Time-resolved zero field vortex oscillations in point contacts

Devolder, T.; Kim, Joo-Von; Crozat, P.; Chappert, C.; Manfrini, Mauricio; Kampen, M. van; Roy, W. Van; Lagae, Liesbet; Hrkac, G.; Schrefl, T.

doi:10.1063/1.3170234

Cited by 52 publications

(51 citation statements)

References 10 publications

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“…The nanocontact STOs presented in this study can also sustain gyrotropic vortex motion 47,48 , generating frequencies primarily below 1 GHz and showing operation in zero applied magnetic field 49 . Whereas we have not investigated the gyrotropic motion in detail, we here present an example of such operation.…”

Section: Resultsmentioning

confidence: 82%

Mutually synchronized bottom-up multi-nanocontact spin–torque oscillators

et al. 2013

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Spin-torque oscillators offer a unique combination of nanosize, ultrafast modulation rates and ultrawide band signal generation from 100 MHz to close to 100 GHz. However, their low output power and large phase noise still limit their applicability to fundamental studies of spin-transfer torque and magnetodynamic phenomena. A possible solution to both problems is the spin-wave-mediated mutual synchronization of multiple spin-torque oscillators through a shared excited ferromagnetic layer. To date, synchronization of high-frequency spin-torque oscillators has only been achieved for two nanocontacts. As fabrication using expensive top-down lithography processes is not readily available to many groups, attempts to synchronize a large number of nanocontacts have been all but abandoned. Here we present an alternative, simple and cost-effective bottom-up method to realize large ensembles of synchronized nanocontact spin-torque oscillators. We demonstrate mutual synchronization of three high-frequency nanocontact spin-torque oscillators and pairwise synchronization in devices with four and five nanocontacts.

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Section: Resultsmentioning

confidence: 82%

Mutually synchronized bottom-up multi-nanocontact spin–torque oscillators

et al. 2013

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“…Interestingly, we note that the device emits a significant power, even at zero field, as compared to microwave emission previously observed in the absence of any applied field [10,20]. The spectral linewidth, presented in Fig.…”

mentioning

confidence: 88%

Dynamics of two coupled vortices in a spin valve nanopillar excited by spin transfer torque

Locatelli

Naletov

Grollier

et al. 2011

Applied Physics Letters

120

107

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We investigate the dynamics of two coupled vortices driven by spin transfer. We are able to independently control with current and perpendicular field, and to detect, the respective chiralities and polarities of the two vortices. For current densities above J = 5.7 * 10 7 A/cm 2 , a highly coherent signal (linewidth down to 46 kHz) can be observed, with a strong dependence on the relative polarities of the vortices. It demonstrates the interest of using coupled dynamics in order to increase the coherence of the microwave signal. Emissions exhibit a linear frequency evolution with perpendicular field, with coherence conserved even at zero magnetic field.The lowest energy mode of vortex dynamics corresponds to the gyrotropic motion of the core around its equilibrium position. This mode have been studied extensively (for a review see Ref.[1]), and very recent works demonstrated that it could also be stimulated by spin transfer torque [2][3][4][5]. The resulting microwave signals are characterized by narrow linewidths (about 1 MHz) [6,7] and, for structures based on magnetic tunnel junctions instead of metallic nanopillars, large output powers [8], making these spin transfer vortex oscillators good candidates for applications as nanoscale frequency synthesizers.The reported observation of microwave emission without any applied magnetic field raises questions about the actual sources of spin torque, in particular about the role played by the static and/or dynamic behavior of the polarizer [9,10]. Here, we intentionally design samples so that both the active layer and the polarizer layer can contain a magnetic vortex, thus leading to a more complex but interesting situation of coupled vortices. The problem of interacting vortices has been rarely treated even for a field-driven excitation [11][12][13][14]21] and never for a current induced excitation. Taking benefit of this 2-vortices configuration, our objective is to establish some selection rules for the observation of highly coherent coupled vortices in terms of their relative chiralities and polarities. To do that, we first demonstrate our capability to control independently the vortices chiralities and polarities, and to detect the resulting configuration through dc transport measurements. Consequently, we can provide some clear evidence that the microwave features associated with the coupled dynamics greatly depend upon the characteristics of each vortex, notably here their relative core polarities.

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“…Our probe of choice is the nucleation of a dynamical vortex state [9,20,21] as induced by pulsed currents. It has been shown previously [13] that the vortex nucleation probability can be described by an Arrhénius law with a single activation energy E a (I) which depends only on the total pulse amplitude.…”

mentioning

confidence: 99%

Understanding Nanoscale Temperature Gradients in Magnetic Nanocontacts

et al. 2012

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We determine the temperature profile in magnetic nanocontacts submitted to the very large current densities that are commonly used for spin-torque oscillator behavior. Experimentally, the quadratic current-induced increase of the resistance through Joule heating is independent of the applied temperature from 6 K to 300 K. The modeling of the experimental rate of the current-induced nucleation of a vortex under the nanocontact, assuming a thermally-activated process, is consistent with a local temperature increase between 150 K and 220 K. Simulations of heat generation and diffusion for the actual tridimensional geometry were conducted. They indicate a temperatureindependent efficiency of the heat sinking from the electrodes, combined with a localized heating source arising from a nanocontact resistance that is also essentially temperature-independent. For practical currents, we conclude that the local increase of temperature is typically 160 K and it extends 450 nm about the nanocontact. Our findings imply that taking into account the currentinduced heating at the nanoscale is essential for the understanding of magnetization dynamics in nanocontact systems.

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Time-resolved zero field vortex oscillations in point contacts

Cited by 52 publications

References 10 publications

Mutually synchronized bottom-up multi-nanocontact spin–torque oscillators

Mutually synchronized bottom-up multi-nanocontact spin–torque oscillators

Dynamics of two coupled vortices in a spin valve nanopillar excited by spin transfer torque

Understanding Nanoscale Temperature Gradients in Magnetic Nanocontacts

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