Study of Field-Induced Magnetic Order in Singlet-Ground-State Magnet CsFeCl${}_3$

Abstract

The field-induced magnetic order in the singlet-ground-state system CsFeCl${}_3$ has been studied by measuring magnetization and neutron diffraction. The field dependence of intensity for the neutron magnetic reflection has clearly demonstrated that the field-induced ordered phase is described by the order parameter $<S_x>$. A condensate growth of magnons is investigated through the temperature dependence of $M_z$ and $M_{\perp }$, and this ordering is discussed in the context of a magnon Bose-Einstein condensation. Development of the coherent state and the static correlation length has been observed in the incommensurate phase in the field region of $5<H<6$ T at 1.8 K. At $H>H_{\mathrm{c}}$, a satellite peak was found in coexistence with the commensurate peak at the phase boundary around 10 T, which indicates that the tilt of the c-axis would be less than $\sim 0.5^{\circ }$ in the whole experiments.

5 pages, 5 figures