Muon spin rotation and relaxation measurements have been made on the molecular magnetic superconductors κ-BETS2FeCl4 and κ-BETS2FeBr4 and the non-magnetic molecular metals κ-BETS2GaCl4 and λ-BETS2GaCl4. In the magnetic materials, zero field muon spin relaxation signals show the formation of static antiferromagnetically ordered states and multiple precession frequencies are observed, corresponding to muon sites situated both within the anion layers and within the BETS layers. Studies of the relaxation behavior in the FeCl4 salt have previously shown significant changes around its superconducting transition and the FeBr4 salt reveals similar changes in the region of its superconducting transition, whose onset is around 1.5 K. In the non-magnetic GaCl4 salts the formation of a superconducting vortex lattice was observed and the penetration depth λ was derived from the transverse field muon relaxation. When the BETS superconductors are compared with the ET-based superconductors that we have already studied using μSR, a striking correlation was observed between Tc and λ-3.
ASJC Scopus subject areas