SIMULATION OF THE EFFECT OF REORIENTATION ON THE ELECTRON-SPIN ECHO DECAYS USING THE STOCHASTIC LIOUVILLE FORMALISM - APPLICATION TO INTERSTITIAL HYDROGEN IN SRF2 AND BAF2

The thermal evolution of the two pulses (2p) electron spin echo (ESE) decay of interstitial atomic hydrogen formed in hydrolysed SrF2 and Ba F2 is studied. The influence of the atomic jumps along the [110] direc tions, that go from the static to the fast motion limit, is included i n order to simulate the 2p-ESE decays. An extension of the Stochastic Liouville formalism is developed, which gives explicit expressions for the 2p-ESE decay signals in the case of paramagnetic impurities that can reorient among a discrete number of sites. A comparison between th e calculated decays and the experimental ones provides information abo ut the effective displacement of the minima of the multiwell potential in which interstitial hydrogen moves. A discussion of the results tak ing into account the structure of the host lattices is also given. (C) 1998 Elsevier Science Ltd. All rights reserved.