Zero field muon spin relaxation study of the low temperature state in α-(BEDT-TTF)2KHg(SCN)4

Zero field muon spin relaxation measurements are reported for the low temperature magnetic phase of the organic metal (BEDT-TTF)2KHg(SCN)4. Steplike changes in the relaxation rate indicate two transitions; the first occurs around 12 K and is accompanied by a change in the shape of the relaxation function. A further increase in the relaxation rate occurs below 8 K. These changes signify the onset of an internal magnetic field distribution below the transition, which is assigned to a spin-density-wave (SDW) ordering with an estimated amplitude of ∼3×10-3μB below 8 K. This very small value is consistent with the upper limits set by previous magnetic resonance studies and also with a simple mean field description of the SDW transition.