The growth mode and magnetism at V(001)/Cr(001) interfaces are still controversial and in recent years have attracted considerable theoretical and experimental interest since they strongly affect the properties of multilayered structures prepared with these materials. Both V and Cr are bcc 3d transition metals with approximately half-band filling. Cr exhibits antiferromagnetism along the <001> direction which converts the (001) surfaces to ferromagnetic (001) planes that couple antiferromagnetically from layer to layer. Interestingly, it has been theoretically predicted that a single V layer on Cr couples antiferromagnetically to Cr with an induced V moment of 2.1 μ_B/atom, but drastically reducing the Cr magnetic moment[1]. Previous reports using Mössbauer spectroscopy[2] applied to Cr/V multilayers have given direct experimental evidence for a reduction of the Cr magnetic moment near the interface region. In addition, recent neutron scattering experiments have shown that proximity effects in Cr/V multilayers lead to the appearance of a 50 Å magnetically dead Cr layer near the interfaces[3].

Despite the interest in V/Cr(001) interfaces, possible magnetic polarization of V by proximity to the antiferromagnetic Cr(001) substrate has not been yet fully investigated. We report on our spin-polarized scanning tunneling microscopy (SP-STM ) studies on subatomic layer coverings of V on Cr(001) substrates and experimentally demonstrate antiferromagnetic coupling between V islands and the Cr(001) underlying surface. V was evaporated on Cr(001) substrates under ultra-high vacuum conditions (base pressure in the low 10-11 mbar) and at 250 ºC, temperature reported as optimum to achieve high quality multilayers with abrupt interfaces2. V coverages ranging from 0.1 to 1.5 atomic layers (AL) where explored. Antiparallel coupling between the V islands and the Cr(001) substrate is found, with the magnetic contrast disappearing when the V islands start to coalesce for increasing coverages starting at 0.9 AL. In addition, using Scanning Tunneling Spectroscopy and density functional theory calculations, it was found that during the early stages of growth the islands exhibit radial symmetry in their chemical composition, with Cr-rich composition in the center and V-rich regions at the rims. Interestingly, for higher coverages such islands coalesce evidencing an island assisted interface alloying mechanism.

[1.] G. Bihlmayer, T. Asada and S. Blugel, Phys. Rev. B 62 (18), 11937 (2000).

[2.] K. Mibu et al., J. Magn. Magn. Mat. 226-230 (Part 2), 1785-1787 (2001).

[3.] E. Kravtsov et al., Phys. Rev. B 76 (2), 024421 (2007).