Exchange coupling in epitaxial SmCo(1100)/NdCo exchange-spring bilayers

We have studied the exchange coupling behavior of the epitaxial Nd–Co(1100)/Sm–Co exchange-spring bilayers. A shifted and asymmetric magnetic hysteresis loop of Nd–Co was recorded at room temperature with the exchange field Hex=−625 Oe. The magnitude of Hex increases with increasing temperature from 300 to 350 K, which is due to the temperature-dependent magnetic anisotropy of the Nd–Co layer, and decreases with decreasing temperature because of the spin reorientation of the Nd–Co layer around 250 K. The coercive field of the pinned Nd–Co(1000 A) layer was not varied systematically by exchange coupling, compared with that of the free single layer. The temperature dependence of Hex above 300 K has been simulated using a one-dimensional model. The result suggests that one can enhance Hex, hence, the maximum size of the soft phase for the effective exchange-spring coupling, by tailoring the magnetic anisotropy of the soft phase.