Materials constructed from kagomé layers of antiferromagnetically coupled S = ½ moments are highly prized as they offer a unique opportunity to explore the elusive quantum spin liquid state (QSL).[1] Recently, the Cu²⁺-based mineral known as Zn-doped barlowite, ZnCu3(OH)6FBr, has shown promise as a new materialization of the QSL state.[2] Despite this interest, the crystal and magnetic structures of the parent material barlowite, Cu4(OH)6FBr, are poorly understood with several conflicting reports in the literature.[3-5] Here, I will introduce these developments in the field of highly frustrated magnetism before presenting our comprehensive powder neutron diffraction study of barlowite. In doing so, I will discuss the intriguing structural phase transition we observe in this material at T = 250 K, and clarify the nature of the magnetic ground state below TN= 15 K.[6] Furthermore, I will show that we can tune the magnetic ground state of barlowite from antiferromagnetic order to quantum disorder upon Zn-doping though magnetometry and muon spectroscopy measurements. Finally, I will discuss efforts to control the nature of the structural phase transition within a new family compounds through exchange of the halide ions in barlowite.

[1] Savary, Balents, Rep. Prog. Phys. 80, 016502 (2017).

[2] Han, Singleton, Schlueter, Phys. Rev. Lett. 113, 227203 (2014).

[3] Feng et al., Phys. Rev. B 98, 155127 (2018).

[4] Pasco et al., Phys. Rev. Mater. 2, 0444061 (2018).

[5] Smaha et al., J. Solid State Chem. 268, 123-129 (2018).

[6] Tustain et al., Phys. Rev. Mater. 2, 111405(R) (2018).

Materials Research Laboratory and Materials Department