O observed in magnetic fields of up to 73 T*

The four inequivalent Cu ions in the novel chiral chain compound [Cu(pym)(H₂O)₄]SiF₆ ^. H₂O experience a staggered local environment with an extra twist: a four-fold chiral structure. The consequent hierarchy of competing interactions leads to unconventional magnetic-field-dependent behavior. In this study we report measurements of the magnetization and magnetocaloric effect of single crystals of [Cu(pym)(H₂O)₄]SiF₆ H₂O in magnetic fields of up to 73 T and at temperatures down to 0.5 K. Field orientations parallel and perpendicular to the chains were used. The data reveal several unusual features, including a field-induced quantum-critical phase transition close to saturation magnetization that is absent in more conventional Sine-Gordon chains.