Field-induced magnetic order in bis-tetramethyltetraselenafulvalenium perchlorate(TMTSF)2ClO4

A microscopic study of the organic superconductor bis-tetramethyltetraselenafulvalenium perchlorate [${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$Cl${\mathrm{O}}_4$] has been undertaken with the use of nuclear magnetic resonance techniques. Proton and selenium resonances were recorded over the field range 60-120 kOe at a temperature of 1.5 K. The proton spin-lattice relaxation-rate measurements clearly reflect both the high-field phase transition and magnetotransport anomalies. The selenium resonance is strongly attenuated above the high-field transition which indicates the onset of field-induced magnetic order. These results and their bearing on the high-field electronic properties of the Bechgaard salts are discussed.