Tunnel Magnetoresistance Detection of Skyrmions

Skyrmions have been proposed for racetrack memory, but there are still many questions about the best way to detect them electronically. Mumax³ micromagnetic simulations were used to determine the core direction and chirality of skyrmions. A spin polarized current was used to move a Néel skyrmion down a racetrack that contains a circular magnetic dot above it to detect the core direction by tunnel magnetoresistance (TMR). When the skyrmion core and dot magnetizations are parallel, the skyrmion diameter grows slightly as it approaches the dot, since the dipolar field tends to orient misaligned spins. The spatial field gradient due to the dot causes a repulsive deflection around the dot and there is a transient drop in resistance. When the skyrmion core and dot magnetization are antiparallel, the skyrmion slightly shrinks in diameter as it approaches the dot, and there is an attractive interaction. The time profile then shows a transient. The chirality of a skyrmion is detected by an in-plane magnetized synthetic antiferromagnet detector, which creates smaller stray field compared to a single layered dot. A peak-dip or dip-peak feature in the time profile represents the chirality of the detected skyrmion.