The composite C-60 : Er was prepared using a mixture of 90 mol% C-60 and 10
mol% Er2O3 powders exposed under compression 8 GPa at temperature T = 1073
K. The anomalous behavior of the EPR signal of paramagnetic centers C-60() at low temperature is revealed. It is expressed through dramatic growth o
f line width Delta B with a temperature decrease. The resonance field of EP
R has a significant anisotropy which also depends on the temperature. Being
connected tightly with the shape of the sample, the anisotropy reflects fe
rromagnetic properties induced by Er3+ ions. The temperature dependence of
sample magnetization is explained in terms of ferromagnetism in disordered
materials. Values of the Curie transition temperature T-C and the superexch
ange interaction of Er3+ ions through C-60 molecules are found equal to T-C
= 6.9 K and J(Er-Er) = 19.8 meV, respectively. (C) 2000 Elsevier Science B
.V. All rights reserved.