Effects of Lanthanum on Magnetic Behavior and Hardness of Electroless Ni–Fe–P Deposits

Abstract

Abstract In this paper, the effects of lanthanum on the deposition rate, composition, structure, hardness, magnetic and anti-corrosion behaviors of electroless Ni – Fe – P deposits prepared from sulphate bath were investigated. In order to characterize the deposits, gravimetric and electrochemical measurement, scanning electron microscopy, X-ray diffraction, and magnetic measurement were applied. The results show that the deposition rate decreases with increasing LaCl3 · 7 H2O concentration in the bath due to the competition adsorptions between rare earth lanthanum, metal ions, and hypophosphite on the surface of the substrate. The magnetic behavior of the deposit is strongly dependent on the LaCl3 · 7 H2O concentration in the bath. The coercive force of the deposit increases, while its saturation magnetization decreases with LaCl3 · 7 H2O concentration increase. When the LaCl3 · 7 H2O concentration reaches 1.50 g l – 1, the deposit shows a rectangular hysteresis loop with high coercivity. The moderate addition of lanthanum in the bath will increase the hardness of the deposits as a result of the change of composition and structure of deposits. However, the addition of lanthanum has little effect on the corrosion resistance of the deposits.