We have investigated effects of an external magnetic field in the impurity
Anderson model with a finite on-site Coulomb repulsion U. Large Nf
expansion is employed in the slave boson representation, by taking into account
f0, f1, and f2 subspaces. To evaluate the vertex function for the
``empty state boson" self-energy, we have devised two approximations which
reduce much computational efforts without losing general features of the model.
It is found that the Kondo temperature is reduced by the presence of a magnetic
field, and that at low field and at low temperature, the field dependence of
both the Kondo temperature and the impurity magnetization exhibits a scaling
behavior with high accuracy. Further, some interesting features are found in
the field dependence of the impurity magnetization at finite temperature, the
physical implications of which are discussed in terms of the renormalized Kondo
temperature.Comment: 18 pages Revtex, 7 Postscript figures, To appear in Phys.Rev.