Ultrathin All‐in‐One Spin Hall Magnetic Sensor with Built‐In AC Excitation Enabled by Spin Current

Abstract

fascinating spintronic effects are spinorbit torque (SOT) [10] and spin Hall magnetoresistance (SMR) [11] in ferromagnet (FM)/heavy metal (HM) bilayers. Taking advantage of these intriguing effects, recently we have demonstrated an AMR/ SMR sensor (hereafter we call it SMR sensor considering the fact that SMR is dominant) with the SOT effective field as the built-in linearization mechanism, [12,13] which effectively replaces the sophisticated linearization mechanism employed in conventional MR sensors. [14] However, as the sensors were driven by DC current, we still faced the same issues as commercial AMR sensors, that is, DC offset and domain motion induced noise. Here, we demonstrate that, by introducing AC excitation, we achieved an all-in-one magnetic sensor which embodies multiple functions of AC excitation, domain stabilization, rectification detection, and DC offset cancellation, and importantly, all these features are realized in a simplest possible structure which consists of only an ultrathin NiFe/Pt bilayer. Such kind of integrated AC excitation and rectification are not possible in conventional AMR sensors. The sensors are essentially free of DC offset with negligible hysteresis and low noise (with a detectivity of 1 nT Hz −1/2 at 1 Hz). Through a few proof-ofconcept experiments, we show that these sensors promise great potential in a variety of low-field sensing applications including navigation, angle detection, and wearable electronics.When a charge current passes through a ferromagnet (FM)/ heavy metal (HM) bilayer, it brings about two novel spintronic effects, namely, the SOT [10] and SMR. [11] Both SOT and SMR share the same origin, i.e., the spin current generated in the HM layer by the spin Hall effect (SHE). [15][16][17] The spin current is transverse to the charge current and therefore causes spin accumulation at both the FM/HM interfaces and side surfaces of HM. The spin accumulation at the interfaces is partially absorbed by the FM layer, resulting in a torque on its magnetization, i.e., the SOT. Although the exact mechanism still remains debatable, both Rashba [18] and SHE [15][16][17] are commonly believed to play a crucial role in giving rise to the SOT in FM/ HM bilayers. There are two types of SOTs, one is field-like (FL) and the other is damping-like (DL); the latter is similar to spin transfer torque. Phenomenologically, the two types of torques can be modelled by

Spin Torque Gate Magnetic Field Sensor

“…This allows us to demonstrate proof-of-concept of operation of the STG sensor in both the deterministic and stochastic switching regimes. The sensors exhibit good linearity in the field range of ±3-10 Oe, which is almost 10 times larger than the spin Hall magnetoresistance (SMR) sensor demonstrated by us previously which uses the FL effective field as the built-in linearization mechanism [25][26][27][28][29] . In addition, the output voltage is also about order of magnitude larger than that of SMR sensor.…”

Platinum composition dependence of spin-orbit torque in (Fe0.8Mn0.2)1−xPtx single-layer ferromagnet

“…It is particularly effective in evaluating the FL effective field in the FM with in-plane anisotropy as demonstrated in our previous work on spin Hall magnetoresistance (SMR) sensors. [28][29][30] The signal related to the DL torque is negligible as magnetization is mostly in-plane. Although one can extend the technique to measure the DL torque by applying a large out-of-plane field, 31 its sensitivity is around two orders of magnitude smaller, which adversely compensates the advantage of the bridge method.…”

Inverse Spin Hall Effect in Electron Beam Evaporated Topological Insulator Bi2Se3 Thin Film

“…Spintronics has been the major focus topic of research in last three decades . Devices based on spintronics have shown potential applications in the data storage devices, non‐volatile magnetic random‐access memory (MRAM), spin torque oscillators, magnonics, spin Hall magnetic sensor, spin orbit torque (SOT)‐induced magnetic switching, etc. Giant magnetoresistance (GMR)‐based devices utilized spin polarized current to switch the magnetization .…”