Maximizing loop squareness by minimizing gradients in the microstructure

Enhanced energy product and higher operating fields can be achieved by impr oving the squareness of the demagnetization loop. In isotropic materials, i ncreasing loop squareness can be achieved by minimizing microstructural gra dients and maximizing homogeneity. Achieving homogeneity by melt spinning c an be difficult due to localized changes in cooling conditions from extrins ic factors such as gas entrapment between the melt and the chill surface an d intrinsic effects resulting from the stochastic nature of nucleation on a surface. These localized variations are reduced by altering the solidifica tion kinetics of the alloy, thus reducing its sensitivity to localized chan ges in cooling conditions. This was achieved through development of a nine- element modified Nd-Fe-B alloy which solidified with a uniform glass struct ure at much lower cooling rates. After crystallization, enhanced microstruc tural homogeneity was verified by electron microscopy and described by para meters based on the loop shape. The nine-element alloy had squarer loops an d uniformly high hard magnetic properties (>12 MG Oe) for cooling rates ove r 10 m/s. (C) 1999 American Institute of Physics. [S0021-8979(99)47708-4].