Exponential field distribution in Sr(Cu1-xZnx)(2)O-3

We discuss the use of the Kubo Golden rule (KGR) in the derivation of new m uon polarization functions for arbitrary static field distributions in both zero (ZF) and longitudinal (LF) applied fields. ZF/LF muon spin relaxation measurements in spin-ladder system Sr(Cu1-xZnx)(2)O-3 are reported, with o bservations of dilute moment freezing for x less than or similar to 0.008 a nd dense moment freezing for x greater than or equal to 0.008. In neither t he dilute nor the dense case do the data conform to classic muon polarizati on functions. Using the KGR we derive new muon polarization functions to de al with both of these cases. The dilute case assumes dilute moments with a dense moment background, while the dense case assumes an exponential distri bution of fields. Simulation of this system is consistent with an exponenti al distribution of fields. (C) 2000 Elsevier Science B.V. All rights reserv ed.