Effect of Zn doping on the antiferromagnetism in kagomeCu4−xZnx(OH)6FBr

Abstract

Barlowite Cu4(OH)6FBr shows three-dimensional (3D) long-range antiferromagnetism, which is fully suppressed in Cu3Zn(OH)6FBr with a kagome quantum spin liquid ground state. Here we report systematic studies on the evolution of magnetism in the Cu4−xZnx(OH)6FBr system as a function of x to bridge the two limits of Cu4(OH)6FBr (x=0) and Cu3Zn(OH)6FBr (x=1). Neutrondiffraction 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 Cu 2+ sites on the kagome planes are found to be vanishingly small, suggesting strong frustration already exists in barlowite. Substitution of interlayer Cu 2+ with Zn 2+ 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 ∼ 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)6FBr 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.

Magnetic resonance as a local probe for kagomé magnetism in Barlowite Cu4(OH)6FBr

“…Here, strong residue spin fluctuations, in the form of intralayer spin singlet formation due to the structure distortion (both displacements of Cu2 and deformation of kagome planes), are reported below magnetic transition at 15 K. 35 For systems with unique and homogeneous relaxation rate, the value of the stretch exponent will be β = 1. In contrast, a reduced value of β (< 1) indicates a wide distribution of relaxation rates.…”

“…The local structure of barlowite may not be well described by the average hexagonal model, a conclusion that goes in line with the very recent diffraction studies reporting orthorhombic symmetry of the crystal structure. 34,35 Insights into the spin dynamics can be obtained by measuring the spin lattice relaxation rates (1/T 1 ) as a function of temperature. 79 Br and 81 Br nuclear spin-lattice relaxation time T 1 were measured using a conventional inversion recovery pulse sequence at 84.44 MHz (at 7.4 T for 81 Br and 8.2 T for 79 Br).…”

Antiferromagnetism in the kagome-lattice compound α−Cu3Mg(OH)6Br2

“…α-Cu 3 Mg(OH) 6 Br 2 was synthesized by the hydrothermal method as described previously 26,39 . The mixture of 1.5-mmol Cu 2 (OH) 2 CO 3 and 6-mmol MgBr 2 •6H 2 O was sealed in a 50-ml reaction vessel with 25-ml water, which was slowly heated to 200 • C and kept for 12 hours.…”

“…The idea for the compound of Cu 3 Mg(OH) 6 Br 2 comes from the substitution of interlayer Cu 2+ in the barlowite Cu 4 (OH) 6 FBr, which has perfect Cu 2+ kagome layers with Cu 2+ ions between them and is antiferromagnetically ordered at about 15 K [36][37][38][39][40] . It has been theoretically suggested that Zn 2+ or Mg 2+ ions can replace the interlayer Cu 2+ in barlowite and thus dilute the AF order to give rise to a QSL state as in herbertsmithite 41,42 .…”

“…It has been theoretically suggested that Zn 2+ or Mg 2+ ions can replace the interlayer Cu 2+ in barlowite and thus dilute the AF order to give rise to a QSL state as in herbertsmithite 41,42 . While this proposal has been shown to succeed in Cu 3 Zn(OH) 6 FBr [26][27][28]39,43 , no Mgsubstituted barlowite has been reported. In this paper, we follow the same route in synthesizing the Znsubstituted barlowite to grow Mg-substituted barlowite.…”