Proximity effect coupled V Cr superlattices

V_mCr_n superlattices, where m and n denote the number of atomic planes of V and Cr in each layer, with m equal to 98, 147, 175 and 197 and n varying between 3 and 100 have been prepared. The films were grown in an ultra-high vacuum chamber (base pressure ≈1×10^-9 Torr) equipped with dual e-guns and a rotating substrate holder. Films were grown at 250°C on "c" cut sapphire substrates. The zero field transition temperature and parallel upper critical field of the films have been measured. A dimensional crossover in the parallel upper critical field is observed at n equal to about 80. The zero field transition temperature data has been modeled using the procedures and of Werthamer and Auvil and Ketterson. The magnetic scattering time, τ, in the Cr layers has been found to be dependent on the vacuum during deposition: 4.5×10^-14 sec for films deposited at ≤ 4×10^-7 Torr and 5.5×10^-14 sec for films deposited at ≤ 4×10^-8 Torr. For the V₁₇₅Cr_x series with n >- 80 the best fits occur for infinite scattering time τ.