Thermodynamic properties, electron spin resonance and underlying spin model in Cu₃Y(SeO₃)₂O₂Cl

We report a detailed study of the magnetic properties of the buckled kagome compound Cu₃Y(SeO₃)₂O₂Cl using heat capacity, magnetization, powder neutron diffraction, electron spin resonance and first-principles calculations. The crystal structure is confirmed to be isotypic with the mineral francisite, with orthorhombic space group symmetry Pmmn throughout the temperature range 5 – 300 K. Magnetization, heat capacity and neutron diffraction confirm long range magnetic order below T_N = 35 K. The electron spin resonance spectra reveal the presence of two modes corresponding to two different crystallographic Cu positions. The principal g-values of the g-tensor of Cu(1) sites were found to be g₁ = 2.18(4), g₂ = 2.10(6) and g₃ = 2.05(9), while the effective g-factor of Cu(2) sites is almost isotropic and is on average g = 2.09(5). At low temperatures, Cu₃Y(SeO₃)₂O₂Cl undergoes a metamagnetic transition, with a critical field BC = 2.6 T at 2 K, due to the suppression of the inter-plane exchange interactions and saturates in modest magnetic field, B_S ≤8 T. The first-principles calculations allow an estimation of both intra-plane and inter-plane exchange interactions. The weakness of the inter-plane exchange interaction results in low values of the critical fields for the metamagnetic transition, while the competition between intra-plane exchange interactions of different signs results in a similarly low value of the saturation field.