Spin transfer torque bias (STTB) due to domain wall resistance in an infinitely long ferromagnetic nanowire

The shift of a magnetization loop along the magnetic field axis for a ferromagnetic (FM)/anti-ferromagnetic (AFM) system when it is cooled through Neel temperature of AFM layer is called exchange anisotropy or exchange bias. Here, using micromagnetic simulations we propose that spin transfer torque (STT) mechanism would indeed be helpful in realizing the shift of the magnetization loop along magnetic field axis through domain wall (DW) resistance for an infinitely long FM nanowire without having AFM layer, which we call as spin transfer torque bias (STTB). Essentially, STTB is realized on both positive and negative magnetic field axes by varying the angle between spin polarized current and Zeeman field from 0 degrees to 180 degrees respectively and the origin is attributed to helical motion of the DW. However, we do not see STTB at 90 degrees due to coherent rotation of domain. We also ascertain that STTB is also a function of magnetic anisotropy, current density, polarization strength and non-adiabatic STT term. Variation in STTB for different FM systems such as Fe2CoSi, Ni80Fe20 and Fe is attributed to a change in DW width. We believe that present results would lead to a new dimension in the field of spintronics.

Automated summary

In this study, we propose that the spin transfer torque mechanism can be used to shift the magnetization loop along the magnetic field axis in an infinitely long ferromagnetic nanowire without an antiferromagnetic layer. We call this phenomenon spin transfer torque bias. The occurrence of spin transfer torque bias depends on the angle between the spin-polarized current and the Zeeman field, and is attributed to the helical motion of the domain wall.