, each corresponding to a specific combination of vorticities and relative core polarities. The fine splitting occurs even in the absence of external fields, demonstrating that such devices can function as zero-field, multi-channel, nano-oscillators for communication technologies. It also facilitates the detection of the relative core polarization and allows for the eight non-degenerate configurations to be distinguished electrically, which may enable the design of multi-state memory devices based on double-vortex nanopillars.

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Section: Resultsmentioning

confidence: 99%

Spin-torque-induced dynamics at fine-split frequencies in nano-oscillators with two stacked vortices

et al. 2015

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“…16 More recently exchange bias ͑EB͒ has been explored in combination with a homogeneous external field to control reversal in Co/IrMn elliptical dots 17 and rings. 18 A combination of spin torque and Oersted field has been used to switch the chirality in pseudospin valve rings 19 and the spin torque effect alone has been predicted to switch the chirality in vortex-supporting spin-valve disks. 20 EB ͑Ref.…”

Section: Introductionmentioning

confidence: 99%

Magnetization reversal in circularly exchange-biased ferromagnetic disks

et al. 2009

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We investigate the reversal behavior of circularly exchange-biased micron-sized bilayer disks of Permalloy ͑Py͒/IrMn and CoFe/IrMn. A circular exchange bias is induced by imprinting the vortex configuration of the ferromagnetic layer into the IrMn when the disks are cooled in zero external field through the blocking temperature of IrMn. The resulting circular exchange bias has a profound effect on the reversal behavior of the ferromagnetic magnetization. In Py/IrMn disks the reversal takes place via vortex motion only, and the behavior is controlled by the exchange bias; it is reversible over a range of small fields and the vortex maintains a single chirality throughout reversal, determined by the chirality of the exchange bias. In CoFe/IrMn disks the non-negligible magnetocrystalline anisotropy causes a reversal via both vortices and domain walls resulting in a finite coercivity, and the behavior is controlled by microstructure. We verify that circular exchange bias does not give rise to a hysteresis loop shift. It lowers coercivity with respect to the field-cooled case, and in Py/IrMn disks it even causes completely reversible magnetic behavior. In both Py/IrMn and CoFe/IrMn disks, circular exchange bias removes the randomness ͑i.e., stochastic processes due to thermal activation͒ inherent in singlelayer ferromagnetic disks and causes the magnetic behavior to be reproducible over time.

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“…As a source of unidirectional anisotropy, it has been shown that exchange bias ͑EB͒ can be used to control the reversal mechanisms in patterned nanomagnets. 17 While the majority of work on rings has been concerned with single layer, 16,18 or pseudospin valve structures, [19][20][21] there is limited reported work on EB bilayer rings [22][23][24] especially at low temperatures.…”

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confidence: 99%

Magnetic properties of exchange biased Co/CoO elongated nanoring arrays

Tripathy

Adeyeye

2009

Journal of Applied Physics

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We present a systematic study of the magnetic properties of exchange biased Co͑25 nm͒ / CoO͑t CoO ͒ / Cu͑2 nm͒ elongated nanoring arrays. The reversal mechanism in the exchange biased nanorings is directly compared to that of unbiased nanorings of identical geometry at varying temperatures. We observe that along the field cooling direction, the exchange biased nanorings exhibit reversal via shifted vortex states with enhanced magnitudes of onion→ vortex and vortex→ reverse onion transition fields. The magnitude of exchange bias field is also found to be strongly dependent on the CoO layer thickness t CoO , and decreases monotonically with increasing t CoO . Due to the interplay between the exchange and Zeeman energies, the exchange bias field could also be varied by adjusting the field cooling strength.There has been an emerging scientific interest in the magnetization reversal mechanisms of patterned nanomagnets with precisely controlled geometry and interelement spacing 1 due to potential applications in a wide range of magnetoelectronic devices such as magnetic random access memory, 2 read head sensors, 3 programmable logic devices, 4 and ultrahigh density patterned storage media. 5 From a fundamental viewpoint, nanomagnets offer by virtue of their low dimensionality, a wide range of magnetic properties which are not observed in their continuous bulk counterparts, especially when the size becomes comparable to or smaller than certain characteristic length scales such as spin diffusion length, carrier mean free path, and magnetic domain wall width. 6 Therefore, the influence of shape and size on the magnetic properties of square, 7-9 circular, 10,11 elliptical, 12,13 diamond, 14 and triangular 15 shaped nanomagnets has been widely investigated.Recently, a substantial amount of study has also been conducted on ring shaped nanomagnets driven by its technological importance and appealing magnetic states, namely, the flux-closure or "vortex" state in which the magnetization is oriented circumferentially around the ring, either clockwise or counterclockwise, and the bidomain or "onion" state in which two halves of the ring magnetization adopt opposite circulations, with each half separated by 180°domain walls. 16 For successful implementation in any magnetoelectronic device, it is imperative to achieve a consistent and experimentally tunable switching mechanism in such ring elements. As a source of unidirectional anisotropy, it has been shown that exchange bias ͑EB͒ can be used to control the reversal mechanisms in patterned nanomagnets. 17 While the majority of work on rings has been concerned with single layer, 16,18 or pseudospin valve structures, 19-21 there is limited reported work on EB bilayer rings 22-24 especially at low temperatures.In this work, a systematic study of the magnetic properties of EB Co/CoO elongated nanoring arrays is presented as a function of temperature. We observe that the magnetization reversal in nanorings is significantly modified due to EB. The evolution in EB field H E is also inves...

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Current-induced vortex-vortex switching in a nanopillar comprising two Co nano-rings

Cited by 15 publications

References 22 publications

Spin-torque-induced dynamics at fine-split frequencies in nano-oscillators with two stacked vortices

Spin-torque-induced dynamics at fine-split frequencies in nano-oscillators with two stacked vortices

Magnetization reversal in circularly exchange-biased ferromagnetic disks

Magnetic properties of exchange biased Co/CoO elongated nanoring arrays

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