The EPR spectrum of the oxygen-deficient Sm0.5Er0.5Ba2Cu3O6+x mixed phase h
as been investigated in the temperature range of 3.3-20 K. Anomalous behavi
or of the EPR spectrum has been detected below 4 K that may indicate the pr
esence of magnetic centers with singlet ground state and an excitation ener
gy of the order of 1 K. (C) 2000 Elsevier Science B.V, All rights reserved.