Crystallization, morphology and magnetic properties of melt-spun (Nd,Pr,Dy)/sub 2/(Fe,Co,Mo)/sub 14/B//spl alpha/-Fe nanocomposites
Crystallization, phase evolution, nanostructure, exchange coupling, and hard magnetic properties of melt-spun Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 85/B/sub 6/ and Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 78/Co/sub 6/Mo/sub 1/B/sub 6/ nanocomposites have been studied. All the Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 85/B/sub 6/ alloys annealed for 30 s at 565/spl deg/C or above contain nanostructured /spl alpha/-Fe and Nd/sub 2/Fe/sub 14/B-type (2:14:1) phases, whereas Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 78/Co/sub 6/Mo/sub 1/B/sub 6/ alloys annealed at 600/spl deg/C or below are mainly composed of /spl alpha/-Fe and a metastable 1:7 phase. A small amount of 2:14:1 phase forms after annealing at 600/spl deg/C. When annealed at 640/spl deg/C or above, the hard phase in Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 78/Co/sub 6/Mo/sub 1/B/sub 6/ alloys is the 2:14:1 phase rather than the 1:7 phase. The differences in magnetic properties of the Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 85/B/sub 6/ and Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 78/Co/sub 6/Mo/sub 1/B/sub 6/ nanocomposites at different anneal temperatures result from the different nanostructures, exchange coupling and phase components present in the alloys, in particular from the different amount of the 1:7 phase.
Effects of quenching rate on the phase transformation and magnetic properties of melt-spun Pr8Fe86B6 ribbons during annealing
Abstract Phase transformations and magnetic properties of overquenched Pr 8 Fe 86 B 6 ribbons during annealing treatment have been investigated. The as-quenched structure of the ribbons was varied by changing the quenching rate during the melt spinning process. It was found that, depending on their as-quenched structures, the phase transformations of the ribbons during annealing may take place in one of the following sequences: (1) Amorphous phase (Am)+Pr 2 Fe 14 B+α-Fe→Pr 2 Fe 14 B+α-Fe; (2) Am+α-Fe→ Am′+α-Fe→α-Fe+Pr 2 Fe 23 B 3+ Pr 2 Fe 14 B→Pr 2 Fe 14 B+α-Fe; and (3) Am→Am′+α-Fe→Pr 2 Fe 23 B 3 +α-Fe→ Pr 2 Fe 14 B+α-Fe. However, for all the ribbons, the microstructure after optimal annealing was found to consist only of two magnetic phases: Pr 2 Fe 14 B and α-Fe. The optimum magnetic properties (intrinsic coercivity H ci and remanent polarization J r ), and the squareness of the demagnetization curves of the annealed ribbons deteriorated drastically with increasing quenching rate of unannealed precursors. This deterioration can be attributed to the formation of a coarser and more irregular microstructure during annealing of the samples initially melt spun with higher wheel speeds, which was confirmed by our TEM observations, analysis of the temperature dependence of coercivity and measurement of irreversible susceptibility.
Overlayer-induced anisotropic alignment of Nd2Fe14B nanograins
Highly anisotropic Nd2Fe14B thin film has been produced by triggering crystallization of sputter-deposited amorphous Nd–Fe–B layer by deposition of crystalline Cr overlayer. A downward growth of strongly textured Nd2Fe14B columnar grains was observed, starting from the interface between the Nd–Fe–B amorphous layer and the Cr overlayer. Cross-sectional transmission electron microscope observation results suggest that the possible mechanism of this peculiar crystallization is the heterogeneous nucleation at the surface of Nd–Fe–B amorphous layer, triggered by the crystalline Cr overlayer.