Absence of spin-flip transition at the Cr(001) surface: A combined spin-polarized scanning tunneling microscopy and neutron scattering study

Abstract

The spin-density wave (SDW) on Cr(001) has been investigated at temperatures between $20--300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ by means of spin-polarized scanning tunneling microscopy (SP-STM). Although neutron-scattering data measured on the same crystal clearly show a spin-flip transition from a transversal (T)-SDW to a longitudinal (L)-SDW at the expected spin-flip (SF) temperature ${T}_{\mathrm{SF}}=123\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, no change was found on the Cr(001) surface with SP-STM. Throughout the entire temperature range the Cr(001) surface maintains a topological antiferromagnetic order with an in-plane magnetization that inverts between adjacent atomically flat terraces separated by monatomic step edges. The experimental results are interpreted by an absence of a spin-flip transition in the near-surface region probably driven by the surface anisotropy. The continuous connection of the surface T-SDW to the bulk L-SDW is accomplished by the formation of a 90\ifmmode^\circ\else\textdegree\fi{} domain wall just below the surface.