Structure and magnetism of ultra-thin chromium layers on W(110)

We have investigated the structural and magnetic properties of ultra-thin Cr films on W(110) by means of low-energy electron diffraction intensity-versus-voltage (LEED IV) data acquired using selected-area diffraction within a low-energy electron microscope (LEEM), spin-polarized scanning tunneling microscopy (SP-STM), and ab initio calculations. The interlayer distances as obtained from LEED IV data are compared to ab initio calculations. The first-principles calculations predict very different interlayer spacings depending on whether the Cr films are antiferromagnetic or non-magnetic. Only antiferromagnetic spin ordering leads to interlayer spacings similar to the experimental spacings determined by LEED IV. This strongly suggests that films of one, two and three atomic layers of Cr on W(110) have antiferromagnetic short-range order. SP-STM data confirm this finding: the Cr monolayer on W(110) shows characteristic stripes along the [001] direction due to the antiferromagnetic order of nearest-neighbor Cr atoms. Additionally, the SP-STM data of the Cr monolayer reveal a periodically varying magnetic amplitude that peaks every 7.7 +/- 0.5 nm. On thick Cr(110) films the signature of an incommensurate spin density wave, existing in two different orientations, is found. We also compare the LEED IV and ab initio relaxations of bare W(110) and bulk-like Cr(110) surfaces.