Semi-quantitative evaluation of stacking faults in pseudo-hcp thin films by laboratory-scale in-plane x-ray diffraction

Measurement of the stacking faults (SFs) formed in a pseudo-hexagonal closed packed (pseudo-hcp) film is proposed using a laboratory-scale x-ray diffractometer. The pseudo-hcp structure includes (1?1?1)-oriented face-centred-cubic (fcc), c-plane oriented hcp and their mediate structures with the SFs. Diffractions from the (11.0) and (10.0) planes, DH and DL, were observed in the in-plane x-ray diffraction (XRD) profiles of the pseudo-hcp materials. The structure factor revealed that DH and DL originate from the number of total atomic layers and the imbalance of the number of A, B and C atomic layers, respectively. Therefore, the intensity ratio of DH to DL, corrected by Lorentz and atomic scattering factors (corrected IL/IH), is defined as the degree of SFs for pseudo-hcp materials from the stacking probability, independent of thickness, compositional atoms and lattice constants. Theoretical values of the corrected IL/IH are 0.25 for perfect hcp stacking and 0 for perfect fcc stacking and statistical calculations revealed that this index is very sensitive to the approach of perfect hcp stacking order rather than that of perfect fcc stacking order. By applying this evaluation to experimentally sputtered thin films, it was clarified that: (1) in Pt based alloy films, addition of Cr, Mo and W is found to stabilize ?A?B?A? stacking, (2) the corrected IL/IH for a c-plane oriented Co film is only 0.04, which corresponds to an hcp stacking probability of 0.9 for a pure Co film and (3) in both cases of Co?Ir and Co?Pt alloy films, the atomic-layered structure approaches perfect hcp stacking for additive alloying element contents of 22?25?at%, which is considered to be one of the factors contributing to the large absolute value of uniaxial magnetocrystalline anisotropy.