EPR properties in alpha-(BEDT-TTF)(2)MHg(SCN)(4) M=(NH4, Rb)

EPR study of the organic conductors, alpha-(BEDT-TTF)(2)M Hg(SCN)(4) M=(NH4, Rb) was performed. The observed line is always single Lorentzian down to the lowest temperature similar to 10 K in contrast to the previous report. The spin susceptibility and the g-values of the NH4 salt are almost temperature independent. For the Rb salt, the spin susceptibility exhibits an abrupt drop by half below 13 K. At the same time, slight change in the g-values is observed. The detailed analysis of the g-tensor reveals that the principal values change at this temperature while their average remains constant. EPR relaxation rate in the Rb salt measured by the saturation method shows no anomaly around this temperature. The electronic structure of the low temperature phase is discussed.