JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS - SYMPOSIA, Vol. 1, No. 3, 2009, p. 432 - 435 Structural, magnetotransport and magnetic properties of the electrodeposited Ni-Fe films arising from electrolyte pH H. KURU a* , M. ALPER b , H. KOCKAR a a Phy. Dept., Science & Literature Faculty, Balikesir Univ., 10100 Balikesir, Turkey b Phy. Dept.,Science & Literature Faculty, Uludag Univ., Görükle, 16059, Bursa, Turkey Ni-Fe films were grown on polycrystalline titanium substrates by electrodeposition. Microstructure, magnetoresistance and magnetic properties of the films were studied as a function of the electrolyte pH. Structural characterizations by X-ray diffraction showed that all films have face centred cubic structure, but the crystal texture degree was different for the films grown at high and low pH levels. At low pH the films have a preferred (111) orientation, at high pH preferred orientation is the (220). The compositional analysis revealed that the Fe content of the films increases as the electrolyte pH decrease. It was found that all films exhibited anisotropic magnetoresistance (AMR). The AMR values of the films grown at high pH are larger compared to the films at low pH. It was observed that the saturation magnetisation increases due to the increase of the Fe content in the films and the coercivities are almost constant. The magnetic easy axis is in the film plane for all samples. The differences observed in the magnetic and magnetotransport properties of the films most probably arise from the structural and compositional changes caused by the electrolyte pH. (Received April 19, 2008; accepted May 21, 2009) Keywords: Ni-Fe films, Electrodeposition, Electrolyte pH, AMR, Magnetoresistance, XRD 1. Introduction The nickel-iron deposits have been of considerable interest for magnetic devices such as recording media and magnetoresistive sensors because of having excellent magnetic properties [1]. Single ferromagnetic films such as Ni, Fe, Co and their alloys exhibit anisotropic magnetoresistance (AMR) [2, 3]. The AMR effect has been widely studied since it was discovered by Thomson in ferromagnetic materials [4]. The effect is a relative change in resistivity between the fully magnetised and demagnetised states [5]. Most of alloys are usually produced by electrodeposition as well as vacuum systems such as sputtering and molecular beam epitaxy. Electrodeposition technique is especially interesting due to its low cost and high quality of the deposits, being extensively used to fabricate the metallic films [6,7]. The properties of the electrodeposited films are significantly affected by parameters such as the electrolyte concentration, the electrolyte pH, the deposition potentials, additives and deposition type. Among these, the electrolyte pH has a significant effect on several factors such as crystalline structure, deposit morphology and current efficiency [8]. Thus, the purpose of the present study is to investigate the structural, magnetotransport and magnetic properties of the Ni–Fe films grown on titanium (Ti) substrate at different pH levels. It was observed that the structural and magnetic properties of the films are considerably affected by the electrolyte pH. 2. Experimental The Ni-Fe films were electrodeposited from an electrolyte composed by 0.5 M nickel sulphate, 0.1 M iron sulphate and 0.2 M boric acid. After the addition of all chemicals the electrolyte pH was 3.1 and its pH value was lowered to desired values in steps by passing current through it. The current leads to the reduction of metal ions at the cathode and their replacement by hydrogen ions, lowering the electrolyte pH to the desired values [8]. Polycrystalline Ti sheets with a geometric area of 2.9 cm 2 were used as substrate and one face of each substrate was polished mechanically using emery papers of successively increasing grades, and covered with electroplating tape, except for deposition area. The uncovered area was washed in 10 % sulphuric acid and distilled water respectively. The deposition was carried out in a three electrode cell using a potentiostat /galvanostat (EGG Model 362) controlled by a computer potentiostatically. The anode was a platinum foil and saturated calomel electrode (SCE) served as the reference electrode. The films were deposited at -1.5 V with respect to the SCE at room temperature from unstirred aqueous solution. The nominal thickness of the deposits was fixed at 3 µm. After the deposition is completed, the films were mechanically peeled of their substrates and mounted on glass foil. The crystal structure of the deposits was determined by X-ray diffraction (XRD) with Cu K α radiation (0.15406 nm). For a general pattern the range recorded was 2θ = 40º–100º with step size 0.02º. The composition of films was measured by energy dispersive X-ray (EDX)