Relaxation in the insulating spin glass Co1−xMnxCl2⋅2H2O (abstract)

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Abstract
Previous magnetization and susceptibility measurements on the mixed magnet Co1−xMnxCl2⋅2H2O disclosed a spin glass transition near 2.45 K over a wide composition range.1 Recent heat capacity and NMR measurements have confirmed and extended this finding.2 The time dependence of the thermoremanent magnetization (TRM) below Tg for an x=0.452 mixture was studied in some detail1 and was found to conform approximately to a decay of stretched exponential type, or perhaps slightly more accurately to the product of a stretched exponential and a power law. Small systematic deviations of data from fitted curves were apparent however. Recently a percolation model for relaxation in random systems was proposed,3 and yielded significantly improved fits to the TRM decay in an Au:Fe spin glass. The model assumes dispersive excitations within fixed finite domains, and includes as parameters the fastest and slowest relaxation rates characterizing the spectrum of domains. We find that this model also permits much better fits to be obtained for the TRM decay in Co1−xMnxCl2⋅2H2O, x=0.452. Systematic deviations that were present when using more traditional decay functions are virtually eliminated. The variation of fitted parameters with cooling field and temperature is also explored.