Influence of additives on the structure and magnetic properties of electrodeposited magnetic film FeCoNi alloy

Journal of Chemistry, Vol. 44 (4), P. 510 - 513, 2006 INFLUENCE OF ADDITIVES ON THE STRUCTURE AND MAGNETIC PROPERTIES OF ELECTRODEPOSITED MAGNETIC FILM FeCoNi ALLOY Received 26 July 2005 MAI THANH TUNG1, BUI THI KHANH NHUNG2 Faculty of Chemical Technology, Hanoi University of Technology International Training Institution for Materials Science, Hanoi University of Technology summary Influence of additives saccharin, thioure and natrilaurylsulphate on structure and magnetic properties of electrodeposited FeCoNi alloy films was investigated using scanning electron microscope (SEM), X-ray Diffraction (XRD) and hysteresis loop measurement. SEM results showed that all films electrodeposited in solutions containing additives have fine crystall structures. The bcc/fcc intensity ratio and mean grain size size calculated from XRD analyses indicate that the grain size decreases and the bcc texture of the films increases following the sequence: non-additive, natrilaurylsulphate, saccharin and thioure. The changes of both factors mean grain size and bcc texture result a decrease of magnetic coercivity Hc following the above sequence. I - INTRODUCTION Magnetic thin films of ternary alloy FeCoNi have been widely applied for fabrication of magnetic sensors and write-read head of computers [1 - 3]. Although the FeCoNi film can change from soft to hard magnetic material depending on the composition, this type of alloy has been mainly used for substitution of soft magnetic permaloy (Ni80Fe20) owing to its higher magnetic flux density Bs and higher specific resistance [1 - 3]. Among the methods for fabrication of the magnetic thin films, electrodeposition technique is one of the most widely used processes due to its cost efficient and possibility to produce the 3D magnetic microstructures. In order to improve the magnetic, mechanical and corrosion protection properties of the electrodeposited FeCoNi thin film, several additives can be added into the deposition electrolyte. Among them saccharin, 510 thioure and natrilaurylsulphate are the most frequent used [1 - 4]. In previous works, we have shown that the additions of the saccharin, thioure and natrilaurylsulphate influence on reduction behavior of Fe2+, Co2+ and Ni2+ and thereby change the anomalous ratios during the electrodeposition process [4]. In this paper, we present results of study on the influence of additives saccharin, thioure and natrilaurylsulphate on the structure and the magnetic properties of the electrodeposited FeCoNi alloy film. II - EXPERIMENTAL Electrodeposition of FeCoNi film was performed on Cu cathode, which was shielded by epoxy resin and exhibited active surface area of 1 cm2. Prior to electrodeposition, the surface of the cathode was degreased, rinsed and activated in H2SO4 5%, subsequently. Electrodeposition was performed in a conventional 2 electrodes electrochemical cell with Pt anode. The basic deposition electrolyte (without additives) consisted of 0.01 M FeSO4, 0.05 M CoSO4, 0.2 M NiSO4, 0.4 M H3BO3, 0.3 M NH4Cl, pH was adjusted by H2SO4 to keep the value of 2.8, t = 50 C and constant current density Dc = 10 mA/cm2. All chemicals were P.A grade and made in China. In order to study influences of additives, saccharin 2 g/l, thioure 0.02 g/l and natrilaurylsulphate 0.01 g/l were added into the basic electrolyte. Surface morphology of the obtained electrodeposited films was investigated using Scanning Electron Microscopy (SEM) (JMS 5410-Jeol equipment). XRD analysis was carried out using Bucker D8 Advance apparatus. Magnetic hysteresis loop and magnetic coercivity Hc of the electrodeposited films was measured using vibrating sample magnetometer (VSM). III - RESULTS AND DISCUSSION Figure 1 shows SEM images of FeCoNi film electrodeposited in solutions without additive (Fig.1 a), with saccharin (Fig. 1b), with thioure (Fig. 1c) and with natrilaurylsulphate (Fig. 1d). The film deposited in the solution with natrilaurylsulphate has coarser crystal structure (Fig 1d). This result can be explained by the fact that natrilaurylsulphate plays a role of surfactant and retards the diffusion process only, while thioure and saccharin can react with intermediate product during the electro-deposition process [1, 5]. Therefore, the reduction of metal anions in natrilaurylsulphate occurs with higher overpotential and nucleation of metals is more difficult, leading to a coarser crystal structure. 5µm (a) non -additive 5µm (c) saccharin 5µm (b) natrilaurylsulphate 5µm (d) thioure Figure 1: SEM images of electrodeposited FeCoNi films in solutions (a) non-additive, (b) natrilaurylsulphate, (c) saccharin, (d) thioure Figure 2 shows X-ray diffraction patterns of the FeCoNi films with different additives. Results show that fcc textures (<110> and <200> orientation) and bcc (<111> orientation) 511 are observed in all deposited films, but the intensity ratio Ifcc/Ibcc is dependent on additives added into deposition solutions. Calculated intensity ratio Ifcc/Ibcc and mean grain size Lmean determined by the Sherrer’s equation of FeCoNi films with different additives is summarized in table 1. It can be seen that the content of bcc texture increases and the particle size decreases following the sequence: non-additive, natrilaurylsulphate, saccharin and thioure. 2 Figure 2: XRD pattern of electrodeposited FeCoNi films from solutions (a) non-additive, (b) natrilaurylsulphate, (c) saccharin, (d) thioure Applied field, Oe Figure 3: Hysteresis loops of FeCoNi films electrodeposited from solutions (a) non-additive, (b) natrilaurylsulphate, (c) saccharin, (d) thioure In order to study the magnetic properties of the films, hyteresis loops were recorded (Fig. 3). The magnetic coercivity Hc of films obtained from Fig. 3 are shown in Table1. It is very interesting to note the decrease of Hc also follows the sequence: Hc(non-additive) > 512 Hc(natrilaurylsulphate) > Hc(saccharin) > Hc(thioure). This result can be explained by the relation between magnetic properties and structure of electrodeposited films. The defect density of electrodeposited films decreases with decreasing of crystal size [2 - 4, 8]. Since the magnetic properties will be enhanced as defect density decreases, the finer crystal structure will result the lower Hc of` the deposited films [9]. On the other hand, the development of bcc structure, which has high magnetic orientation, also decreases Hc. Since the size of crystal decreases and the bcc content increases (table 1), Hc of the electrodeposited films decreases following the sequence: non-additive, natrilaurylsulphate, saccharin and thioure. Table 1: Intensity ratio Ifcc/Ibcc and mean grain size Lmean of FeCoNi films electrodeposited with different additives bcc/fcc intensity ratio Mean grain size Lmean, nm Magnetic coercivity Hc, Oe Non-additives 0.42 76 53 Natrilaurylsulphate 0.425 35 42 Saccharin 0.479 28 21 Thioure 0.491 22 14 (Mean grain size Lmean is determined by the Sherrer’s equation [7]: Lmean = 0.9B.cos with : wavelength, B: width of peak, : diffraction angle). IV - CONCLUSIONS The additives natrilaurylsulphate, thioure and saccharin affect the structure and the magnetic properties of electrodeposited FeCoNi films. SEM results show that the films deposited from solution containing additives have fine structure and natrilaurylsulphate results a coarser crystal comparing with saccharin and thioure. 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