6.1 Summary of Previously Reported $\mu {\cal SR}$ Results

$\mu {\cal SR}$ results on each of these systems have been published previously, see [168,202,203,204] and currently further ZF data by the group that published [204] exists, but has not yet been reported except in very brief form in [205]. These experiments have concentrated on the low temperature magnetic phase (A = Rb, Cs), and use mainly the ZF technique.

The conclusions of these works mainly address the the SDW conjecture offered to explain the ESR measurements[65]. All the measurements agree that the low temperature relaxation observed is due to a distribution of static fields. While the authors of [168,204] concluded that the distribution was essentially random, the authors of [202] concluded that the data was not inconsistent with a disordered SDW, but may also be consistent with some other form of antiferromagnetism [203]. Recently, measurements for (A = Rb, Cs) have been reported[205] down to 100mK, with no qualitative change of the relaxation below about 2K. The report, though, was very brief, and the experimental procedure was not described. The only reported measurements of $\mu {\cal SR}$ for A = K are those of [203]. The conclusion of these measurements is simply that unlike the other materials, there is no magnetic ordering in this system. down to 2.5K