Stability of quantum spin liquids in two dimensionsArh, Tina (Avtor) Zorko, Andrej (Mentor) quantum spin liquidsfrustrated magnetismquantum materialskagome latticetriangular latticeYCu$_3$(OH)$_6$Cl$_3$Zn-barlowiterare-earth heptatantalatesQuantum spin liquid is a disordered but strongly quantum-entangled ground state of matter that can occur in layered materials with geometrically frustrated lattices of magnetic ions, such as the triangular and the kagome lattice. Although quantum spin liquid can arise as a ground state of an isotropic nearest-neighbour Heisenberg model, it can be stabilized or destabilized by various perturbations of this model, such as magnetic anisotropy or further-neighbour interactions. In this work, we first study the quantum magnet YCu$_3$(OH)$_6$Cl$_3$, in which copper ions form well-separated kagome layers. This material is magnetically ordered at low temperatures, although a quantum spin liquid ground state is expected due to dominant nearest-neighbour interactions. Using electron spin resonance, magnetic susceptibility, and specific heat measurements, we show that the magnetic order is stabilized by the Dzyaloshinskii-Moriya magnetic anisotropy. Nuclear magnetic resonance is used to characterize the local magnetic fields and their fluctuations. In zinc-doped barlowite, another representative of quantum kagome antiferromagnets, experiments suggest a quantum spin liquid ground state, but its characterization is challenging due to the presence of magnetic defects. Using nuclear magnetic resonance and magnetic susceptibility measurements, we show that the amount of defects in this material is higher than previously reported. We successfully separate the contributions of intrinsic spins and magnetic defects in the nuclear magnetic resonance spectra and determine the local magnetic susceptibility. Finally, we study rare-earth heptatantalates in which neodymium or erbium ions form the triangular lattice in well-separated layers. Rare earths are known for anisotropic exchange interactions, which we show to have a strong Ising-type anisotropy using inelastic neutron scattering, magnetic susceptibility and electron spin resonance. In neodymium heptatantalate, measurements also reveal the short-range spin correlations of Ising character. Nevertheless, the material is not ordered to the lowest experimentally accessible temperatures and is a quantum spin liquid candidate.20242024-06-29 08:15:04Doktorsko delo/naloga159093sl