Magnetic phase diagram of the linear quantum ferro-antiferromagnet Cs2Cu2Mo3O12

A single-crystal sample of the frustrated quasi-one-dimensional quantum magnet ${\mathrm{Cs}}₂{\mathrm{Cu}}₂{\mathrm{Mo}}₃{\mathrm{O}}₁₂$ is investigated by magnetic and thermodynamic measurements. A combination of specific heat and magnetic torque measurements maps out the entire $H\text{\ensuremath{-}}T$ 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 multimagnon 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.