Magnetic phase diagram of the linear quantum ferro-antiferromagnet Cs${}_2$Cu${}_2$Mo${}_3$O${}_{12}$

Abstract

A single-crystal sample of the frustrated quasi one-dimensional quantum magnet Cs${}_2$Cu${}_2$Mo${}_3$O${}_{12}$ is investigated by magnetic and thermodynamic measurements.A combination of specific heat and magnetic torque measurements maps out the entire $H$-$T$ phase diagram for three orientations.Remarkably, a new phase emerges below the saturation field, irrespective of the crystal orientation. It is suggested that the presaturation phase represents spin-nematic order or other multi-magnon condensate. The phase diagrams within the long-range ordered dome are qualitatively different for each geometry. In particular, multiple transitions are identified in the field along the chain direction.