E.P.R. investigation of the incommensurate phase of ThBr4 : Gd3+, through fourth order spin-crystal field interaction

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Abstract
The shape of the E.P.R. line ΔMS : |5/2| → |7/2| for the Gd3+-n.n.n. V(Br-) centre, can be consistently interpreted by assuming a modulated rotation around the c crystal axis of the Th-Br bonds as an essential component of the displacement field in the incommensurate phase. The sensitivity of the local Gd3+ probe arises from the high value of the fourth order parameter b44 linked to the flat configuration of the n.n. Br- tetrahedron. We report preliminary results and we outline possible developments of the present investigation