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)(2)O2Cl 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 Cu1 sites were found to be g(1) = 2.18(4), g(2) = 2.10(6), and g(3) = 2.05(9), while the effective g factor of Cu2 sites is almost isotropic and is on average g = 2.09(5). At low temperatures, Cu3Y(SeO3)(2)O2Cl undergoes a metamagnetic transition, with a critical field B-C = 2.6 T at 2 K, due to the suppression of the interplane exchange interactions and saturates in modest magnetic field B-S <= 8 T. The first-principles calculations allow an estimation of both intraplane and interplane exchange interactions. The weakness of the interplane exchange interaction results in low values of the critical fields for the metamagnetic transition, while the competition between intraplane exchange interactions of different signs results in a similarly low value of the saturation field.