Influence of growth morphology on the Neel temperature of CrRu thin films and heterostructures

摘要

Dimensionality effects on epitaxial and polycrystalline Cr_(1-x)Ru_x alloy thin films and in Cr/Cr-Ru heterostructures are reported. X-ray analysis on Cr_(0.9965)Ru_(0.0035) epitaxial films indicates an increase in the coherence length in growth directions (10 0) and (110) with increasing thickness (d), in the range 20≤d≤300nm. Atomic force microscopy studies on these films shows pronounced vertical growth for d>50nm, resulting in the formation of columnar structures. The Neel temperatures (T_N) of the Cr_(0.9965)Ru_(0.0035) films show anomalous behaviour as a function of d at thickness d≈50nm. It is interesting to note that this thickness corresponds to that for which a change in film morphology occurs. Experiments on epitaxial Cr_(1-x)Ru_x thin films, with 0≤x≤0.013 and d = 50nm, give T_N-x curves that correspond well with that of bulk Cr_(1-x)Ru_x alloys. Studies on Cr/Cr_(0.9965)Ru_(0.0035) superlattices prepared on MgO(100), with the Cr layer thickness varied between 10 and 50 nm, keeping the Cr_(0..9965)Ru_(0.0035) thickness constant at 10 nm, indicate a sharp decrease in T_N as the Cr separation layers reaches a thickness of 30 nm; ascribed to spin density wave pinning in the Cr layers for d<30 nm by the adjacent CrRu layers.