Coercivity extrema in melt-spun CuCo ribbons: Effects of the magnetic moment distribution

Measurements of magnetization loops on melt-spun CuCo ribbons revealed a mi nimum in the temperature dependence of the coercivity. A coherent interpret ation was given through Monte Carlo simulations of a dispersed system of no ninteracting, uniaxial magnetic granules embedded in a nonmagnetic matrix. The coercivity is implicitly defined by the balance between the negative ma gnetization of superparamagnetic granules and the remaining magnetization o f blocked granules after saturation in the positive field direction. When t he temperature rises in a system made of a large amount of small granules a nd a small amount of big granules, unblocking predominates over thermal flu ctuations and the coercivity decreases until a certain temperature at which most of the small granules are superparamagnetic; above this temperature, thermal fluctuations predominate, and the coercivity increases almost linea rly with the temperature until the final unblocking of the big granules. (C ) 1999 American Institute of Physics. [S0021-8979(99)04618-6].