WEAK FERROMAGNETISM BELOW 12 K IN A LITHIUM TETRAFLUOROTETRACYANOQUINODIMETHANIDE SALT

The spin interaction between TCNQF(4)(-') molecules in the Li+, Na+, K +, Rb+, Csf and NMe(4)(+) salts was investigated in the temperature ra nge of 2 to 300 K. The other salts than Li+ TCNQF(4)(-)' exhibited alm ost temperature-independent small susceptibilities, indicating disappe arance of the free radical moments. On the other hand, the susceptibil ity of the Li+ salt obeyed a Curie-Weiss law above 50 K with a Curie c onstant of 0.36(1) emu K mel(-1) and an asymptotic Curie temperature o f - 30(2) K. A sudden enhancement of the susceptibility was observed a t 12 K. These results suggest an antiferromagnetic ordering of the rad ical anions accompanied with spin cantings (weak ferromagnetism) in th e Li+ salt below 12 K.