The Influence of Residual Stress on the Magnetic Characteristics of Electrodeposited Nickel and Cobalt

Cobalt and nickel were electrodeposited from aqueous solutions at a current density of 16 ma/cm 2 . The influence of the metal chloride salt and saccharin concentrations on the residual stress and microstructure of the cobalt and nickel electrodeposits was investigated in conjunction with measurements of their magnetic characteristics. In all cases the residual stress in the deposits as measured with a stressometer was found to be tensile in nature, i.e., the deposits tend to contract. The coercive force of the cobalt and nickel deposits was determined as a function of the residual or internal stress at a thickness of approximately 7μ. This coercive force was compared with a theoretical coercive force obtained from the relation Hc = σ λ / Is as proposed by Kersten where σ is the experimentally determined internal stress, λ is the magnetostriction value, and Is is the saturation magnetization. It is shown that the coercive force of nickel deposits is directly proportional to the internal stress. However, the coercive force of cobalt deposits appears to be dependent on the crystal structure as well as the internal stress. Heat treatment of the cobalt deposits for 2 hr at 440 °C in nitrogen results in a decrease in the squareness and an increase in the coercive force while nickel deposits increased in squareness and decreased in coercive force. The former results are explained on a crystal structure basis while the latter results can be explained on a stress relief basis.