Magnetic properties and exchange interaction of rapidly quenched La or Ce substituted nanocrystalline NdFeB alloys with various compositions

The effects of La and Ce substitutions for Nd on the magnetic properties and intergranular exchange coupling of nanocrystalline (Nd1-xMx)yFe94-yB6, (M = La and Ce; y = 10 and 12; x = 0-0.4) alloys have been investigated and presented in order to improve room temperature magnetic properties and reduce the rare earth content for NdFeB based alloys. Optimum magnetic properties such as remanent magnetization Mr, maximum energy product (BH)max and coercivity Hc up to 104 emu/g, 151 kJ/m3 and 9.0 kOe have been obtained for as-quenched single phase (Nd0.95La0.05)12Fe82B alloy. The decrease in Mr for La/Ce substituted alloys is attributed to saturation magnetization reduction. An unusual increase in Hc for 5% La substituted single phase alloy is speculated to the change in microstructure and magnetic phase separation. The analysis of remanence ratio, susceptibility curve, recoil loops and Henkel plots reveal that La substituted alloys exhibit strong ferromagnetic exchange coupling between hard magnetic phases or hard and soft phases than Ce substituted alloys due to the increase of exchange length and refine microstructure by La substitution. The present results indicate that partial substitution of Nd by La or Ce leads to various change behaviors for magnetic properties and inter-grain exchange coupling.