Large miscibility gap in the Ba(Mn(x)Fe(1-x))(2)As(2) system
|Title||Large miscibility gap in the Ba(Mn(x)Fe(1-x))(2)As(2) system|
|Publication Type||Journal Article|
|Year of Publication||2011|
|Authors||Pandey A, Anand VK, Johnston DC|
|Journal Title||Physical Review B|
The compounds BaMn(2)As(2) and BaFe(2)As(2) both crystallize in the body-centered-tetragonal ThCr(2)Si(2)-type (122-type) structure at room temperature but exhibit quite different unit cell volumes and very different magnetic and electronic transport properties. Evidently reflecting these disparities, we have discovered a large miscibility gap in the system Ba(Mn(x)Fe(1-x))(2)As(2). Rietveld refinements of powder x-ray diffraction (XRD) measurements on samples slow-cooled from 1000 degrees C to room temperature (RT) reveal a two-phase mixture of BaMn(2)As(2) and Ba(Mn(0.12)Fe(0.88))(2)As(2) phases together with impurity phases for x = 0.2, 0.4, 0.5, 0.6, and 0.8. We infer that there exists a miscibility gap in this system at 300 K with composition limits 0.12 less than or similar to x less than or similar to 1. For samples quenched from 1000 degrees C to 77 K, the refinements of RT XRD data indicate that the miscibility gap at RT narrows at 1000 degrees C to 0.2 less than or similar to x less than or similar to 0.8. Samples with x = 0.4, 0.5, and 0.6 quenched from 1100 to 1400 degrees C to 77 K contain a single 122-type phase together with significant amounts of Fe(1-x) Mn(x)As and FeAs(2) impurity phases. These results indicate that the system is not a pseudobinary system over the whole composition range and that the 122-type phase has a significant homogeneity range at these temperatures. Magnetic susceptibility chi, electrical resistivity rho, and heat capacity measurements versus temperature T of the single-phase quenched polycrystalline samples with x = 0.2 and 0.8 are reported. We also report attempts to grow single crystals of the substituted compounds Ba(Mn(1-x)T(x))(2)As(2) (T = Cr, Fe, Co, Ni, Cu, Ru, Rh, Pd, Re, and Pt) and BaMn(2)(As(1-x)Sb(x))(2) out of Sn flux. Energy-dispersive x-ray analyses show that most of these elements do not substitute into the lattice in amounts greater than 0.5%. However, concentrations of 4.4%, similar to 10% and 2.6% were achieved for Cr, Fe, and Sb substitutions, respectively, and chi(T) and rho(T) data for these crystals are presented.