(BiSe)_1.23CrSe₂ and (BiSe)_1.22(Cr_1.2Se₂)₂: Magnetic anisotropy in the first structurally characterized Bi-Se-Cr ternary compounds

Compounds containing both heavy main group elements and paramagnetic transition metals form a fertile area for the study of magnetic anisotropy. We pursued the synthesis, characterization, and magnetic measurements of Bi-Se-Cr compounds: a ternary system with no structurally characterized materials. Those efforts led to the isolation of two novel misfit layer compounds, namely, (BiSe)_1.23CrSe₂ (1) and (BiSe)_1.22(Cr_1.2Se₂)₂ (2). The crystal structure of 1 consists of alternating BiSe and CrSe₂ layers along the c-axis, and 2 is composed of alternating BiSe and (Cr_1.2Se₂)₂ layers along the c-axis. Lattice mismatch occurs in both compounds along the b-axis and leads to positional modulation of the atoms. Field- and temperature-dependent measurements were performed to assess the degree of magnetic anisotropy. Temperature-dependent susceptibility measurements on aligned crystals of 1 display increased bifurcation of zero-field cooled and field cooled data when crystals are oriented with H perpendicular to c than when the crystals are oriented with H parallel to c. Magnetic anisotropy is less pronounced in 2 where both crystallographic orientations exhibit bifurcation at 26 K. The complexity of the magnetic behavior in both compounds likely signifies a competition between CrSe₂ intralayer ferromagnetic coupling and interlayer antiferromagnetic coupling. These results highlight the exciting magnetic properties that can arise from the exploration of new ternary phases.