Structure and magnetic properties of the nanocomposite magnets prepared by mechanical alloying procedure with composition 55 wt pct Nd (Fe0.92B0.08)5.5+45 wt pct a-Fe, 55 wt pct Nd(Fe0.8-xCo0.12Nbx B0.08)5.5+45 wt pct a-Fe (x=0.00, 0.01, 0.03) and 55 wt pct (Nd0.9Dy0.1) (Fe0.77Co0.12Nb0.03B0.08)5.5+45 wt pct a-Fe were studied. It was found that substitution of Co for Fe could significantly improve the permanent magnetic properties of the nanocomposite magnets and typically, the maximum magnetic energy product was increased from 104.8 kJ/m3 (13.1 MGOe) to 141.6 kJ/m3 (17.7 MGOe). In contrast to the case of conventional nominally single-phase magnets, the addition of Nb results in promoting the growth of a-Fe grain and is thus unfavorable for the improvement of permanent magnetic properties of the nanocomposites. Although the addition of Dy can increase the coercivity of the magnets, the increase of magnetic anisotropy of hard phase leads to decrease of the critical grain size of soft phase. Additionally it causes the difficulty of preparing the nanocomposites because it is more difficult to control the grain size of soft phase to meet the requirement of appropriate exchange coupling between hard and soft grains.
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