The influence of milling and annealing conditions on the structural and magnetic behavior of Nd2Fe14B/α-Fe hard/soft magnetic nanocomposites

Abstract (Nd,Dy) 2 Fe 14 B +  x wt% Fe ( x  = 10 and 22) nanocomposite magnetic powders are synthesized by mechanical milling and annealing. This paper resumes our studies on the influence of structure and microstructure on the magnetic properties of Nd 2 Fe 14 B/α-Fe exchange coupled hard/soft magnetic nanocomposites obtained by mechanical milling and annealing. Different microstructures are obtained by changing milling conditions. In order to recover the crystallinity of the hard magnetic phase and hinder the increase of the crystallite size of Fe, two types of annealing are performed after milling. The first one, a common heat treatment, is carried out at moderate temperatures between 450 and 650 °C for 1.5 h. The second one, short time annealing, is performed at much higher temperatures between 700 and 800 °C for up to 3 min. The structure and microstructure were studied by X-ray diffraction. The morphology and chemical homogeneity of the obtained powders are checked by Scanning Electron Microscopy and Energy Dispersive X-ray measurements. The magnetic behavior is checked from hysteresis curves and the field derivative of the magnetization curve ( dM/dH vs. H plots).