Synthesis of melt-spun rare-earth transition-metal intermetallics with Nd3(Fe,Ti)29 structure (abstract)

Single phase ingots of Nd3Fe27.5Ti1.5 were prepared by argon arc melting followed by annealing at 1373 K for 72 h in evacuated sealed quartz tubes and water quenching. Pieces of the ingots were then made into ribbons using the spin-melting technique in argon atmosphere with velocities between 20-40 m/s. The ribbon samples were annealed over a range of temperatures 723-1323 K for times in the range 15-50 min. The as-spun ribbons were found to be amorphous and presented a composition close to the nominal one. After annealing, the samples were crystallized and presented the Nd3(Fe,Ti)29-type structure. From the relative intensities of the diffraction peaks it was concluded that the annealed samples presented texture. This was confirmed from the x-ray diffraction patterns of annealed ribbons after powdering which were similar to those of the bulk samples. The lattice parameters are: a = 10.63(4) Å, b=8.57(4) Å, c=9.729(5) Å and ?=97.01(2)°. Rietveld analysis on the annealed ribbons gave a composition of 60% Nd3(Fe,Ti)29, 21% Nd(Fe,Ti)12, and 19% ?-Fe. Thermomagnetic analysis curves of the as-spun ribbons showed a broad transition between 373-433 K and a secondary one at about 553 K indicating the presence of a 1:12 impurity. After annealing, the samples presented a Curie temperature typical for the Nd3(Fe,T)29 compound, 437 K and two secondary magnetic transitions characteristic for the 1:12 and ?-Fe phases, respectively. The room temperature saturation magnetization, Ms, was 145.0 and 138.7 emu/g before and after annealing, respectively. Scanning electron microscopy photographs of the annealed ribbons showed a grain size <1 ?m and the microanalysis of the grains gave a mean stoichiometry Nd3Fe24Ti5 for the 3:29 phase. The coercivity of the annealed samples was 1 kOe at room temperature. This relative low value was attributed to the presence of the soft ?-Fe impurity