A strong anisotropic magnetoresistance
(AMR) effect induced by
spin–orbit coupling is the basis for constructing a highly
sensitive and reliable magnetic sensor. Presently, effective AMR enhancement
in traditional films focuses on the modulation of the lattice or charge
degree of freedom, leading to a general AMR ratio below 4%. Here,
we demonstrate a different strategy to strengthen the AMR effect by
tuning the orbital degree of freedom. By inserting an oxygen-affinitive
Hf layer into a Ta/MgO/NiFe/MgO/Ta multilayer film, Fe–O orbital
hybridization at the MgO/NiFe interface was modulated to trigger an
effective orbital reconfiguration of Fe. In turn, the number of holes
in the in-plane symmetric d orbits of Fe increased substantially,
facilitating the s–d electron scattering to enhance the AMR
ratio to 4.8%. By further micromachining the film into a Wheatstone
bridge, we constructed a sensing element that displayed an ultrahigh
sensitivity of 2.7 mV/V/Oe and a low noise detectability of 0.8 nT/√Hz.
These findings help to advance the development of orbit-governed AMR
sensors and provide an alternative method for tuning other orbit-related
physical effects.