H.L. Wang

Microstructure and magnetic properties of (Pr, Tb)2(Fe, Nb, Zr))14B/α-Fe nanocomposites

The microstructure and magnetic properties of Pr2Fe14B/α-Fe nanocomposites with small amount of Tb, Nb, and Zr additions have been investigated. A c-axis texture in the 2:14:1 phase has been observed in ribbons spun at speeds below 14 m/s. Optimal magnetic properties were found in annealed samples spun at 14–17 m/s. With small additions of Nb and Zr, the coercivity significantly increases. Nb substitution leads to a poor loop squareness, which can be significantly improved with Zr addition due to a refinement in microstructure, resulting in a drastic increase in the energy product. Optimum magnetic properties with a room temperature coercivity of 8.2 kOe, and (BH)m=20.3 MGOe have been obtained in Pr7Tb1Fe87Nb0.5Zr0.5B4 ribbons. Transmission electron microscopy on this sample revealed a much finer and homogeneous microstructure with an average grain size of 20 nm.

Multi-step crystallization evolution in nanocomposite Pr8Fe86B6 alloys

A multi-step crystallization evolution has been observed in melt-spun nanocomposite Pr8Fe86B6 alloys, resulting in drastically different magnetic properties. The ribbons spun at different wheel speeds consist of different volume fraction of an amorphous structure. Upon annealing the partially amorphous ribbons, a single transformation directly into Pr2Fe14B phase has been detected since the pre-existed 2 : 14 : 1 nanocrystallites serve as nucleation centres. However, a multiple-stage structural evolution was observed in the fully amorphous ribbons that crystallize first into metastable TbCu7-type phase and then Pr2Fe23B3 phase before they finally transform into a mixture of Pr2Fe14B and α-Fe. The microstructure in the samples with partially amorphous precursors is much homogeneous and finer with the grain size around 10–30 nm.

The improved magnetic properties in phosphorus substituted Pr–Fe–P–B nanocomposites

Phosphorus substituted (Pr,Tb)8(Fe,Nb,Zr,P)88B4 nanocomposites have been produced by melt-spinning. The effects of phosphorus substitution as well as wheel speed on the crystallization behavior and magnetic properties of the melt-spun samples have been investigated. With the substitution of phosphorus, the crystallization temperature of amorphous phase increases. The optimum wheel speed was found to be around 25 m/s for as-spun ribbons and 40 m/s for the annealed samples, both of which present excellent second quadrant hysteresis loop shapes due to the fine grain size of α-Fe which is around 20 nm. The addition of phosphorus also greatly improves the coercivity of Pr–Fe–B nanocomposites without a significant loss of saturation magnetization. A higher coercivity of 9.2 kOe in P-substituted samples was obtained as compared to 8.1 kOe in P-free samples. This is attributed to a narrower temperature span between the crystallization into TbCu7 structure and the transformation into the 2:14:1 phase caused by the...

Structural and Magnetic Properties of Chemically Synthesized FexPt100-x Nanoparticles with Controlled Particle Size and Shape

FexPt100-x nanoparticles were synthesized by thermal decomposition of iron pentacarbonyl and reduction of platinum acetylacetonate. The structural and magnetic properties of the nanoparticles with controlled particle size and shape were studied. The nanoparticles show superparamagnetic behavior. The particles also show hard magnetic properties with coercivity of more than 12 kOe after annealing. HRTEM and Mossbauer studies were carried out to investigate the microstructural development in annealed samples.

Reduction of ordering temperature in substituted FePtNi nanoparticles formed by chemical synthesis

In this paper, we used Ni substitution for Pt to reduce the transformation temperature of the FePt alloys where FePtNi nanoparticles were fabricated by chemical synthesis. M vs T data showed a blocking temperature at around 35 K, consistent with the tiny size (2-3 nm) of the particles. DSC data indicate a structural transformation from fcc to fct at a temperature about 70/spl deg/C lower in Fe/sub 60/(Pt/sub 0.7/Ni/sub 0.3/)/sub 40/ than in Fe/sub 58/Pt/sub 42/ as confirmed by XRD and hysteresis loop measurements. Mossbauer spectra and relation of coercivity with annealing temperature and time were also presented.

Effects of Co substitution on the magnetic and microstructural properties of melt-spun Pr/sub 7/Tb/sub 1/Fe/sub 87-x/Co/sub x/Nb/sub 0.5/Zr/sub 0.5/B/sub 4/ nanocomposites

In this paper, we have investigated the magnetic and microstructural properties of melt-spun Pr/sub 7/Tb/sub 1/Fe/sub 87-x/Co/sub x/Nb/sub 0.5/Zr/sub 0.5/B/sub 4/ (x=0, 10, 20, 30) nanocomposites with the aim to perform magnetic annealing experiments in fully amorphous samples.