Effect of Annealing Temperature on the Coercivity and the Electrical Resistivity of the Electroplated Ni-Fe-W Alloy Film
Authors: Mundotiya Brij Mohan , Rissing Lutz , Wurz Marc Christopher 
Published: February 2020

Introduction

                Interests in the Ni-Fe-W alloys are increasing rapidly in recent years, due to outstanding mechanical, tribological, and magnetic properties as well as improved corrosion resistance [1-3]. There are a few documentations on electroplating parameters influence on the structure and the magnetic properties of plating Ni-Fe-W alloys [4-6].

In this presented work, this study addresses the preparation of Ni-Fe-W alloys by an electroplating technique. Annealing is employed to the plated alloy to enhance the magnetic and electrical properties. We investigate the influence of annealing temperature on the coercivity (HC) and resistivity of the plated alloy.

Experimental

The 80Ni-17Fe-3W alloy films are produced on Si-wafer by electroplating technique. The electrolyte is prepared by dissolving 0.150 mol/l nickel sulfate, 0.013 mol/l ferrous sulfate, 0.001 mol/l sodium tungstate, 0.040 mol/l ammonium H-citrate, 0.050 mol/l citric acid, 0.1 mol/l boric acid, and 0.05 mol/l saccharin. Deposition is carried out at a substrate temperature of 5 ºC using current density of 5 mA/cm2at constant pH 8. The deposition time is 30 minutes. Electrolyte is agitated with a paddle cell during plating. To study the effect of annealing temperature on the coercivity and electrical resistance of the plated alloy films, the plated alloy films are annealed at different temperature values of 200, 300, 400, and 500 ºC for 60 minutes in vacuum furnace.

Composition of the deposit is determined by the energy dispersive X-ray spectroscopy (EDX) technique using the scanning electron microscope (SEM). HCand electrical resistivity are inspected with the help of a BH Looper and four-point probe techniques, respectively.

Results and discussion

The change in HC and electrical resistivity of plated alloy at different annealing temperatures is shown in Fig. 1. It is observed that the HC increases from 240 ± 20 to 383 ± 28 A/m, while resistivity decrease from 32 ± 058 to 25 ± 0.19 µohm-cm with an increase in annealing temperature. This suggests that an increasing in the annealing temperature lead to grain growth and lower dislocation density [7]. The HC of the plated film depends on the grain size. At lower grain size, the alloy films consist of a large number of single domains and the intergranular arrangement of nanocrystalline grain is disordered [7]. Therefore, the ferromagnetic exchange coupling is weak and has a large disordered magnetic anisotropy between the single domains, which leads to lower HC[8-9].

The resistivity decreases with the grain size growth due to the decreasing the grain boundary volume [10-12]. Therefore, the scattering of electrons from the grain boundaries is low, resulting low resistivity.

Conclusion

The annealing heat treatment increases the coercivity and decreases the electrical resistivity of the plated 80Ni-17Fe-3W alloy film.

Acknowledgements

This work is supported by the Hannover School for Nanotechnology grant.

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Figure 1