Structure, chromium vacancies, and magnetism in a C r12-x T e16 compound

Binary Cr-Te compounds are known to exhibit various structures and interesting physical properties, which are very sensitive to Cr content and arrangement. We report the structure and physical properties of a compound Cr12-xTe16 with x∼2.65. Cr9.35Te16 crystallizes in the trigonal structure with the space group P3m1 (No. 164), consisting of four different Cr sites (Cr1, Cr2, Cr3, Cr4) with an ordered Cr4 vacant layer. The electrical resistivity, magnetization, specific heat, and neutron diffraction measurements indicate that there is a ferromagnetic transition at TC1∼160 K with the first-order nature, and an anomaly at TC2∼67 K. At 5 K, the magnetic moments of Cr2 and Cr3 are aligned along the c axis with 2.78μB/Cr. Detailed neutron diffraction refinement suggests that ordered magnetic moments on Cr1 (fully occupied) and Cr4 (partially occupied) are negligible. The different magnetic response stems from different valence states and different magnetic interactions between Cr2/Cr3 and Cr1/Cr4 as evidenced by the x-ray absorption fine-structure measurements. This creates a unique two-dimensional magnetic system with ordered moments confined in the Cr2/Cr3 layer.