Half-Magnetization Plateau in a Spin-3/2 Kagome-Strip-Lattice Na₂Co₃(VO₄)₂(OH)₂

Geometric frustration and quantum fluctuations are key ingredients to new types of complex quantum magnetic ground states. In some non-trivial quantum states, a specific spin arrangement can be stabilized in a range of external magnetic fields, manifesting as a plateau in the M-H curve, known as the magnetization plateau. Magnetization plateaus are previously found in honeycomb and kagome lattices, linking to many-body quantum effects and spin anisotropies. Here, we report a half-magnetization plateau in the newly synthesized kagome-strip-lattice (KSL) material, Na₂Co₃(VO₄)₂(OH)₂. KSL is a one-dimensional variety of a kagome lattice, which consists of alternating hexagonal and triangular motifs along one direction, the strip-direction. Our susceptibility measurements reveal the half-magnetization plateau by applying the field perpendicular to the strip-direction. To understand the origin of the magnetization plateau, we used single crystal neutron diffraction to investigate the evolution of magnetic structures with field. At zero field, the magnetic ground state is a non-collinear antiferromagnetic order with reduced ordered-magnetic moments on all Co sites. By increasing the magnetic field, only 1/3 of the Co sites are flipped to ferromagnetic order, while 2/3 of the Co sites remain small to zero ordered-magnetic moments despite the strong magnetic field. Such robustness in reducing ordered-magnetic moments shows intense magnetic frustration and strong quantum fluctuations in this KSL material. Furthermore, assisted with the local magnetic susceptibility method using polarized neutrons and theoretical simulation, I will discuss the mechanism of forming the resultant ground state and the half-magnetization plateau.