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

TL;DR

This study investigates field-induced magnetic ordering in CsFeCl$_3$, revealing magnon Bose-Einstein condensation and phase coexistence through magnetization and neutron diffraction measurements.

Contribution

It provides experimental evidence of magnon BEC and detailed phase behavior in CsFeCl$_3$, linking magnetic order to condensate growth and incommensurate phases.

Findings

Field-induced order described by <S_x>

Observation of magnon condensate growth

Coexistence of incommensurate and commensurate peaks

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 $H > H_{\rm c}$, 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.