Residual stress in Cr₉₉Al₁ polycrystalline thin films

The magnetic phase diagram of bulk Cr_100-xAl_x shows interesting behaviour close to the triple point concentration of x ≈ 2. Since the magnetic properties of Cr are influenced by dimensionality, stress and strain, this study focussed on the investigation of Cr₉₉Al₁ thin films prepared on fused silica substrates with thicknesses t varying from 29 to 452 nm using sputtering techniques. Resistance measurements covering the temperature range 2 to 400 K did not show any clear anomalies that could be indicative of changes in the magnetic ordering. X-ray diffraction (XRD) and atomic force microscopy (AFM) studies indicate the films are polycrystalline textured and that the 80 nm sample has the smallest grain size. In-plane stresses in these thin films were studied using the specialised XRD sin² φ-method. The results show that the stress varies with film thickness. The 29 nm sample has stress in the order of 833 MPa and with increasing film thickness the stress reaches 1471 MPa for the 80 nm layer, where after it systematically reduces for the thicker coatings to 925 MPa for the 452 nm film. The highest stress for the Cr₉₉Al₁ thickness sample series is seen in the film with the smallest grain size.