Anonlalous enhancement of g-shift in k-type BEDT-TTF compounds

Summary form only given. Systematic investigation of the ESR properties of k-type BEDT-TTF compounds has been carried out. The salts with crystal symmetry of P2/sub 1/, k-(BEDT-TTF)/sub 2/CU(CN)[N(CN/sub 2/, k-Cu(NCS)/sub 2/ and k-Ag(CN)/sub 2/-H/sub 2/0, were found to show an anomalous enhancement of g-shift below about 150K when the static field was applied along b-axis. Concomitantly, abrupi broadening of the linewidth has been observed in all principal axes. On the other hand, k-Cu[N(CN)/sub 2/]Br (P/sub nma/) and k´-CU/sub 2/(CN)/sub 3/ (P2/sub 1/c/) have ahnost temperature independent g-values for all principal axes. In spite of highly isotropic donor packing in conduction layers of the k-type compounds, the large g-shift was only observed along the b-axis. This rules out the simple explanation as due to the change in the molecular orientations at low temperatures. It is now an open question that the g-value observed in P2/sub 1/ group is true one. We will check the frequency dependence of the resonance field and discuss possible mechanisms of the large g-shift.