Magnetic Properties and Large Second-Harmonic Generation Response of a Chiral Ternary Chalcogenide: Eu2SiSe4
来源：ACS Publications
Eu(II)-containing chalcogenides are an emerging class of materials that are of great interest due to their high optical activity and intriguing magnetism. Here, we synthesized Eu2SiSe4 as red-colored single crystals and characterized its structure with single-crystal X-ray diffraction, confirming the reported chiral monoclinic P21 symmetry at room temperature. The crystal structure of Eu2SiSe4 comprises distorted SiSe4 tetrahedral units and charge-balancing Eu(II) cations. Here, we develop a two-step solid-state synthesis method for Eu2SiSe4 and compare it to the known boron chalcogenide method. We find the second-harmonic generation (SHG) activity of polycrystalline Eu2SiSe4 to be ∼7 × AgGaS2, placing it among the highest-known SHG-active chalcogenides. No symmetry lowering is observed down to 100 K in single-crystal X-ray diffraction, although an anomalous expansion in the b-axis lattice parameter occurs and may be correlated to lattice modes of the SiSe4 tetrahedra. We investigate the physical properties of Eu2SiSe4 using magnetometry and heat capacity measurements and find a transition to an antiferromagnetic ground state at TN ≈ 5.5 K. The low-temperature transition releases less entropy than expected, which may be due to the complex crystal electric field effects of Eu(II).
In this work, we successfully synthesized Eu2SiSe4 as single crystals and bulk crystalline powder using both the BCM technique and a two-step solid-state synthesis method. In addition to confirming the room temperature crystal structure, we also performed single-crystal X-ray diffraction at 100 K and found a subtle, and unusual, structural change involving increasing Eu–Se bond distances at low temperature. The chiral nature of the compound was further validated via SHG, where the SHG response is one of the largest reported to date. Finally, the magnetic and thermodynamic properties were characterized for the first time, revealing a transition to an antiferromagnetic ground state at TN ≈ 5.5 K. We discuss how the synthesis method influences the presence of impurities (namely EuSe) and complicates measurement of the intrinsic properties of Eu2SiSe4.