Low-temperature high-field X-ray absorption spectroscopies

Abstract:   High-field X-ray absorption spectroscopies can provide valuable information for paramagnetic materials and antiferromagnetic systems. The effective magnetic moment of BaCoO₃ estimated from the magnetic susceptibility is 2.23 μ_B larger than 1.73 μ_B expected for low-spin Co⁴⁺. The deviation might be attributed to non-zero orbital moment, while the elongation of the CoO₆ octahedron would result in the hole occupation of the a_1g orbital with m=0. By use of X-ray magnetic circular dichroism (XMCD) combined with theoretical simulations, we found the the hole would occupy at the e_g orbital owing to the short distance between Co ions along the c axis which also leads to the finite orbital moment of Co. On the other hand, the antiferromagnetic structure of TbFe₃(BO₃)₄ and the modifications under external magnetic field were detected via X-ray linear dichroism and XMCD. The enhancement of the magnetization in the antiferromagnetic phase can be attributed to not only the flop of the Fe moment but also the increase of the Tb moment.