Application of the Stoner–Wohlfarth model with interaction for the determination of the saturation magnetisation, anisotropy field, and mean field interaction in bulk amorphous ferromagnets

Magnetic hysteresis curves of bulk amorphous ferromagnet alloys of composition Nd60Fe30Al10, Nd60Fe20Co10Al10 and Pr58Fe24Al18 have been measured in applied magnetic fields up to 9 T at temperatures in the range 10–350 K. The behaviour of the demagnetisation curve in the first quadrant is interpreted using a mean field interaction model as proposed by Callen et al. [Phys. Rev. B 16 (1977) 263], which extends the Stoner–Wohlfarth model [Philos. Trans. Roy. Soc. A 240 (1948) 599] for a random distribution of non-interacting uniaxial grains. Application of the mean field interaction model enables the determination of the saturation magnetisation Ms, anisotropy field Ha, and interaction parameter d, and from these other magnetic parameters, such as the anisotropy constant, K, are deduced. For the three alloys, the temperature dependent behaviour of Ms, Ha, d and K over the range 20–350 K are found to be qualitatively similar, though there are quantitative differences. In all cases Ms increases with decreasing temperature, both Ha and K increase with decreasing temperature, reaching a peak in the range 75–120 K, and then decreasing, and d decreases approximately linearly as the temperature decreases. The physical mechanisms responsible for coercivity in these materials are discussed in the context of random anisotropy and a strong pinning model of domain walls.

► Magnetic hysteresis curves in bulk amorphous ferromagnets have been measured in fields up to 9 T from 10 to 350 K.
► The behaviour of the demagnetisation curve in the first quadrant is interpreted using a mean field interaction model.
► The mean field interaction model is an extension of the Stoner–Wohlfarth model.
► Application of the mean field interaction model enables determination of the anisotropy constant.
► Physical mechanisms responsible for coercivity are discussed in context of random anisotropy and pinning of domain walls.