Co-Fe films: effect of Fe content on their properties

The characterizations of Co-Fe films electrodeposited on Ti substrates under potentiostatic conditions were investigated as a function of the Fe content in the films. The compositional analysis was carried out by energy dispersive X-ray spectroscopy. Scanning electron microscopy used to analyze the surface morphology of the films revealed that the film surface became rather smooth with the increase of the Fe contents. X-ray diffraction patterns showed that the crystal structure changed depending on the Co:Fe ratio in the films. It was observed that the crystal structure converted from the predominant face-centered-cubic to the body-centered-cubic with increasing Fe content. All films showed anisotropic magnetic resistance, but their magnitudes decrease as the Fe content increases. Magnetic data obtained from by vibrating sample magnetometer revealed that the changes observed in the saturation magnetization and coercivity values may arise from the Fe content of the films. The different magnetic and magnetotransport properties may come from the structural differences caused by the Fe content.     

Effect of electrolyte pH and Cu concentration on microstructure of electrodeposited Ni-Cu alloy films

Single Ni and Ni-Cu alloy films were electrodeposited on polycrystalline Ti substrates from electrolytes with different pH values under potentiostatic control. The deposition processes of the films were evaluated by the current-time transients recorded during deposition. The analysis of the transients clearly showed that the initial deposition of Ni is affected by the electrolyte pH, while in the Ni-Cu alloys the Cu concentration of the electrolyte is more effective than the electrolyte pH. The microstructural analysis by X-ray diffraction (XRD) indicated that the texture degree in both Ni and Ni-Cu alloy films, which have face-centered cubic (fcc) structure, changes with the electrolyte pH. The surface morphology of the samples was investigated using the scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was observed from SEM and AFM studies that the surface roughness of Ni deposits is not considerably affected by the electrolyte pH, while in Ni-Cu alloy films it changes significantly with both the electrolyte pH and the Cu concentration. Accordingly, the surface roughness of the Ni-Cu alloy films increased as electrolyte pH decreased and Cu concentration increased.     

Electrodeposition and Characterization of Co Particles on Ultrathin Polypyrrole Films

Ultrathin polypyrrole (PPy) films with the thicknesses of 20, 50, and 100 nm were prepared by electropolymerization. Co particles with a charge density in the range of 125–1,250 mC cm^?2 were grown on these ultrathin PPy films. Current time transients were used to investigate the electrochemical properties. It was observed that the deposition of Co becomes more difficult as the PPy film gets thicker. The chemical structure of PPy films in the reduced and oxidized forms and a PPy film with Co particles were examined with Fourier transform infrared spectroscopy (FTIR). The characteristic peaks of the oxidized PPy film were observed. The intensity and position of some peaks changed, and new peaks appeared for the reduced PPy film, possibly as a result of undoping of the PPy film. There are further differences in the spectrum of Co on PPy. The morphology of the films was studied by scanning electron microscopy (SEM). It was found that the morphology was affected by both the PPy film thickness and the Co charge density. Magnetic measurements were made by vibrating sample magnetometry (VSM). The magnetic moment of the samples increases with both decreasing PPy film thickness and increasing charge density due to increased Co deposition. For all samples, the easy axis is parallel to the film plane.     

Dynamic hysteresis modelling for nano-crystalline cores

This paper presents an artificial neural network approach based on dynamic Preisach model to compute hysteresis loops of nano-crystalline cores. The network has been trained by a Levenberg–Marquardt learning algorithm. The model is fast and does not require tremendous computational efforts. The results obtained by using the proposed model are in good agreement with experimental results.     

Properties of Electrodeposited CoFeNi/Cu Superlattices: The Effect of CoFeNi and Cu Layers Thicknesses

CoFeNi/Cu superlattices were grown on Ti substrate by electrodeposition as a function of the ferromagnetic and non-magnetic layer thicknesses. In order to examine the effect of the Cu layer thickness on the film properties, the Cu layer thickness was changed from 0.5 to 6 nm, while the CoFeNi layer thickness was kept constant at 4 nm. Also, for the CoFeNi layer effect, the CoFeNi layer thickness was changed from 2 to 15 nm, while the Cu layer thickness was fixed at 4 nm. The structural analysis studied by X-ray diffraction indicated that the superlattices have face-centered-cubic structure. Magnetic characteristics were investigated by vibrating sample magnetometer. From the hysteresis curves, the coercivity and the saturation magnetization were determined. It was found that the easy-axis of the films is parallel to the film plane. Magnetoresistance measurements were made by the Van der Pauw method at the room temperature with magnetic fields up to ±12 kOe. All superlattices exhibited giant magnetoresistance (GMR). As the ferromagnetic layer thickness increased up to 4 nm, the GMR value increases up to 22 % and then decreases. The superlattices saturated at the lower magnetic layers with increasing ferromagnetic layer thickness. The maximum GMR value was obtained to be 22 % for a superlattice with 375[CoFeNi(4 nm)/Cu(4 nm)].