Thermodynamics of field-induced spin-density-wave states in Bechgaard salts. II

Extending the Gor'kov and Lebed approach to more general spin-density-wave (SDW) vectors, we study theoretically the thermodynamics of the field-induced SDW in Bechgaard salts. The quasiparticle spectrum in the SDW is determined. The thermodynamics is identical to that for a BCS superconductor. We predict a cascade of SDW transitions in magnetic fields, which describes the observed phase diagram of the relaxed bis(tetramethyltetraselenafulvalene)perchlorate [(TMTSF)₂{ClO}₄$] extremely well. We calculate also the magnetization in SDW, which again describes the observed magnetization in (TMTSF${)}₂ClO₄ quite well.