Superconducting properties and preferred orientations of epitaxial growth in V/Cr multilayers

We investigated the superconducting properties of V/Cr multilayers with the different preferred orientations of (100) and (110). These samples were grown epitaxially on MgO (100) and Al₂O₃ (1120) single-crystal substrates. The Cr layer thickness was varied from d_cr=2 to 140Å at a constant V layer thickness of 300 Å. In (100) V/Cr, the critical temperature T_c abruptly drops with increasing d_Cr from 5 to 40 Å and shows a plateau above 40 Å. In (110) V/Cr, T_c gradually decreases up to d_Cr=80 Å and keeps a higher value than in (100). For the temperature dependence of parallel upper critical fields, H_c2∥(T), the 3D-to-2D dimensional crossover phenomenon takes place in d_Cr=10∼25 Å for (100) V/Cr and 10∼70 Å for (110) V/Cr. 2D behavior of H_c2∥(T), which implies the decoupling of superconducting V layers by the Cr layer, is achieved in the range of d_Cr above 40 Å for (100) and 80 Å for (110). The ratio of H_c2⊥ to H_c2⊥ for (100) V/Cr is enhanced in comparison with that for (110). Our results indicate that the strong pair-breaking effect operates at the interfaces of (100) V/Cr.