Electron paramagnetic resonance and magnetically modulated microwave absorption experiments on κ-(BEDT—TTF)2Cu[N(CN)2]Cl

Electron paramagnetic resonance (EPR) and magnetically modulated microwave absorption (MMMA) measurements were taken on differently prepared samples of the quasi two-dimensional organic conductor κ-(BEDT—TTF)2Cu[N(CN)2]Cl to study the interesting pressure dependent phase transition of this charge-transfer compound. The MMMA results undoubtedly confirm that the substance becomes a superconductor below 12.5 K, if a moderate pressure, e.g. just by embedding the substance in silicon grease during cooling, is applied. At an onset temperature of 25 K an additional microwave absorption is observed, which is about a factor of 100 weaker than the superconducting MMMA signal. We relate this microwave absorption to an antiferromagnetic ordering resulting in weak ferromagnetism by spin-canting occurring at this temperature. The result corresponds to the EPR measurements, where considerable changes in the main EPR parameters, i.e. linewidth, signal amplitude and susceptibility, are observed, giving evidence for an antiferromagnetic ordering below 50 K and a change to weak ferromagnetism below 25 K.