Exchange interactions and magnetization reversal of nanocrystalline (NdDyTb)_(12.3)(FeZrNbCu)_(81.7)B_(6.0) ribbons with Co substitution

摘要

Alloys of composition Nd_(10.8)Dy_(0.75)Tb_(0.75)Fe_(79.7-x)Co_xZr_(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.