Magnetism in low-dimensions is a fascinating topic: Even in apparently simple systems -such as homoatomic monolayers- the nearest neighbor distance, the symmetry and the hybridization with the substrate can play a crucial role for the magnetic properties. This may lead to a variety of magnetic structures, from the ferromagnetic and antiferromagnetic state to much more complex spin structures.
Spin-polarized scanning tunneling microscopy (SP-STM) combines magnetic sensitivity with high lateral resolution and therefore grants access to such complex magnetic order with unit cells on the nanometer scale. Recently, different intricate magnetic structures have been observed in pseudomorphic homoatomic 3d monolayers on late 5d transition metal substrates [1,2].
Here, we present spin-averaged and spin-polarized scanning tunneling microscopy data for the pseudomorphic Mn monolayer on W(001). A uniaxial periodic structure on the nanometer-scale is observed in spin-averaging measurements, which implies a lateral modulation of the electronic structure within this structurally homogeneous monolayer. Due to the four-fold symmetry of the surface, two rotational domains are possible. We interpret this periodicity in the spin-averaged data as varying spin-orbit coupling of differently aligned magnetic moments leading to small changes in the band structure [3]. To verify this assumption we apply SP-STM to directly image the magnetic structure. The uniaxal magnetic structure found has twice the size of the electronic modulation, which is expected for magnetic compared to spin-orbit coupling periodicidy. Experiments within an external magnetic field show that the magnetic moments rotate from an in-plane direction through the out-of-plane direction, resulting in a spin spiral state.
[1] K. von Bergmann et al., Phys. Rev. Lett. 96, 167203 (2006).
[2] M. Bode et al., submitted.
[3] M. Bode et al., Phys. Rev. Lett. 89, 237205 (2002). |