Magnetism of ordered and disordered alloys of R(2)Fe(14)B (R = Nd, Er) type

Magnetic susceptibility, magnetization and neutron diffraction measurements have been performed to study structure and magnetic states of crystalline and amorphous Nd(2)Fe(14)B and Er(2)Fe(14)B alloys. In the crystalline state there exists a large (about 20%) anisotropy of Er-sublattice magnetization. Values of the magnetic anisotropy constant of Er ions and the Er-Fe exchange-coupling parameter were estimated using temperature dependence of the Er- and Fe-sublattice magnetizations. Amorphous state of the samples was obtained by irradiation of fast (E(eff) (greater-than or equal to) 1 MeV) neutrons with a fluence up to the 1.2 x 10(20) n/cm(-2) at 340 K. It is shown that antiferromagnetic coupling between the rare-earth and iron spins is kept in the amorphous state. Amorphization of the samples is found to result in reduction of the Curie temperature (T(C)) by about 200 K and almost total absence of coercivity. We suggest that the strong decrease of T(C) is a consequence of enhancement of negative Fe-Fe interactions as a result of dispersion of interatomic distances, which is a characteristic feature of the amorphous state.