Effect of Zn doping on the antiferromagnetism in kagome Cu4-xZnx(OH)(6)FBr

Barlowite Cu-4(OH)(6)FBr shows three-dimensional (3D) long-range antiferromagnetism, which is fully suppressed in Cu3Zn(OH)(6)FBr with a kagome quantum spin liquid ground state. Here we report systematic studies on the evolution of magnetism in the Cu4-xZnx(OH)(6)FBr system as a function of x to bridge the two limits of Cu-4(OH)(6)FBr (x = 0) and Cu3Zn(OH)(6)FBr (x = 1). Neutron-diffraction measurements reveal a hexagonal-to-orthorhombic structural change with decreasing temperature in the x = 0 sample. While confirming the 3D antiferromagnetic nature of low-temperature magnetism, the magnetic moments on some Cu2+ sites on the kagome planes are found to be vanishingly small, suggesting strong frustration already exists in barlowite. Substitution of interlayer Cu2+ with Zn2+ with gradually increasing x completely suppresses the bulk magnetic order at around x = 0.4 but leaves a local secondary magnetic order up to x similar to 0.8 with a slight decrease in its transition temperature. The high-temperature magnetic susceptibility and specific-heat measurements further suggest that the intrinsic magnetic properties of kagome spin liquid planes may already appear from x > 0.3 samples. Our results reveal that the Cu4-xZnx(OH)(6)FBr may be the long-thought experimental playground for the systematic investigations of the quantum phase transition from a long-range antiferromagnet to a topologically ordered quantum spin liquid.