Superparamagnetic behavior of rapidly quenched Ni81P19 alloys

The magnetic properties of Ni81P19 metallic glass ribbons obtained by melt quenching after different heat treatments of the melt have been investigated. It has been found that all ribbons can be considered to be complex many-structure systems. Thus, an amorphous phase coexists with dispersed Ni-rich particles that in turn contain domains of pure nickel. The particles exhibit a superparamagnetic behavior. The magnetic moment of the nickel particles depends slightly on temperature and magnetic field at temperatures below 400 K. During heating to higher temperatures the particles lose their magnetic ordering and turn into a paramagnetic Ni-phase before processes involving structural relaxation and crystallization start. The amount of 'primary' Ni-phase increases substantially if the melt is overheated to 1570 K before the rapid quench.