Magnetic and Structural Properties of Rapidly Quenched Nd-Fe-Co-Ge-B Alloys

摘要

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 percent) Nd(29.5), Co(6), B(l. 1), Ge (x), Fe(balance) with x = 0.0, 0.2,0.4,0.6,0.8,1.0 (wt percent) 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 (PHI) phase in the amorphous matrix was detected for all as-spun samples. The size of the clusters formed for the sample with 1 wt percent 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 _iH_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 percent Ge and annealed at 760 deg C for 5 min the formation of some extra phases such as Nd_5Ge_3, NdFe_2, NdB_4, as well as alpha-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 _iH_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 percent Ge without an appreciable reduction in _iH_c.