Considerable Anisotropy Magnetoresistance by Oxygen-Mediated Spin State Manipulation in a Highly Textured Multilayer for Ultrasensitive Sensor Application

Abstract Spin state manipulation in anisotropy magnetoresistance (AMR) materials is key to improving their transport property for constructing highly sensitive and direction-resolvable magnetic sensors. Currently, the mainstream strategy of tuning the transport property focuses on the modulation of charge by controlling the physical scattering path of conduction electrons, limiting the AMR ratio below 4% and linear sensitivity lower than 1.5%/Oe. This paper reports a strategy of manipulating the orbital degree of freedom to achieve an unprecedently large AMR effect. Here, we achieved the oxygen tunability of the spin state in a highly textured MgO/NiFe/MgO/Ta multilayer by regulating the Fe–O orbital hybridization in the lattice-texture-tunable coordination environment. The (111)- and (110)-textured films exhibit a low-spin state, offering enough unoccupied d↑ states to enhance the s–d↑ scattering and improve the transport property. On this basis, a considerable AMR ratio of 8.7% and a high linear sensitivity of 2.7%/Oe were achieved, helping to construct an ultrasensitive sensor with sensitivity approaching 3.3 mV/V/Oe, which is the highest value among the commercialized AMR sensors. These results provide a feasible idea for developing the orbital-modulated AMR sensor and clarify the physical origin of magneto-ion-spin coupling.