H L Ge

Effects of pH values on electroless deposition of CoP films

Abstract CoP thin films were prepared on copper substrates from an alkaline bath by electroless deposition. Influences of pH values on deposition rates, compositions, structures, surface morphologies and magnetic performances of films were studied. Higher pH values could improve deposition rates and cobalt contents in the films. However, when the pH value is higher than 10, hydroxide depositions can result in the decrease of deposition rates and cobalt contents. Films prepared with different pH values show dissimilar surface morphologies. The films are densely covered with typical nodular structures when the pH value is equal to 10. However, films obtained with pHu200a=u200a11 show agglomerate and rough structures. Phosphorus in the films would help to increase coercivity.

Influence of magnetic fields on cobalt electrodeposition

Abstract Magnetic fields parallel to electrodes were introduced during plating process to prepare cobalt films from baths without additives. Effects of magnetic intensities on the nucleation process, electrochemical mechanism and surface morphology were investigated. It was found that limiting current and deposition mass increased gradually with the rise in magnetic intensities. Magnetohydrodynamic phenomenon (magnetic fields can induce currents in a moving conductive fluid, which in turn creates forces on the fluid and also changes the magnetic field itself) caused by Lorentz forces could agitate to decrease thickness of diffusion layers, which contribute to the increase in deposition rate. Reduction of cobalt on copper substrates without magnetic fields showed instantaneous nucleation process. However, cobalt reduction with 1 T magnetic intensity deviated from instantaneous nucleation process as a result of micromagnetohydrodynamic (micro-MHD) flows. Films of smaller grain size and compact surface could be obtained under 1 T magnetic intensity as a result of MHD effects.

Effect of temperatures on electrodeposition of CoWP films

Abstract CoWP alloy films were prepared by a typical citrate system electrodeposition on a copper substrate. The paper investigated effects of different temperatures on codeposition mechanism, magnetic property, component and structure of CoWP alloy films during the electrodeposition process. With the increase in temperatures, deposition rate and thickness rose gradually during the electrodeposition process. It was found that higher temperature improved contents of phosphorus and tungsten but reduced amounts of cobalt in the films. Almost all the deposited films were crystalline and formed tetrahedral structures Co3W with preferred crystallographic orientation (200) and (201). Films of dissimilar surface morphology could be observed under different temperatures. Lower saturation magnetisation and higher coercivity of CoWP films could be obtained at higher temperatures.

Preparation of NiFe films by magnetic electroplating

Abstract NiFe alloy films were prepared by magnetic electrodeposition method to replace conventional sputtering on a copper substrate. The effects of different magnetic intensities on current efficiency, throwing power and magnetic properties were investigated. Magnetic intensity played a significant role in current efficiency. When the magnetic intensity ranged from 0 to 1·0 T, the current efficiency increased from 68 to 87%. The magnetic field applied during the NiFe electroplating process would destroy the hydration state of ions in aqueous solution to increase the bath conductivity, which induced optimal throwing power. Almost all the deposited films were crystalline and formed peaks of FeNi3 (111), FeNi3 (200) and FeNi3 (220). With the rise on magnetic intensity, the intensity of all three FeNi3 peaks started to increase gradually, which induced greater crystalline. High magnetic intensity could help to obtain a smooth surface of NiFe films with small and dense particles. When the magnetic intensity ranged from 0 to 1 T, the saturation magnetisation of NiFe increased from 76 to 106 A m2 kg−1. However, the largest coercivity (7722 A m−1) could be achieved when the magnetic intensity is equal to 0·4 T.

Study on preparation of NiFeP films by pulse electrodeposition

Abstract Ultrasonic was introduced during pulse plating process to prepare NiFeP alloy films. Effects of different duty ratios and ultrasonic powers on composition, microstructure and magnetic properties of films were investigated. With the rise in duty ratios, the amount of nickel increased gradually. Higher ultrasonic power could result in larger contents of iron in NiFeP alloy films. That was because nickel reduction was potential controlled while iron reduction was diffusion controlled during the pulse plating process. Almost all the deposited films were crystalline and formed peaks of FeNi3 (111), FeNi3 (200) and FeNi3 (220). With the increase in duty ratios, the intensity of all three peaks started to decline, which led to worse crystalline and bigger grain sizes. Dissimilar surface morphology could be detected by the condition of different duty ratios and ultrasonic powers. NiFeP films with smaller grain size and smooth surface could be obtained when a higher power of ultrasonic was introduced during the pulse plating process. However, the films with rough and agglomerate nodular structures would be observed with higher duty ratios. Vibration sample magnetometer results showed that the coercivity of NiFeP films ranged from 30 to 150 Oe.

Co–W films prepared from electroplating baths with different complexing agents

Abstract The influence of different complexing agents with hydroxycarboxylic acid group on the electrodeposited Co–W thin films has been investigated. Comparison between the polarisation curves shows that the negative shift on the electrodeposition potential increased in the following order: no complexing agent, tartrate, malate, gluconate and citrate. The particular shapes of the j–t transients indicate that a nucleation and growth process was involved for the Co–W electrodeposition in the presence of complexing agents investigated. The reduced current transients follow the instantaneous nucleation model for all four complexing agents at the initial stages. Surface morphology, phase composition and magnetic properties were observed by means of field emission SEM, X-ray diffraction and vibrating sample magnetometer respectively. It has been found out that surface morphology and phase composition were markedly affected by the nature of the complexing agents. In the absence of complexing agents and in the presence of citrate, reflections of Co7W6, Co (1 0 0) and Co (0 0 2) appeared simultaneously. For the deposits obtained from solutions containing malate, there are two main peaks: Co7W6 and Co (0 0 2). In the case of tartrate, two peaks of Co are observed: Co (0 0 2) and Co (1 0 0). Reflections of Co (0 0 2) appeared for the deposits prepared from gluconate baths. Co–W magnetic thin films presented good soft magnetic properties (Hcu200a=u200a2 Oe, Msu200a=u200a1403 emu cm−3) compared with pure cobalt thin films (1370 emu cm−3) when 0··3 mol L−1 citrate was used as complexing agent.

PREPARATION OF Co–W–P MAGNETIC THIN FILMS BY ELECTROLESS DEPOSITION

An alkaline bath was developed for electroless deposition of Co–W–P thin films on a copper substrate. Effects of pH values, various concentrations of reducing agent, and different powers of ultrasonic on composition, microstructure, and magnetic properties of the films were investigated. It was found out that higher pH could improve cobalt atomic percentage and reduce amounts of phosphorus and tungsten in the film while larger amounts of NaH2PO2 would decrease the cobalt content but increase the tungsten and phosphors content. The ultrasonic was introduced during the electroless deposition. Few effects of ultrasonic on the cobalt content were observed. X-ray diffraction showed that almost all of the deposited films were crystalline and contained hexagonal cobalt with a preferred crystallographic orientation (002). However, a typical amorphous Co–W–P film, which has smooth surface, and no crystallite with definite grains could be obtained when the concentration of NaH2PO2 in the bath was over 1.2 mol/L. The films with rougher and agglomerate nodular structures would be formed in the bath with a higher pH value. Certain power (60 W, 40 kHz) of ultrasonic could smash the grains and led to the formation of a denser and smoother surface. Cracks appeared at the surface of the film when the ultrasonic power was 150 W. Vibration sample magnetometer results showed that the film with maximum magnetization (600 emu/g) and coercivity (1000 Oe) could be achieved when introducing ultrasonic (60 W, 40 kHz) during the deposition.

Study on preparation of NiFe films by galvanostatic electrodeposition

Abstract NiFe alloy films were prepared by galvanostatic electrodeposition method on a copper substrate under various deposition temperature and current density. The structure and surface morphology of electrodeposited NiFe films were analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Vibrating sample magnetometer and electrochemical workstation was used to obtain the magnetic and corrosion behaviours of the NiFe thin film. The results showed that the NiFe particle size was ranging from 10 to 30 nm. The main phase of NiFe thin films was fcc (FeNi3) structure. NiFe thin films prepared under the condition of temperature (60°C) and current density (167 A m−2) possessed low coercivity (0·18 kA m−1) and high specific saturation magnetisation (253 Am2 kg−1).

CoPtW thin films prepared by magnetic electroplating

Abstract CoPtW alloy films were prepared by magnetic electrodeposition method to replace conventional sputtering on copper substrate. The effects of different H2PtCl6 concentrations and magnetic intensities on the composition, microstructure and magnetic properties of CoPtW alloy films were investigated. With the increasing H2PtCl6 concentration, the amounts of Pt in CoPtW films increased dramatically, but the contents of both Co and W reduced gradually. Almost all of the deposited films were crystalline and contained CoPt(111), CoPt(002) and Co(002) peaks. The strongest perpendicular magnetic anisotropy could be observed when the H2PtCl6 concentration was up to 0·02 mol L−1. A higher H2PtCl6 concentration would result in bigger and agglomerate nodular structures with lots of pores. The magnetic field parallel to the electrodes during the electrodeposition process could improve the deposition rate and increase the amounts of Co in CoPtW alloy films. Magnetic fields would induce cobalt growing along the (002) orientation. Films of smaller grain size and smooth surface could be formed under high magnetic intensity (0·8 T) as a result of magnetic force and magnetohydrodynamic effects. Moreover, a transition process from hard magnetism to soft magnetism could be observed when the magnetic intensity increased from 0 to 0·8 T.

Preparation of Co–W–P alloy films by pulse plating

Abstract Co–W–P films were prepared by a pulse plating method on a copper substrate. Effects of different duty ratios on composition, microstructure and magnetic properties of films were investigated. With the increase in duty ratios, the deposition speed increased gradually during the pulse plating process. It was found that the higher ratio duty could improve contents of cobalt and reduce amounts of phosphorus in the film. Almost all the deposited films were crystalline and formed tetrahedral structures Co3W with preferred crystallographic orientation (200) and (201). Dissimilar surface morphology could be detected under different duty ratios. Atomic force microscopy showed that lower duty ratios could form typical nodular structures and the dense surface. However, the films with rough and agglomerate nodular structures would be detected with higher duty ratios. Vibration sample magnetometer results showed that higher duty ratio induced larger saturation magnetisation and lower coercivity of Co–W–P films.