Structural order and disorder within novel antiferromagnetic RCrxGa3-yGey and R4Cr1-xGa12-yGey intermetallic compounds (R = Tb, Dy)

Single crystals of intermetallic phases RCr x Ga 3−y Ge y (R = Tb, Dy; x = 0.19–0.23, y = 0–0.4) and R 4 Cr 1−x Ga 12−y Ge y (R = Tb, Dy; x = 0–0.13, y = 3–4) were grown from Ga flux ensuring the absence of magnetic impurities . The X-ray diffraction experiments revealed that the compounds belong to the family of filled AuCu 3 -type gallides. The compounds are formed upon the insertion of Cr atoms into E 6 octahedral voids (E = Ga/Ge), which can occur in either disordered (RCr x Ga 3-y Ge y ) or ordered (R 4 Cr 1-x Ga 12-y Ge y ) fashion. The unique feature of the obtained compounds is the strong correlation between the level of Ge doping and the Cr concentration in the phases, which allows one to control both the structural and magnetic ordering. At low Ge concentration, the cubic RCr x Ga 3-y Ge y phases form, which then experience tetragonal distortion upon the increase in the Ge content, and the cubic R 4 Cr 1-x Ga 12-y Ge y 2×2×2 superstructures are formed at even higher Ge concentrations. The X-ray diffraction analysis also showed a presence of structural defects in the phases, which are caused by different size of empty E 6 and filled CrE 6 octahedra . Magnetic measurements of the single crystals of the cubic phases reveal antiferromagnetic ordering of the rare earth sublattice with the Neel temperatures decreasing upon Ge doping from 22 K for RCr x Ga 3 to 10 K for R 4 Cr 1−x Ga 12−y Ge y . The Ge doping causes gradual decrease in the strength of antiferromagnetic R-R interactions ultimately leading to noncollinear magnetic structure in the superstructure R 4 Cr 1−x Ga 12−y Ge y phases. • Single crystals of RCr x Ga 3-y Ge y and R 4 Cr 1-x Ga 12-y Ge y (R = Tb, Dy) are synthesized from Ga flux. • RCr x Ga 3-y Ge y phases feature disordered alternation of empty and Cr-filled (Ga,Ge) 6 octahedra . • In superstructure R 4 Cr 1-x Ga 12-y Ge y phases, Cr(Ga,Ge) 6 octahedra form body-centered lattice. • The Ge concentration in phases determines both the Cr content and its structural ordering. • All investigated compounds demonstrate antiferromagnetic ordering below 22 K.