Large Exchange Bias due to the Spin Density Wave Antiferromagnet Cr in a Fe/Cr(100) Bilayer

Abstract

The temperature and cooling-field dependences of an exchange bias field in a 4-nm Fe/16.2-nm Cr(100) bilayer were studied in this work. Unexpectedly, the magnetic hysteresis loop exhibits a large shift, by as much as -100 Oe, at low temperatures below 40 K, which becomes gradually reduced with increasing cooling field and temperature. This large exchange bias results from an interfacial exchange coupling between the remnant Fe moments and the in-plane uncompensated Cr moments. This uncompensated spin density wave in the Cr layer is produced by interface disorders, such as epitaxial strain due to the lattice mismatch between the MgO substrate and the Cr layer and interface roughness. The cooling field possibly decreases the exchange bias due to the transition from the uncompensated spin state to a partially compensated spin state of Cr spins at the interface.