Magnetic response of spin-density waves in a quasilinear half-filled Hubbard band

Abstract

The linear and nonlinear response of spin-density waves (SDW) to a magnetic field is studied in a quasi-one-dimensional half-filled Hubbard band within a mean-field approximation. We find that the linear transverse susceptibility remains nearly temperature independent below the SDW transition, while the longitudinal susceptibility drops exponentially with the temperature. At low fields we prove that the free energy is minimum when the field is perpendicular to the spontaneous magnetization and maximum when it is parallel. Regardless of its magnitude, a transverse field is shown to have no significant effect on the temperature dependence of the spontaneous magnetization and the susceptibility in agreement with data. On the other hand, a large longitudinal field destroys the SDW. In this case the free energy is maximum and a much lower energy is obtained by reorienting the spontaneous magnetization perpendicular to the field. The relevance of the results to the organic conductors ${(\mathrm{TMTSF})}_{2}X$ (tetramethyltetraselenafulvalene; $X=\mathrm{P}{\mathrm{F}}_{6} \mathrm{and} \mathrm{As}{\mathrm{F}}_{6}$) is discussed.