Structural and magnetic properties of Nd2Fe17-delta Ga delta (delta <= 2)

Magnetization measurements of Nd2Fe17-deltaGadelta (delta=0-2) show that th e saturation magnetization, M-s, decreases with an increase in Ga content f rom 40.4 mu(B)/f.u. for Nd2Fe17 to 36.1 mu(B)/f.u. for Nd2Fe15Ga2 at 4.2 K. Neutron diffraction data at 25 K show that the magnetic moment of Fe depen ds on its crystallographic site and decreases in the order Fe(6c)> Fe(18f)g reater than or equal to Fe(18h)greater than or equal to Fe(9d). The magneti c moments of Fe(9d), Fe(18f), and Fe(18h) are found to be practically indep endent of the Ga content. However, the magnetic moment of Fe(6c) decreases from 2.81(9) mu(B) in Nd2Fe17 to 2.14(9) mu(B) in Nd2Fe15Ga2. The decrease of the Fe(6c) moment clearly reduces the exchange interaction between Fe(6c )-Fe(6c) dumbbell pairs which explains the decrease in the anomalous therma l expansion with an increase in Ga concentration. The reduced Fe(6c)-Fe(6c) exchange interaction may also play an important role in increasing the Cur ie temperature, T-C, with Ga content; T-C increases from 327 K in Nd2Fe17 t o 535 K in Nd2Fe15Ga2. (C) 2000 American Institute of Physics. [S0021-8979( 00)22008-2].