Investigation of spin-orbit torque switching with stray field from in-plane magnet

Utilizing the stray field from an in-plane magnet under the heavy metal layer is promising to realize field-free spin-orbit torque (SOT) switching. However, the stray field is unevenly distributed, which may significantly reduce the reliability of SOT switching, especially in memory array. In this paper, we investigate the variations in stray field generated by in-plane magnets with different sizes, finding that as the length of the in-plane magnetic strip increases, the field strength at the middle of the strip decreases, but its uniformity improves. We then simulate SOT switching of magnetic tunnel junction (MTJ) with stray field assistance. The results show that the stray field applied to a single MTJ reaches 9.15 mT, enabling field-free SOT switching at a current density of 118 MA/cm². In the array with two MTJs, switching occurs at a current density of 121 MA/cm². However, the stray field on the middle MTJ drops to only 0.88 mT in the three-MTJ array, resulting in a much longer switching time of 6 ns and indeterministic switching. Thus, the in-plane magnet scheme is not applicable to array structures consisting of three or more MTJs. These findings provide a significant foundation for the practical applications of the in-plane magnet in field-free MTJ-array structures.