Exchange interactions and magnetization reversal of nanocrystalline (NdDyTb)12.3(FeZrNbCu)81.7B6.0 ribbons with Co substitution

Abstract Alloys of composition Nd 10.8 Dy 0.75 Tb 0.75 Fe 79.7− x Co x Zr 0.8 Nb 0.8 Cu 0.4 B 6.0 ( x =0, 3, 6, 9, 12, 15) were prepared by melt spinning at 22 m/s and subsequent annealing. Phase analysis revealed single-phase materials. Magnetic structure and remanence analysis indicated strong exchange coupling between neighboring grains in all samples. The remanence polarization J r and maximum energy product ( BH ) max increased first and then decreased with further increasing Co content x although the intrinsic coercivity H ci decreased with increasing x . The increase in remanence polarization J r by the substitution of Co for Fe is mainly caused by the increase in the saturation polarization J s rather than by the improvement of exchange-coupling interactions. Optimum magnetic properties with J r =1.041 T, H ci =944.9 kA/m and ( BH ) max =155.1 kJ/m 3 were achieved for x =12 ribbons. The mechanism of magnetic hardening in all samples was of pinning type by analyzing initial magnetization and the dependence on applied magnetizing field of the coercivity and remanence.