Compensation of Effective Field in the Field-Induced Superconductor k-(BETS)2FeBr4 Observed by 77Se NMR
Abstract
We report results of 77Se NMR frequency shift in the normal state of the organic charge-transfer-salt k-(BETS)2FeBr4 which shows magnetic field-induced superconductivity (FISC). From a simple mean field analysis, we determined the field and the temperature dependences of the magnetization mpi of the π conduction electrons on BETS molecules. We found that the Fe spins are antiferromagnetically coupled to the pi electrons and determined the exchange field to be J = -2.3T/muB. The exchange field from the fully saturated Fe moments (5 muB) is compensated by an external field of 12T. This is close to the central field of the FISC phase, consistent with the Jaccarino-Peter local field-compensation mechanism for FISC (Phys. Rev. Lett. 9, 290 (1962)).
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