Magnetic Properties and Large SHG Response of a Chiral Ternary Chalcogenide: Eu2SiSe4

Eu(II)-containing chalcogenides are an emerging class of materials that are of high 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. We find the second harmonic generation (SHG) activity (~7x AGS) of polycrystalline Eu2SiSe4 to be 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 vibrations of the SiSe4 tetrahedra. We investigate the physical properties of Eu2SiSe4 and find complex temperature- and field-dependent behavior, including a weak transition at ~145 K as well as multiple magnetic transitions occurring at low temperature, leading to a slightly canted antiferromagnetic or ferrimagnetic ground state. The low-temperature transitions release less entropy than expected, which may be due to complex crystal electric field effects of Eu(II).