Hafnium Layer Help Create Multilayered Ultrasensitive Magnetic Sensors

Hafnium inserted in a multilayer increases anomalous Hall effect sensitivities by 883% and improves capabilities for detecting weak magnetic fields.

Magnetic sensors

Magnetic sensors play a critical role in driving new advanced technology with industrial, military, and aerospace applications. Now new research has discovered a way to further enhance the anomalous Hall sensitivity in multilayered magnetic sensors.

In the past decade, substantial work has gone into developing anomalous Hall effect (AHE) in ferromagnetic materials, because it provides high signal-to-noise ratio and fast response frequency, while simultaneously being easy to make. However, these materials are not sensitive enough to detect weak magnetic fields, which limits their possible applications.

Peng et al. created an ultrasensitive film by sandwiching a thin layer of hafnium between other commonly used ferromagnetic materials, in the arrangement of MgO/CoFeB/Hf/Ta/MgO. Their results showed that the hafnium layer raised the sensitivity of the sample by 560%, and by 883% when the sample was annealed. They also experimented with a layer of gadolinium in another annealed sample, which also improved the sensitivity by 701%.

Using X-ray photoelectron spectroscopy, the authors found that the linear AHE behavior originates in the interfacial oxygen atoms distribution state, meaning that the difference between the two samples was due to the difference in migration of interfacial oxygen atoms. The metallic hafnium, with its strong affinity for oxygen, was able to migrate interfacial oxygen from both the Ta and CoFeB layers it was located between, while gadolinium was only able to migrate oxygen unidirectionally from the Ta layer.

The new ultrasensitive multilayers dramatically improved their abilities to detect weak magnetic fields. The results suggest that the anomalous Hall sensitivity of thin ferromagnetic films can be further tuned for future applications.