Speaker
Would you like to <br> submit a short paper <br> for the Conference <br> Proceedings (Yes / No)?
yes
Level for award<br> (Hons, MSc, <br> PhD)?
MSc
Apply to be<br> considered for a student <br> award (Yes / No)?
YES
Main supervisor (name and email)<br>and his / her institution
Dr C J Sheppard
cjshepppard@uj.ac.za
University of Johannesburg
Abstract content <br> (Max 300 words)<br><a href="http://events.saip.org.za/getFile.py/access?resId=0&materialId=0&confId=34" target="_blank">Formatting &<br>Special chars</a>
The Néel temperature (TN) in thin film Cr coatings is strongly influenced by dimensionality effects, as well as strain and stress [1]. In an investigation of Cr thin films with thickness (t) varied between 20 and 320 nm deposited on fused silica substrates, the TN values obtained from resistivity measurements indicate an increase with thickness as expected [1]. However, it is noted that the TN ≈ 460 K obtained for the t = 320 nm sample, is considerably higher than the transition temperature of 311 K obtained in bulk pure Cr. This behavior is unexpected, but incidentally corresponds with TN = 475 K obtained for the CSDW-P Néel transition in bulk Cr when influenced by stresses introduced by cold working [3,4]. Since stresses are well known to influence the physical properties of materials [1,2], amongst others the magnetic properties, this study is now extended to investigations of the in-plane stresses in these thin films. This is done using the specialised X-ray diffraction sin2&psi–method [2,5,6]. With this technique, variations in the lattice plane spacing is accurately determined from the precisely measured (310) Bragg peak position as function of systematically increased tilt angles, &psi, from the surface normal to as close as achievable to the in-plane direction. The in-plane residual strain present in the coating (&epsilon) is determined from the slope of a linear plot through the fractional change in the plane spacing (or Bragg peak position) versus sin2&psi plots. Residual stress (&sigma) are calculated from the &epsilon versus sin2&psi data by incorporating the elastic properties of the coating material. The results indicate tensile stresses in all the samples. Results will be used to correlate the TN values to the stresses in the coatings.
References:
[1] Zabel H 1999 J. Phys. Condens. Matter 11 9303
[2] Genzel CH 2004 J. of Neutron Research 12 233
[3] Fawcett E 1988 Rev. Mod. Phys. 60 209
[4] Prinsloo ARE et al. 2010 J. Magn. Magn. Mat. 322 1126
[5] Society for Automotive Engineering, Residual Stress Measurement by XRD, 2nd edition 1971 SAE J748a
[6] Noyan IC, Cohen JB, Residual Stress, Measurement by Diffraction and Interpretation, Springer-Verlag, New York, 1987
