Island-assisted interface alloying and magnetic polarization at submonolayer V/Cr(001) interfaces

Island-assisted interface alloying was observed during submonolayer deposition on Cr(001) substrates at 525 K. Scanning tunneling spectroscopy suggests atomic interchange at the center of the islands during the early stages of growth, giving rise to a Cr core in the center of the island and a gradually increasing V concentration toward the island rim. The existence of a VCr alloy with equiatomic composition is concluded by comparing tunneling spectra measured at the island rim with density-functional theory calculations. Coalescence of the initial islands gives rise to inhomogeneous alloying at monolayer coverage. Antiferromagnetic coupling between the islands and the Cr(001) substrate is found for coverages up to 0.50 atomic layers. At higher coverages, no magnetic contrast was observed.

Figure 1

(Color online) Topography STM maps of V islands deposited on Cr(001) substrates at 525 K with coverages from 0.12 to 1.65 AL. Layer-by-layer growth is observed.

Figure 2

(Color online) (a) Differential conductance curves measured on the substrate at different positions on one of the islands for 0.09 AL coverage [see (b) and (c) for a topographic images]. A Gaussian fitting of the $dI/dU$ curves shows the different contributions (dotted lines). (d) DOS simulations for a single V AL on Cr(001) and for a single AL of equiatomic CrV alloy on Cr(001).

Figure 3

(Color online) (a) Topography, (b) chemical contrast $dI/dU$ map measured at a bias voltage of $U=+0.4\text{V}$, and (c) spin-resolved $dI/dU$ map measured at $U=-0.4\text{V}$ corresponding to the same area of a sample with 0.24 AL V coverage. Clearly, antiferromagnetic coupling is found between substrate and islands.

Figure 4

(Color online) Spin resolved $dI/dU$ maps of the V films deposited on Cr(001) at 525 K with coverages from 0.12 to 1.65 AL measure with a bias voltage of $-0.4\text{V}$. Antiferromagnetic coupling between the Cr substrate and the islands grown on top is clearly observed for coverages up to 0.85 AL.