arXiv subjects

Shufeng Zhang

Publications and source records attributed to Shufeng Zhang.

24 records · Page 2Linked to original sources

arXiv2012

Magnetization dynamics at elevated temperatures

By using the quantum kinetic approach with the instantaneous local equilibrium approximation, we propose an equation that is capable of addressing magnetization dynamics for a wide range of temperatures. The equation reduces to the Landau-Lifshitz equation at low temperatures and to the paramagnetic Bloch equation at high temperatures. Near the Curie temperature, the magnetization reversal and dynamics depend on both transverse and longitudinal relaxations. We further include the stochastic fields in the dynamic equation in order to take into account fluctuation at high temperatures. Our proposed equation may be broadly used for modeling laser pump-probe experiments and heat assisted magnetic recording.

cond-mat.mes-hall↗

arXiv2008

Effects of current on nanoscale ring-shaped magnetic tunnel junctions

We report the observation and micromagnetic analysis of current-driven magnetization switching in nanoscale ring-shaped magnetic tunnel junctions. When the electric current density exceeds a critical value of the order of $6\times 10^{6}$A/cm$^2$, the magnetization of the two magnetic rings can be switched back and forth between parallel and antiparallel onion states. Theoretical analysis and micromagnetic simulation show that the dominant mechanism for the observed current-driven switching is the spin torque rather than the current-induced circular Oersted field.

cond-mat.mtrl-sci↗

arXiv2007

Kondo Resonance in the Presence of Spin-Polarized Currents

We propose an improved method of the equation of motion approach to study the Kondo problem in spin-dependent non-equilibrium conditions. We find that the previously introduced additional renormalization for non-equilibrium Kondo effects is not required when we use a proper decoupling scheme. Our improved formulation is then applied to address the spin-split Kondo peaks when a spin current injects into a Kondo system.

cond-mat.str-el↗

arXiv2006

Current-driven vortex domain wall dynamics by micromagnetic simulations

Current-driven vortex wall dynamics is studied by means of a two-dimensional analytical model and micromagnetic simulation. By constructing a trial function for the vortex wall in the magnetic wire, we analytically solve for domain wall velocity and deformation in the presence of the current-induced spin torque. A critical current for the domain wall transformation from the vortex wall to the transverse wall is calculated. A comparison between the field- and current-driven wall dynamics is carried out. Micromagnetic simulations are performed to verify our analytical results.

cond-mat.mtrl-sci↗

arXiv2004

Identification of transverse spin currents in noncollinear magnetic structures

We show that the transverse components of spin current in a ferromagnet is linked to an off diagonal spin component of the transmission matrix at interfaces;it has little to do with the mismatch of band structures between dissimilar metals. When we take account of this component,not considered in prior analyses, we find spin torque comes from a region of at lease 3 nm around an interface.

cond-mat.mes-hall↗

arXiv2002

A self-consistent treatment of non-equilibrium spin torques in magnetic multilayers

It is known that the transfer of spin angular momenta between current carriers and local moments occurs near the interface of magnetic layers when their moments are non-collinear. However, to determine the magnitude of the transfer, one should calculate the spin transport properties far beyond the interface regions. Based on the spin diffusion equation, we present a self-consistent approach to evaluate the spin torque for a number of layered structures. One of the salient features is that the longitudinal and transverse components of spin accumulations are inter-twined from one layer to the next, and thus, the spin torque could be significantly amplified with respect to treatments which concentrate solely on the transport at the interface due to the presence of the much longer longitudinal spin diffusion length. We conclude that bare spin currents do not properly estimate the spin angular momentum transferred between to the magnetic background; the spin transfer that occurs at interfaces should be self-consistently determined by embedding it in our globally diffuse transport calculations.

cond-mat.mes-hall↗