Precipitation in a Beta-Brass-Fe Alloy

Abstract

Single crystal samples of beta‐brass containing 0.1% iron were annealed at 300°C and 400°C in order to develop the iron precipitate particles. At intervals during the anneals, magnetic data were obtained and analyzed in terms of the size, shape, orientation, and general magnetic behavior of the precipitate particles. During the earliest annealing stages, superparamagnetic behavior was observed, and particle diameters were calculated from the Langevin relation. On continued annealing the magnetic properties indicated the presence of mixtures of superparamagnetic and single domain particles, and subsequently mixtures of single domain and multidomain particles. Torque curves showed that the particles were single crystals, with iron‐like magnetocrystalline anisotropy, oriented with the same crystal habit as the matrix. Single domain behavior was first observed when the particle diameters were of the order of 200 A. Elongation of the particles in the 〈111〉 directions and rotational hysteresis were noted when single domain behavior appeared. The magnetocrystalline anisotropy coefficients calculated from the torque data were reasonably close to those of iron. Maximum remanence was reached before maximum coercive force due to the much larger initial susceptibility of the superparamagnetic as compared to the multidomain particles. This was confirmed by the shapes of the hysteresis loops for the various cases.