Hard Magnetic Films of Co–Ni–P

Films of Co–Ni–P with thicknesses from 0.020 to 3 μ and showing unusual magnetic properties have been prepared by electrodeposition onto polished brass substrates. The crystallite size was very small (∼100 Å); no crystallographic orientation could be detected. The coercivity, in the range 375–600 Oe, increased steeply with thickness from 0.020 to 0.1 μ, then decreased logarithmically with increasing thickness. The remanence coercivity behaved similarly. The ratio of remanent intensity to saturation intensity was high (∼0.70–0.80), the sides of the loop were almost vertical, and yet the films were completely isotropic in the film plane. This combination of properties in films of high coercivity is difficult to explain in terms of existing theories of magnetization reversal. Torque curves were measured and showed a weak sinθ dependence at fields less than the coercivity and a weak sin2θ dependence at higher fields. Graphs of rotational hysteresis W as a function of applied field had a shape which was, in general, independent of film thickness. The peak occurred at about 600 Oe and the maximum anisotropy field was ∼6500 Oe. Calculation of the rotational hysteresis integral $${\displaystyle {\int }_0^{\infty }}\frac{W}{I_s}\left(\frac{1}{H}\right)$$ gave values which ranged from 1.9 for the thin films to 4.8 for the thicker ones. Models for magnetization‐reversal processes in these films are discussed.