Spin-polarized scanning tunneling spectroscopy study of epitaxial iron(001) layers on bct-manganese(001)

In this work, the correlation between layer spacing and magnetic coupling of successive Fe layers on the bct-Mn by means of spin-polarized scanning microscopy and spectroscopy (SP-STM/STS) is studied. In ultra-high-vacuum, Fe(001) epitaxial layers are grown at room temperature (RT) on bct-Mn(001) and are deposited on a single crystalline Fe(001)-whisker. These layers show a bct structure with the same in-plane lattice constant as the substrate and the bct-Fe. With ferromagnetic Fe-coated W tips, the magnetic structures of the first to the eighth Fe layer at RT are also studied. Since the substrate Mn layers couple antiferromagnetically, the first Fe layers grown on the odd and even Mn layers show magnetic contrast. Surprisingly, the contrast is also observed between the second and first Fe layers. This means that the first Fe layer also couples antiferromagnetically with the second layer. Similar SP-STS measurements for Fe films with other thicknesses are done and results show that the first to fourth Fe layers on bct-Mn have non-collinear helical magnetic coupling. The inter-layer exchange coupling constant J_k turns out to be strongly correlated to the step height or interlayer distance d, i.e., J_k<0 for d>0.155 nm and J_k>0 for d<0.155 nm. Also, it is shown from SP-STS results that J_k2<0 for 0k changes its sign, i.e., J_k<0 for k<4 and J_k>0 for k>5.