Structural and magnetic characterization of the Nd2Fe14B + 10%wt.Fe system subjected to high-energy milling

Abstract

We have investigated exchange-spring magnets made from powders prepared by high-energy milling Nd2Fe14B mixed with 10%wt. Fe, milled for 6 h in a planetary mill, varying the rotation velocity and the starting grain refinement of the soft phase. The samples were characterized by X-ray diffraction, magnetization techniques and 57Fe Mossbauer spectroscopy. The diffractometric and Mossbauer analyses revealed that the Nd2Fe14B compound was partially decomposed in the milling process, increasing the amount of free iron and reducing the grain size of both. Indicative for the Fe2B and Nd1-eFe4B4 phase separation was also found. The magnetization versus applied magnetic field curves showed that both the remanence and coercive field for the 500 rpm milled samples reached values higher than those earlier obtained for un-milled or similarly milled single Nd2Fe14B. However, milling with 600 rpm showed to be deleterious to the same magnetic parameters. It was also demonstrated that milling using iron with less refined grains is more effective to improve the magnetic properties of the composite system.