English abstract
The primary aim of the present research work was to control the growth of Fe/Cu magnetic multilayers (MLs) on the nanometric scale. Fe/Cu MLs have been prepared by thermal evaporation method. The rate of deposition of individual layers of Fe and Cu has been determined from crystal quartz monitor measurements and grazing angles X-ray diffraction (GXRD) spectra simulation. GXRD results confirmed the successful growth of a multilayered structure. One of the objectives of this work was to investigate the structure and phase adopted by thin Fe layers. Previous work on Fe/Cu system prepared by other methods has shown that Fe may adopt different phases dependent upon the thickness of Fe and the condition of deposition. Structural properties of Fe/Cu MLs have been investigated by using high angle X-ray diffraction (HXRD) and transmission electron microscopy with very high resolution (HRTEM) down to 0.1 mm. Fe/Cu MLs were found to be polycrystalline with an average grain size in the range of 10 - 15 nm. It was found that Fe adopts bcc phase (a-Fe) with (110) as the preferred orientation along the direction of the growth. Cu layers, as expected, adopt foc phase with preferred orientation (111) perpendicular to the plane of the film. However, TEM characterization has confirmed that the first Cu layer grows initially with preferred orientation (110) and (100) textures. This study was complemented with the utilization of conversion electron Mössbauer spectroscopy (CEMS) as a local probe providing complementary information to that obtained by HXRD and HRTEM. percentage by weight of~79 % of bcc Fe phase (a-Fe), 18 % of fcc Fe phase (y-Fe) and a paramagnetic phase of 3 % were determined. The paramagnetic phase was attributed to Fe-Cu alloying at the interface region. The existence of the intermixing of Fe-Cu at the interface or interface roughness was studied by GXRD. An interfacial roughness varying from 0.6 nm to 1.2 nm depending upon the individual thickness of Cu layers was identified. Magnetic and electrical-transport properties were carried out by vibrating sample magnetometer (VSM) and four-point probe (FPP), respectively. Fe/Cu MLs were found to present a ferromagnetic (F) coupling irrespective of Cu thickness layer. This result was interpreted in terms of direct contact of Fe layers via pinholes within a Cu spacer. Electronic transport results have confirmed this assumption as the magnitude of magnetoresistance (MR) did not exceed 0.2 %. The existence of high roughness and therefore strong fluctuation of Cu spacer thickness coupled to the pinholes in the Cu layers were found to be at the origin of the dramatic reduction of MR magnitude. Correlation between magnetic and magneto-transport, and structural properties showed that the spin dependent scattering of conduction electrons, the origin of MR effect, occurs mainly at the Fe-Cu interface with island structures and/or limite Fe/Cu(100) coupled antiferromagnetically (AF.)
