Merging droplets in double nano-contact spin torque oscillators

We demonstrate how magnetic droplet soliton pairs, nucleated by two separated nano-contact (NC) spin torque oscillators, can merge into a single droplet soliton. A detailed description of the magnetization dynamics of this merger process is obtained by micromagnetic simulations: A droplet pair with a steady-state in-phase spin precession is generated through the spin-transfer torque effect underneath two separate NCs, followed by a gradual expansion of the droplets volume and the out phase of magnetization on the inner side of the two droplets, resulting in the droplets merging into a larger droplet. This merger occurs only when the NC separation is smaller than a critical value. A transient breathing mode is observed before the merged droplet stabilizes into a steady precession state. The precession frequency of the merged droplet is lower than that of the droplet pair, consistent with its larger size. Merged droplets can again break up into droplet pairs at high enough magnetic field with a strong hysteretic response.Comment: accepted by Physical Review

Magnetization relaxation in (Ga,Mn)As ferromagnetic semiconductors

We describe a theory of Mn local-moment magnetization relaxation due to p-d kinetic-exchange coupling with the itinerant-spin subsystem in the ferromagnetic semiconductor (Ga,Mn)As alloy. The theoretical Gilbert damping coefficient implied by this mechanism is calculated as a function of Mn moment density, hole concentration, and quasiparticle lifetime. Comparison with experimental ferromagnetic resonance data suggests that in annealed strongly metallic samples, p-d coupling contributes significantly to the damping rate of the magnetization precession at low temperatures. By combining the theoretical Gilbert coefficient with the values of the magnetic anisotropy energy, we estimate that the typical critical current for spin-transfer magnetization switching in all-semiconductor trilayer devices can be as low as $\sim 10^{5} {\rm A cm}^{-2}$.Comment: 4 pages, 2 figures, submitted to Rapid Communication

Comprehensive Analysis of the Effect of Ausforming on the Martensite Start Temperature in a Fe-C-Mn-Si Medium-Carbon High-Strength Bainite Steel

The comprehensive effect of strain and ausforming temperature on the martensite start temperature (MS) of a medium-carbon bainite steel was investigated by thermal simulation, optical microscope, scanning electron microscope, etc. It is already known that small strain increases the MS, while larger strain decreases the MS. However, the effect of ausforming temperature on the MS has not been reported and clarified. In this study, the concepts of critical strain (εc) and saturated strain (εs) are proposed. The MS at the critical strain is equal to the MS of the nondeformed specimen. The saturation strain, which is first observed, is the strain value, and the MS does not further decrease with the increasing strain. The results show that the MS depends on the strain amount of ausforming but is not affected by the ausforming temperature. Moreover, with the increase of strain amount and ausforming temperature, the length of the martensite laths decreases. In addition, the hardness of the specimen increases with the increase of the ausforming strain amount, whereas the ausforming temperature has little effect on the hardness