Cr_2.37Ga₃Se₈: A Quasi-Two-Dimensional Magnetic Semiconductor

We present a novel magnetic semiconductor, Cr_2.37Ga₃Se₈, synthesized by partially replacing magnetic Cr³⁺ in antiferromagnetic Cr_5+δSe₈ with nonmagnetic Ga³⁺. The crystal structure of Cr_2.37Ga₃Se₈ was determined by both powder and single-crystal X-ray diffraction. The title compound crystallizes in a monoclinic structure with space group C2/ m (No. 12). In Cr_2.37Ga₃Se₈, the Cr atoms are surrounded by 6 Se atoms and form filled octahedral clusters, while Ga atoms are centered in the Se₄ tetrahedral clusters. The two kinds of clusters pack alternatingly along the c-axis, which results in a quasi-two-dimensional layered structure. The magnetization ( M) measurement shows the development of short-range ferromagnetic coupling below the Curie-Weiss (CW) temperature θ_CW ∼ 92 K, evidenced by the nonlinear field dependence of M. However, the magnetic susceptibility exhibits a peak at low fields at ∼18 K, indicating the existence of an antiferromagnetic interaction as well. Electronic structure calculations using the WIEN2k program in the local spin density approximation indicate that the magnetism arises exclusively from local moments of the Cr atoms. The electrical resistivity measurement of the Cr_2.37Ga₃Se₈ sample confirms that this material is a semiconductor with the band gap ∼0.26 eV. Meanwhile, the experimental band gap (∼0.26 eV) is close to the theoretical prediction using the WIEN2k program (∼0.35 eV).