Magnetic measurements were performed on R2Co7B3 (R = Ho, Er,Tm) compou
nds in the temperature range 2-800 K and external fields of up to 70 k
Oe. The compounds are ferrimagnetically ordered. From the Curie consta
nts determined in a high temperature range, effective cobalt moments,
M(eff)(Co) = 2.30 +/- 0.10 mu(B) are also determined. The magnetic beh
aviour of cobalt in the compounds studied is analyzed in the spin fluc
tuations model.