Structure and magnetic properties of Nd-Fe-B/alpha-Fe nanocomposite magnets by Co, Nb, Dy substitutions

Structure and magnetic properties of the nanocomposite magnets prepared by mechanical alloying procedure with composition 55 wt pet Nd (Fe0.92B0.08)(5 .5)+45 wt pct alpha-Fe, 55 wt pet Nd(Fe0.8-xCo0.12Nbx B-0.08)(5.5)+45 wt pe t alpha-Fe (x=0.00, 0.01, 0.03) and 55 wt pet (Nd0.9Dy0.1) (Fe0.77Co0.12Nb0 .03B0.08)(5.5)+45 wt pet alpha-Fe were studied. It was found that substitut ion of Co for Fe could significantly improve the permanent magnetic propert ies of the nanocomposite magnets and typically, the maximum magnetic energy product was increased from 104.8 kJ/m(3) (13.1 MGOe) to 141.6 kJ/m(3) (17. 7 MGOe). In contrast to the case of conventional nominally single-phase mag nets, the addition of Nb results in promoting the growth of alpha-Fe grain and is thus unfavorable for the improvement of permanent magnetic propertie s of the nanocomposites. Although the addition of Dy can increase the coerc ivity of the magnets, the increase of magnetic anisotropy of hard phase lea ds to decrease of the critical grain size of soft phase. Additionally it ca uses the difficulty of preparing the nanocomposites because it is more diff icult. to control the grain size of soft phase to meet the requirement of a ppropriate exchange coupling between hard and soft grains.