Layered Antiferromagnetic Spin Structures of Expanded Face-Centered-Tetragonal Mn(001) as an Origin of Exchange Bias Coupling to the Magnetic Co Layer
P. J. Hsu, C.I. Lu, Y. H. Chu, B. Y. Wang, C. B. Wu, L. J. Chen, S. S. Wong,and Minn-Tsong Lin*
Spin structures of an exchange-coupled-bilayer system of expanded-face-centered-tetragonal (e-fct) Mn(001) ultrathin films grown on Co/Cu(001) were resolved by means of spin-polarized scanning-tunneling microscopy. With an in-plane spin-sensitive probe, a layered antiferromagnetic-spin ordering of Mn overlayers was evidenced directly. In addition, the spin frustration across the same Mn layer creating a narrow domain wall down to nanometer scale was also observed along the buried step of Co underlayers. According to the micromagnetic simulation, the step-induced domain-wall width is in agreement with the experimental results. Such in-plane layered antiferromagnetic-spin structures of e-fct Mn(001) provide uncompensated spins at the interface with Co underlayers and elucidate the mechanism of the corresponding exchange-bias field observed in the previous studies.