Li Jiang

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.

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 (Hc = 2 Oe, Ms = 1403 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.

Magnetic performance and corrosion resistance of electroless plating CoWP film

The CoWP film with good magnetic performance and corrosion resistance was electrolessly plated from alkaline solution. The technical parameters of the electroless plating system were optimized. When the pH value of electroless plating solution was 11.0 and the reducing agent (NaH2PO2) content was 0.4 mol·L−1, the target chemical reactions proceeded in the electroless plating solution smoothly with negligible interference and side effects. CoWP film prepared under optimal deposition condition contained more hexagonal close-packed (hcp) cobalt (ɛ-Co) of [110] and crystallographic orientation of Co [002]. VSM analysis reveals that the saturation magnetization of the CoWP film is 100∼220 Am2·kg−1 and coercivity is (2.87∼4.38)×104 A·cm−1. The corrosion behavior of CoWP film in 3.5% NaCl aqueous solution was studied by electrochemical experiments. The results prove that the corrosion resistance of the CoWP film deposited under the optimal deposition condition exhibites relatively lower corrosion current of (3.054∼3.162)×10−6 A·cm−2. The surface morphology analysis indicates that the film is smooth and composed of regular-shaped crystallites.

Effect of magnetic fields on pulse plating of cobalt films

Magnetic fields parallel to the electrodes were introduced during a pulse plating process to obtain cobalt thin films from alkaline baths. Effects of different magnetic intensities on the composition, microstructure, and magnetic properties of cobalt thin films were investigated. It was found that the deposition speed increased gradually with the increase of magnetic intensity. Almost all of the deposited films were crystalline and showed Co(002), Co(100) peaks. With the rise on the magnetic intensity, the intensity of Co (002) peak raised gradually. Magnetic fields would induce cobalt growing along (002) orientation. The films were densely covered with typical nodular structure. Films of smaller grain size and smooth surface could be formed under high magnetic intensity (1 T) as a result of magnetic force and MHD effects. Moreover, higher magnetic intensity induced larger saturation magnetization and lower coercivity. With the rise on magnetic intensity, cobalt contents in the films increased gradually, which led to the rise of saturation magnetization.

Magnetic performance and corrosion resistance of cobalt based magnetic films

Abstract To optimise the composition of magnetic materials applied in the fabrication of ultralarge scale integration (ULSI) devices and microelectromechanical systems (MEMS), the magnetic performance and anticorrosion property of cobalt based magnetic films (CoWP, CoPtP and CoMoP) were investigated using vibration sample magnetometer (VSM) and electrochemical technologies (potentiodynamic polarisation curve and electrochemical impedance spectroscopy). Results indicate that CoWP has a small coercivity (592·73 Oe) and large saturation magnetisation value (144·20 emu.g−1); while CoPtP and CoMoP films are hard magnetic materials with coercivity of 1786·57 and 2745·20 Oe, saturation magnetisation value of 91·72 and 120·74 emu.g−1 respectively. Electrochemical measurements reveal the order of corrosion resistance in 3·5%NaCl solution was CoPtP film>CoWP film>CoMoP film. In the fabrication of ULSI devices and MEMS, CoPtP film was recommend to be one of the most suitable magnetic materials. CoPtP film was thick with finer grains (52–78 nm) and lower roughness (18·212 nm).

Effects of Pulsed-Electrodeposition Parameters on the Property of Aluminum Film onto Sintered NdFeB Magnets

The aim of this study is to investigate the pulse-electrodeposition parameters on the property of aluminum (Al) film onto sintered neodymium-iron-boron (NdFeB) magnets at room temperature from acidic AlCl-1-ethyl-3-methylim-idazolium chloride (AlCl3-EMIC) ionic liquid (2:1 molar ratio AlCl3EMIC). The effects of pulse frequency and duty ratio on the surface morphology, particle size, thickness, hardness, deposition rate, preferred orientation of Al grains and corrosion resistance of the Al films were researched. The results show that the increase of duty ratio can promote the deposition rate, particle size and relative surface roughness of Al films; while the increase of pulse frequency can accelerate the deposition rate of Al film and reduce its particle size and relative surface roughness. The optimum Al film with a smooth surface and good corrosion performance were obtained at the condition of ip=12.5 mA/cm , r = 0.5, f = 5Hz.

Electrochemical mechanism of cobalt film electrodeposition process

Cobalt films were electrodeposited on glassy carbon surface in the experiment to study the electrochemistry mechanism. Cobalt electrodeposition process was investigated by cyclic voltammetry, chronoamperometry, polarization curves and so on. It was found that cobalt started to deposit combined with hydrogen evolution at −0.3 VSCE. Hydrogen evolution was dominated from −0.3 to −0.9 VSCE. However, with the voltages increased from −0.9 to −1.1 VSCE, cobalt deposition was predominated. Cyclic voltammetry curves with different scan rates indicated that cobalt deposition was a kind of irreversible and diffusion-controlled process. According to typical nucleation model promoted by Scharifker and Hills, the results from chronoamperometry curves verified that cobalt electrodeposition on glassy carbon belonged to three-dimensional models with instantaneous nucleation. Cobalt films were a kind of grain films with typical nodular structures because of three-dimensional instantaneous nucleation mechanism.

Electrodeposition of CoPtMo magnetic films with incorporation of phosphorus

Abstract Electrodeposition as a kind of significant electrochemical technique was used to prepare CoPtMo magnetic materials on copper substrate from an alkaline electrolyte. The influence of hypophosphite addition on the deposition process, alloy content, microstructure and magnetic properties of CoPtMo thin films was studied. The films that were prepared from the electrolytes without hypophosphite exhibited an fcc structure, with higher Pt percentage but lower coercivity. The presence of hypophosphite shifted alloy deposition to more negative potentials, limited the platinum percentage, caused higher Co content and exhibited an hcp structure. It was found that much higher coercivity of CoPtMo(P) than that of CoPtMo was mainly due to the incorporation of P at the grain boundaries.

STUDY ON PROPERTIES OF CoNi FILMS WITH Mn DOPING PREPARED BY MAGNETIC FIELDS INDUCED CODEPOSITION TECHNOLOGY

Magnetic field parallel to electric field was induced during plating process to prepare CoNiMn alloy films on copper substrate. Electrochemistry mechanism and properties of CoNiMn alloy films were investigated in this paper. Micro magnetohydrodynamic convection phenomenon caused by vertical component of current density and parallel magnetic field due to deformation of current distribution contributed directly to the improvement of cathode current and deposition rate. Cathode current of the CoNiMn plating system increased about 30% with 1T magnetic field induced. It was found that CoNiMn films electrodeposited with magnetic fields basically belonged to a kind of progressive nucleation mode. Higher magnetic intensity intended to obtain CoNiMn films with good crystal structures and highly preferred orientations. With the increase of magnetic intensities, surface morphology of CoNiMn alloy films changed from typically nodular to needle-like structures. Compared with coatings electrodeposited without magnetic field, CoNiMn alloy films prepared with magnetic fields possessed better magnetic properties. Coercivity, remanence and saturation magnetization of samples increased sharply when 1T magnetic field was induced during plating process.

CoNiMn magnetic films prepared by magnetic field induced codeposition technology

ABSTRACT Magnetic fields vertical to electric fields were applied during electrodeposition process to prepare CoNiMn magnetic thin films. Influences of different magnetic intensities on electrochemistry mechanism, nucleation, surface morphology and magnetic property of CoNiMn films were studied. Magnetohydrodynamics phenomenon caused by Lorentz forces during magnetic electrodeposition process tends to agitate the diffusion layer near cathode. It was found out that, CoNiMn films fabricated by magnetic electrodeposition process belonged to a kind of typical progressive nucleation mechanism. Anomalous codeposition phenomenon of CoNi was affected by magnetic fields. Higher magnetic intensity tended to obtain smooth surface of CoNiMn films with smaller and denser particles. Coercivity and remanence of CoNiMn alloy films increased sharply when magnetic field was induced. Magnetic property of vertical direction was better than parallel direction, which indicated that CoNiMn magnetic film possessed good vertical anisotropy.