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

Abstract

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(100) and (110) with increasing thickness(d), in the range 20≤d≤300nm. Atomic force microscopy studies on these films show pronounced vertical growth for d>50nm, 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 (100), with the Cr layer thickness varied between 10 and 50nm, keeping the Cr0.9965Ru0.0035 thickness constantat 10nm, indicate a sharp decrease in TN as the Cr separation layers reaches a thickness of 30nm; ascribed to spin density wave pinning in the Cr layers for d< 30nm by the adjacent CrRu layers.