Approach to magnetic saturation in nanocrystalline and amorphous Fe73.5Cu1Nb3Si13.5B9

The extremely soft magnetic amorphous and nanocrystalline Fe73.5Cu1Nb3Si13.5B9 alloy is studied with the method of approach to ferromagnetic saturation. From the magnetization curves measured in a field range up to mu(0)H = 7 T and in the temperature range 5 K < T < 300 K the following information on the microstructure and the ferromagnetic properties are obtained: (1) The spinwave stiffness constant D-Sp as determined from the paraeffect and Bloch's T-3/2 law: D-Sp = 1.41 mev(nm)(2). (2) Because of magnetoelastic interactions between stress fields and the spin system the magnetization curve in the field range mu(0)H< 1 T in the amorphous as well as the nanocrystalline material is determined by elastic dipole-like defects, In the unrelaxed amorphous state (as-quenched) the influence of long-range internal stresses is also detected. (3) In the field range mu(0)H > 1 T the susceptibility is too high to be explained exclusively by the paraeffect or the Pauli paramagnetism. The large high-field susceptibility is attributed to antiparallel coupled spins and analyzed within the framework of a two-phase-two-sublattice model.