Transformation of the crystalline and electron structures of the NdFeB alloys modified with Titanium

DEREWNICKA, D.; LEDE, E.; PAGNOLA, M.; SACCONE, F. D.; SPYRA, M.; LEONOWICZ, M.; PAMPILLO, L. G.

Nagasaki

Workshop; 22nd International Workshop on Rare-Earth Permanent Magnets and Their Applications (REPM 12); 2012

The Society of Non-Traditional Technology

This work studied alloys NdyFe(86-x-y)B14Tix (x = 0, 2, 4; y = 7, 8). The material was cast in the form of a partially amorphous ribbon which was subsequently annealed at 953K for 15 minutes. Their magnetic properties were measured using a vibrating sample magnetometer. The microstructure of alloys was investigated using high-resolution transmission electron microscopy (HR TEM) supplemented by the investigation of their chemical composition using energy dispersive X-ray spectroscopy (SEM-EDX). Detailed information on the phase constitution was obtained from the Mӧssbauer spectroscopy. XANES (X-ray Absorption Near Edge Structure) experiments were performed to measure the spectra of Nd - L III and Fe ? K edges. Enriching the alloy with titanium improves its magnetic properties. At a 4 at. % of Ti a few percent increase of magnetic remanence occurred. Coercivty was doubled and more than twofold increase of the maximum energy product was observed. The best properties were obtained for the alloy composition Nd8Fe74B14Ti4 (JHc =648kA/m, Jr=972mT, (BH)max=143kJ/m3). The magnetically hard phase Nd2Fe14B dominates in the ternary alloy (x=0). It transforms into the Nd2Fe12.6BTi1.4 phase with the addition of Ti. Titanium replaces the iron atoms in the elementary cell of the Nd2Fe14B in a continuous manner, which results in a variable content of this element in individual grains. In addition, the presence of magnetically soft phases α-Fe, Nd2Fe23B3 and Fe2B was identified as well as the paramagnetic phase Nd1.1Fe4B4. Their proportion varies depending on the percentage of the elements in the investigated alloys. The investigation of X-Ray absorption spectrum for neodymium and iron showed that in samples without Ti, there is a charge transfer from Nd to Fe while Nd concentration increases from 7 to 8 at.%. It was found that Ti addition promotes modifications of the electronic structures of Nd and Fe sub-bands. It acts by promoting/destroying the available states (which appears as enhancement/reduction of the XANES peaks). This phenomenon could explain the reinforcement of remanence and coercivity which is linked to the grain refinement and a proper phase constitution.