Field Tunable Magnetic Transitions of CsCo2(MoO4)2(OH): A Triangular Chain Structure with a Frustrated Geometry

Identifying and characterizing new magnetic systems with Co2+ ions can enhance our understanding of quantum behavior since Co2+ can host a pseudospin-1/2 magnetic ground state. Understanding the magnetic ground state and the phase diagrams of such systems are central to the development of new theoretical models to described emergent quantum properties of complex magnetic systems. The sawtooth chain compound, CsCo2MoO4_2OH, is one such complex magnetic system and here, we present a comprehensive series of magnetic and neutron scattering measurements to determine its magnetic phase diagram. The magnetic properties of CsCo2MoO4_2OH exhibit a strong coupling to the crystal lattice and its magnetic ground state can be easily manipulated by applied magnetic fields. There are two unique Co2+ ions, base and vertex, with Jbb and Jbv magnetic exchange. The magnetism is highly anisotropic with the b-axis (chain) along the easy axis and the material orders antiferromagnetically at TN = 5 K. The zero field antiferromagnetic phase contains vertex magnetic vectors Co1 aligned parallel to the b-axis, while the base vectors Co2 are canted by 34 and aligned in an opposite direction to the vertex vectors. The spins in parallel adjacent chains align in opposite directions, creating an overall antiferromagnetic structure. At a 3 kOe applied magnetic field, adjacent chains flip by 180° to generate a ferrimagnetic phase. An increase in field gradually induces the Co(1) moment to rotate along the b-axis and align in the same direction with Co2 generating a ferromagnetic structure. Our results demonstrate that the CsCo2MoO4_2OH is a promising candidate to study new physics associated with sawtooth chain magnetism.