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

Alloys of composition Nd10.8Dy0.75Tb0.75Fe79.7−xCoxZr0.8Nb0.8Cu0.4B6.0 (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 Jr and maximum energy product (BH)max increased first and then decreased with further increasing Co content x although the intrinsic coercivity Hci decreased with increasing x. The increase in remanence polarization Jr by the substitution of Co for Fe is mainly caused by the increase in the saturation polarization Js rather than by the improvement of exchange-coupling interactions. Optimum magnetic properties with Jr=1.041 T, Hci=944.9 kA/m and (BH)max=155.1 kJ/m3 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.