An investigation of the microstructure and magnetic properties of pulse-layered Co2MnSi thin films

The magnetic properties of nanocrystalline Co2MnSi thin films grown on GaAs(lO0) and glass substrates using the pulsed-laser deposition (PLO) technique are investigated. The influence of varying the substrate temperature (between 23°C and 500°C, (using a fluence of25 Jcm-2)) and then the laser fluence (up to 40 Jcm-2 , (with substrates heated to-170°C)) are considered with regard to the films' microstructures, compositions and magnetic attributes. The results are used to develop a model of magnetic hysteresis, based on the Stoner-Wohlfarth theory and adapted to model the conditions within the films. Theoretical simulations modelling the experimentally obtained magnetization curves are conducted, from which information indicative of the films' anisotropic properties and their spin populations are ascertained. Microstructural analysis, carried out using 0120 X-ray diffraction, established the films to be nanogranular in nature, with (median) grain diameters varying between 5 nm and 11 nm. Auger electron spectroscopy revealed that films with stoichiometries similar to that of the desired Co2MnSi could be obtained when using deposition laser fluences of approximately 20- 25 Jcm-2• The importance of controlling the substrate temperature was also demonstrated as textured growth arose when the GaAs substrates were heated above 100°C during deposition, and glass above 150°C. These conditions were believed sufficient for the promotion of crystalline growth, without subsurface and resputtering processes reducing the films' qualities. SQUID magnetometry was used to measure the magnetic moment of the ferromagnetic samples, whilst subjected to an externally applied magnetic field. The films exhibited square magnetization curves, with high remanence and sharp switching, found to arise from magnetic coupling of the single-domain grains. The high crystallinity was chiefly responsible in generating anisotropies of the order of 20 kJm-3, and gaining good magnetic exchange, with many films demonstrating effective moments close to the expected 5 μn per formula unit, indicative of good spin propagation.