We studied the coercivity in magnets of composition R17Fe83-xBx (R = N
d, Pr and x = 8, 30), using measurements of the coercive field H(c), i
ts angular dependence, and the magnetic viscosity coefficient S(v), fo
r temperatures between 4.2 and 500 K. The results are discussed in rel
ation to a model which does not specifically consider the detailed mec
hanisms involved in magnetization reversal, but which provides informa
tion about the magnetic properties in the activation volume v where ma
gnetization reversal is initiated. It is concluded that the ordering t
emperature in v tends to be slightly smaller than in the bulk and that
the room temperature anisotropy in v is not strongly reduced with res
pect to the bulk value. Finally, a direct evaluation of the dipolar in
teractions is in good agreement with results obtained from H(c)(T).