Domain walls in thermal gradients — Entropic torque and angular momentum transfer

Numerical simulations as well as analytical calculation based on the Landau-Lifshitz-Bloch equation of motion are performed in this study for thermal micromagnetic calculations. The focus is to investigate domain wall velocity and discuss the analogy to the case of domain wall motion caused by spin transfer torque where two additional torque terms (adiabatic and non-adiabatic) are added to the equation of motion. It is found that for the case of thermally driven domain wall motion, an effective exchange field is created by the temperature gradient that acts on the domain wall similar to the spin torque terms. Analyses also indicate that the effect of entropic term should be much larger than that of angular momentum transfer from the magnon current.