In 2013, scientists observed the phenomenon of unusual magnetoresistance (UMR) in magnetic heterojunctions, where the resistance of the heterojunction varies as the magnetic moment of the magnetic material rotates within a plane perpendicular to the current flow. This groundbreaking discovery marked a significant advancement in the realm of spintronics and holds profound implications for both the understanding and application of various spintronic effects. Initially, the microscopic mechanism underlying the UMR effect was thought to be tied to the spin Hall magnetoresistance (SMR). In this model, the spin current generated in heavy metals is reflected at the interface in a manner contingent on the orientation of the magnetic moment. This reflected spin current then re-enters the heavy metals, giving rise to a longitudinal conductance via the inverse spin Hall effect, ultimately altering the resistance. This theoretical framework laid the groundwork for comprehending the UMR effect.