Magnetic properties of Nd-Fe(Co, Nb)-B exchange coupling magnet

The melt spun ribbons of nanocomposite Nd9Fe85.5-xCoxNb1B4.5(x = 0 - 16) ha ve been prepared by rapid quenching and post heat treatment. The best magne tic properties obtained in Nd9Fe84.5Nb1B4.5 ribbons are as follows: (BH)(ma x) = 156 kJ/m(3),J(r) = 1.11 T and mu(0)H(cJ) = 0.68 T. It is shown that th e melt spun ribbons consist of bath 2:14:1 compound and alpha-Fe(Co, Nb) ph ases with mean grain sizes smaller than 30 nm. The effect of exchange coupl ing between the nanostructure grains of Nd-2(Fe, Co, Nb)(14)B and alpha-Fe( Co, Nb) are observed clearly. The Curie temperature enhancement is about 10 K and the largest reduced remanence achieved 0.776. It is also indicated t hat there is a close relation between the reduced remanence and the mean gr ain size of alpha-Fe phase. The smaller the mean grain size of alpha-Fe pha se, the greater the remanence enhancement. The Curie temperature of the mel t spun ribbons increases quickly with a rate of 11.3 K/at%. The coercivity, remanence and maximum energy product decrease monotonically with increasin g Co content for the Nd9Fe85.5-xCoxNb1B4.5 ribbons.