Magnetic field effects on (TTF)Cu${\mathrm{S}}_4$${\mathrm{C}}_4$${\left(\mathrm{C}{\mathrm{F}}_3\right)}_4$, a spin-Peierls system

We present neutron scattering data in magnetic fields up to 80 kG and magnetization data up to 150 kG for the spin-Peierls system (TTF)Cu${\mathrm{S}}_4$ ${\mathrm{C}}_4$ ${\left(\mathrm{C}{\mathrm{F}}_3\right)}_4$. The spin-Peierls transition temperature is depressed by the field, in reasonable agreement with mean-field theory, and the nonmagnetic spin-Peierls phase disappears above ∼125 kG. We discuss details of the observed behavior in the light of existing theory. We show that the behavior is different from that of a quasi-one-dimensional magnetic system which orders antiferromagnetically, because of the contrasting role of fluctuations.