Growth of binary Ni-Fe films: Characterisations at low and high potential levels

摘要

Binary Ni-Fe films relating their magnetoresistance and magnetic properties with crystal structure and surface morphology, and the corresponding film composition were investigated at low and high deposition potentials. Based on the results obtained from a cyclic voltammetry curve, a potential region between -1.3 V and -1.8 V was selected, and the current-time transients were recorded to control the proper film growth. The Ni-Fe films were potentiostatically electrodeposited on polycrystalline titanium substrates at low (-1.3 V) and high (-1.8 V) deposition potential. The data from the energy dispersive X-ray spectrometry and the inductively coupled plasma atomic emission spectroscopy demonstrated that the Ni and Fe content in the films varied as the potential changed. The magnetotransport properties and magnetic characteristics studied by a vibrating sample magnetometer (VSM) were observed to be affected by the deposition potentials. All films were also noted to exhibit anisotropic magnetoresistance behaviour. At low potential, the magnitude of the longitudinal magnetoresistance (LMR) was high (3.93%) and that of the transverse magnetoresistance (TMR) was low (3.49%) while for the film at high potential the LMR (2.76%) and the TMR (3.66%) magnitudes were obtained. Magnetization measurements by VSM revealed that the saturation magnetization, M_s was 779 emu/cm~3 and saturation field, H_s was 142 Oe at low potential while for the films deposited at high potential the M_s and H_s were 749 emu/cm~3 and 262 Oe, respectively. However, the coercivities in the films were found to be around 4.5 Oe, regardless of the potential. Also, the magnetic easy axis was found to be in the film plane for all samples. The structural analysis of the films was carried out using the X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. To XRD analysis, all films have a strong (111) texture of face-centred cubic structure and the lattice parameters, d-spacings and average grain size slightly changed with deposition potential. The films studied by SEM revealed that they have smaller grains grown at low deposition potential compared to those deposited at high potential. The differences observed in the properties of the films might be attributed to the compositional changes caused by the deposition potential.