Magnetic and structural properties of rapidly quenched Nd-Fe-Co-Ge-B alloys

We have studied the structure and magnetic properties of some rapidly quenched and subsequently annealed alloys prepared by centrifugal method with a composition (in wt %) Nd(29.5), Co( 6), B(1.1), Ge (x), Fe( balance) with x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 ( wt %) for Ge. Based on X-ray diffraction (XRD),elastic neutron diffraction, and small-angle neutron scattering ( SANS), the formation of partially crystallized main hard magnetic 2: 14: 1 ( F) phase in the amorphous matrix was detected for all as-spun samples. The size of the clusters formed for the sample with 1 wt % Ge determined based on SANS profiles was about 10 nm. It was shown that the addition of Ge shifts the maximum crystallization peak of the main 2: 14: 1 phase to higher temperatures. The variation of the magnitudes of different magnetic parameters such as H-i(c) and M-s versus Ge concentration for as-spun samples can be possibly related to the different rate of crystallization of the 2: 14: 1 phase formed. Further, for the samples doped with 0.8 and 1.0 wt % Ge and annealed at 760 C for 5 min the formation of some extra phases such as Nd5Ge3, NdFe2, NdB4, as well as a - Fe was detected by XRD. The magnetic measurements carried out using a vibrating-sample magnetometer (VSM) for these samples also supported the XRD data obtained. While the highest values of coercivity H-i(c) = 772 kA/m were obtained for the annealed samples without Ge, the highest value of sigma(r) = 69 emu/g was also obtained for the samples substituted with 0.8 wt % Ge without an appreciable reduction in iHc.