Electron paramagnetic resonance and magnetic properties of composite C-60 : Er

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.