The ultrasensitive anomalous Hall effect induced by interfacial oxygen atoms redistribution

Abstract

Improved weak magnetic field detection has been achieved by the ultrasensitive linear Anomalous Hall effect (AHE) in MgO/CoFeB/X/Ta/MgO (X: Hf or Gd) multilayers. The Anomalous Hall sensitivity (Sv) has been tuned by effective oxygen migration assisted interfacial oxygen atoms redistribution. For the sample with 0.2 nm Hf insertion, the Anomalous Hall sensitivity (Sv) is 16 182 Ω/T at the as-deposited state, 560% larger than that of the sample with no insertion (2470 Ω/T). However, the value of Sv for the sample with 0.2 nm Gd insertion is only up to 6837 Ω/T. An ultrahigh value of Sv (28 282 Ω/T) is obtained for the sample with 0.2 nm Hf insertion by a further annealing process. Interfacial structural results indicate that different linear AHE behavior originate from various interfacial oxygen atoms distribution states, which can be ascribed to different oxygen migration processes. The strong oxygen affinity capability of metallic Hf leads to the bidirectional interfacial oxygen migration. However, only unidirectional interfacial oxygen migration can be observed in the sample with 0.2 nm Gd insertion. This study will provide an effective way to improve the AHE-based sensors for weak magnetic field detection.