Pure spin currents provide the possibility to control the magnetization state of conducting and insulating magnetic materials. They allow one to increase or reduce the density of magnons, and achieve ...coherent dynamic states of magnetization reminiscent of the Bose-Einstein condensation. However, until now there was no direct evidence that the state of the magnon gas subjected to spin current can be treated thermodynamically. Here, we show experimentally that the spin current generated by the spin-Hall effect drives the magnon gas into a quasi-equilibrium state that can be described by the Bose-Einstein statistics. The magnon population function is characterized either by an increased effective chemical potential or by a reduced effective temperature, depending on the spin current polarization. In the former case, the chemical potential can closely approach, at large driving currents, the lowest-energy magnon state, indicating the possibility of spin current-driven Bose-Einstein condensation.
We experimentally study nanowire-shaped spin-Hall nano-oscillators based on nanometer-thick epitaxial films of Yttrium Iron Garnet grown on top of a layer of Pt. We show that, although these films ...are characterized by significantly larger magnetic damping in comparison with the films grown directly on Gadolinium Gallium Garnet, they allow one to achieve spin current-driven auto-oscillations at comparable current densities, which can be an indication of the better transparency of the interface to the spin current. These observations suggest a route for improvement of the flexibility of insulator-based spintronic devices and their compatibility with semiconductor technology.
The energetic, crystallographic, and diffusion characteristics of vacancies and self-interstitial atoms (SIAs) in a face-centered cubic (FCC) copper crystal are obtained by molecular statics (MS) and ...molecular dynamics (MD). The temperature dependences of the diffusion and self-diffusion coefficients per self-point defect (SPD) are calculated in the temperature ranges of 750–1300 and 300–1300 K for vacancies and SIAs, respectively. The temperature dependences of the vacancy diffusion coefficients in the whole temperature range under consideration are well described by the Arrhenius dependence with a migration activation energy of 0.73 eV, and the corresponding dependences for SIAs in the temperature range 300–800 K, with a migration activation energy of 0.08 eV. The SPD diffusion is highly 3D at all temperatures. The obtained MD results are in good agreement with the known experimental data.
The properties of self di-interstitials—clusters formed by two self-interstitial atoms—in fcc copper crystal have been studied by the molecular statics and molecular dynamics methods. The formation ...energy (5.26 eV) and binding energy (0.83 eV) of the most energetically favorable configuration of a di-interstitial have been determined. The temperature dependences of the di-interstitial diffusion characteristics (diffusivity, the tracer correlation factor, the mean distance traveled between changes in migration direction, the frequency of migration direction changes, etc.) have been calculated for the temperature range of 300–1000 K; the temperature dependence of the di-interstitial dissociation lifetime has been calculated for the temperature range of 900–1100 K. Analytical dependences describing the calculated data have been proposed. The activation energy of di-interstitials dissociation is determined: 0.88 eV. For typical values of radiation defect sink strengths in radiation resistant materials (10
15
–10
16
m
–2
), temperature limits below which the overwhelming amount of di-interstitials are absorbed by the sinks before their dissociation are determined: 630–740 K.
The temperature dependences of diffusion characteristics of the irradiation-induced defects, namely, clusters of self-interstitial atoms (SIAs) containing up to five atoms, in bcc V (vanadium) have ...been studied by the method of molecular dynamics in the temperature range of 300–1000 K. The diffusion characteristics include the coefficient of diffusion, the tracer correlation factor, the average displacement before changing the direction of migration, and the frequency of changing the direction of migration. The values of the activation energy of diffusion and the activation energy of changing the direction of migration for the considered types of defects in different temperature ranges have been determined. The dependences of the mechanism of (1D vs 3D) diffusion of SIA clusters on the temperature and cluster size and their possible influence on the parameters of phenomenological models of changes in the microstructure of a material under irradiation (sink strengths of spherical absorbers) are discussed.
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