Applying a difference ratio method in spin-polarized scanning tunneling microscopy to determine crystalline anisotropies and layer-to-layer spin coupling in Cr(0 0 1) c(2 × 2)

We grew 7930 ± 93 nm thick Cr(0 0 1) films by molecular beam epitaxy on MgO(0 0 1) substrates achieving an atomically smooth staircase morphology. The c(2 × 2) surface structure of the Cr(0 0 1) surface was found via atomically resolved scanning tunneling microscopy images and dI/dV spectroscopy. A practical method of interpreting spin-polarized scanning tunneling microscopy dI/dV images was developed and applied to the c(2 × 2) Cr(0 0 1) surface structure. An in-plane 180° spin reversal between atomic layers creating a topological antiferromagnetic structure was observed. The spin quantization axes of the c(2 × 2) spins were found to depend on the atomic staircase with spin aligned along the [1 0 0], [0 1 0], and [1 1 0] crystal axes.