Paramagnetic contribution to the magnetic susceptibility of Bechgaard salts

Summary  The crystal of Bechgaard salt (TMTSF)2X) is considered as a system of defect-bounded finite-length fragments of the TMTSF stacks. The paramagnetic contribution χspin to the susceptibility of the system arises due to the thermal population of the triplet excited states of the fragments and considerably increases with temperature in accordance with experiment. The unusual dependence of the pressure fractional derivative of χspin on temperature is explained as well. For the average fragment length flowing to infinity our expression for χspin transforms into the known Pauli formula and becomes temperature independent.