X-ray linear dichroism study on S = 2 antiferromagnets Ba2FeSi2O7 and Sr2FeSi2O7: determination of single-ion magnetic anisotropy energies

Abstract We investigated S = 2 quasi-two-dimensional XY Heisenberg antiferromagnets Ba 2 FeSi 2 O 7 (BFSO) and Sr 2 FeSi 2 O 7 (SFSO) using the Fe L 2,3 -edge X-ray linear dichroism (XLD). The XLD spectrums exhibit nearly identical spectral line shapes with small variations for BFSO and SFSO, which form isostructural square-lattice magnetic networks of compressed FeO 4 ( d 6 ) tetrahedrons. For the XLD line shape analysis, we performed the full multiplet cluster model calculations and successfully reproduced not only the spectral line shape but also small variations through different degrees of the compressive distortion for BFSO and SFSO. The model calculations confirm that the S = 2 5 E g ( t 2g 3 e g 3 ) state is split into S z = 0, ± 1, and ± 2 by the spin–orbit coupling. In the analysis, we found that the splitting energy D , denoted as the single-ion magnetic anisotropy energy of the order of 1 meV scale, varies with the degree of the distortion and determined D BFSO = 1.45 meV and D SFSO = 1.22 meV.