Magnetic interactions in the tripod kagome antiferromagnet Mg2Gd3Sb3O14 probed by static magnetometry and high-field ESR spectroscopy

We report an experimental study of the static magnetization M(H, T) and high-field electron spin resonance (ESR) of polycrystalline Mg2Gd3Sb3O14, a representative member of the newly discovered class of the so-called tripod kagome antiferromagnets where the isotropic Gd3+ spins (S = 7/2) form a two-dimensional kagome spin-frustrated lattice. It follows from the analysis of the low-T M(H) curves that the Gd3+ spins are coupled by a small isotropic antiferromagnetic (AFM) exchange interaction, vertical bar J vertical bar approximate to 0.3 K. The M(H, T) dependences measured down to 0.5 K evidence a long-range AFM order at T-N = 1.7 K and its rapid suppression at higher fields, >= 4 T. ESR spectra measured in fields up to 15 T are analyzed considering possible effects of demagnetizing fields, single-ion anisotropy, and spin-spin correlations. While the demagnetization effects due to a large sample magnetization in high fields and its shape anisotropy become relevant at low temperatures, the broadening of the ESR line commencing already at T less than or similar to 30 K may indicate the onset of the spin-spin correlations far above the ordering temperature due to the geometrical spin frustration in this compound.