ceptihility of Sr3CuPtc jIr,,j06 follolvs the predicted behavior of a random quantum spin chain (Figs. 3 and 4). A t high temperatures, the susceptibility has a linear x versus 1/T dependence and is Curie-like. In this regime, where there is 110 ordering among unpaired electrons, the spins act independently. A fit of the high-temperature data ga17e a Weiss constant of 8 = -12.7 K and a spin-only tnotnent of (I, = 2.11 Bohr magnetons. This moment is in excelle~lt agreement with that expected for a sample containing, on a17erage, one S = ?h Cu ion and o~le-half S = lh Ir ion, nhich should yield an effecti1.e moment of (I, = 2.12. A t lon.er temperatures, there is a t r a n sition to a regime where spin-spill interactions hecome important, as indicated by the broad cur17e in the inl~erse susceptibility. This transition marks the alignment of spins to form islands of effecti1.e spins, as discussed above. Comparison of Figs. 3 and 4 sho\vs that theory and experiment are in good agreement.

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