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

Dimensionality effects on epitaxial and polycrystalline Cr1−xRux alloy thin films and in Cr/Cr-Ru heterostructures are reported. X-ray analysis on Cr0.9965Ru0.0035 epitaxial films indicates an increase in the coherence length in growth directions (1 0 0) and (1 1 0) with increasing thickness (d), in the range 20≤d≤300 nm. Atomic force microscopy studies on these films shows pronounced vertical growth for d>50 nm, resulting in the formation of columnar structures. The Néel temperatures (TN) of the Cr0.9965Ru0.0035 films show anomalous behaviour as a function of d at thickness d≈50 nm. It is interesting to note that this thickness corresponds to that for which a change in film morphology occurs. Experiments on epitaxial Cr1−xRux thin films, with 0≤x≤0.013 and d=50 nm, give TN-x curves that correspond well with that of bulk Cr1−xRux alloys. Studies on Cr/Cr0.9965Ru0.0035 superlattices prepared on MgO(1 0 0), with the Cr layer thickness varied between 10 and 50 nm, keeping the Cr0.9965Ru0.0035 thickness constant at 10 nm, indicate a sharp decrease in TN 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.