Pressure Tuning the Mixture of Eu²⁺ and Eu³⁺ in Eu₄Bi₆Se₁₃

The investigation of crystallographic, electronic, and magnetic characteristics, especially the mixed valences of Eu²⁺ and Eu³⁺ under pressure of a novel europium-based bismuth selenide compound, Eu₄Bi₆Se₁₃, presented. This new compound adopts a monoclinic crystal structure classified under the P2₁/m space group (#11). It exhibits distinctive structural features, including substantial Eu-Se coordination numbers, Bi-Se ladders, and linear chains of Eu atoms that propagate along the b-axis. Electronic resistivity assessments indicate that Eu₄Bi₆Se₁₃ exhibits weak metallic behaviors. Magnetic characterization reveals uniaxial magnetic anisotropy, with a notable spin transition at approximately 1.2 T when the magnetic field is oriented along the b-axis. This behavior, coupled with the specific Eu-Eu interatomic distances and the magnetic saturation observed at low fields, supports the identification of metamagnetic properties attributable to the flipping of europium spins. The Curie-Weiss analysis of the magnetic susceptibility measured both perpendicular and parallel to the b-axis and high-pressure partial fluorescence yield (PFY) results detected by X-ray absorption spectroscopy (XAS) reveal the tendency of the material to enter a mixed valent state where the trivalent state becomes more prominent with the pressure increase or temperature decrease.