Fig. 5: Exchange coupling between CoFeB and FeRh moments across the interface.

Sketches for the exchange coupling between CoFeB and FeRh moments across the interface for FeRh a in the AF state and b in the FM state. CoFeB moments and rotatable FeRh moments are represented by black and red double arrows, respectively. Uncompensated and compensated FeRh moments are represented by gray and white arrows, respectively. The springs illustrate the possible exchange coupling between them. c Unit vectors of uniaxial magnetic anisotropy for the single SM layer (black dots) and fourfold symmetrical anisotropy for the AF (red dots) and FM (blue dots) HM layers in the Monte Carlo simulation. d Calculated coercivity as a function of the field orientation for the single SM layer (black dots) and the SM/AF (red dots) and SM/FM (blue dots) bilayers. The oscillatory curves are the sinusoidally fitting results. The simulation indicates that the interfacial exchange coupling may result in a fourfold magnetic anisotropy of CoFeB layers with easy magnetization axes collinear with the magnetocrystalline anisotropy of FeRh, which is predicted to be e along the FeRh〈110〉 direction in the AF state and f along the FeRh〈100〉 direction in the FM state.