The structural and magnetic properties of MnBi and exchange coupled MnBi/Fe films

The structural and magnetic properties of MnBi and MnBi/Fe films prepared by magnetron sputtering and in situ vacuum annealing are investigated. MnBi film is highly c-axis textured with perpendicular anisotropy. The out-of-plane coercivity increases with temperature, which reaches to 15 kOe and 21 kOe at 300 K and 400 K, respectively. For exchange coupled MnBi/Fe films, when the thickness of Fe layer is thin, the hysteresis loops show single-phase-like reversal behavior due to the effective interfacial exchange coupling. In comparison with MnBi film, the remanent magnetization enhances. The maximum energy product also improves from 7.6 MGOe to 8.0 MGOe at 300 K, and from 5.7 MGOe to 6.1 MGOe at 400 K. As the thickness of Fe layer exceeds the critical dimension, the two-step reversal behavior is observed, indicating the decoupling of soft Fe layer and neighboring hard MnBi layer. - Highlights: • MnBi film shows perpendicular anisotropy with highly c-axis textured. • At 400 K, MnBi film shows a higher (BH)_max than MnBi magnet due to perpendicular anisotropy. • (BH)_max of MnBi/Fe film is enhanced due to exchange coupling. • A step emerges on the demagnetization curve of MnBi/Fe film as temperature goes up