Crystal Growth and an Investigation of Structural Stability: Synthesis, Structure, and Physical Properties of Yb(Mn,M)xAl12-x (M = Fe, Ru; x < 2.5) and LnMnxGa3 (Ln = Ho-Tm; x < 0.15)

Abstract

The contents of this dissertation describe the crystal growth, crystal structures, and physical properties of ternary intermetallic aluminides and gallides. These compounds are grown in an effort to determine how controlling reaction ratios using the flux growth method can impact chemical structure and physical properties. Three specific examples are given where slight changes in reaction ratios leads to crystalline products that adopt various structure types. LnMn2+xAl10-x (Ln = Gd, Yb) crystals adopt the CaCr2Al10 and ThMn12 structure types. We compare LnMn2+xAl10-x compounds adopting the CaCr2Al10 and ThMn12 structure types, and outline synthesis methods to obtain each polymorph. Magnetic susceptibility measurements show paramagnetic behavior down to 3 K for both CaCr2Al10- and ThMn12-type compounds, with observed magnetic moments of 1.3 B for compounds adopting the CaCr2Al10 structure type to 4.2 B for those adopting the ThMn12 structure type. Compounds of both structure type exhibit metallic resistivity, with upturns at low temperature attributed to Kondo scattering. Single crystals of Yb(Mn,M)xAl12-x (M = Fe, Ru; x ≤ 2.5) adopt three structure types, the ThMn12 structure type, and two structural derivatives, the CaCr2Al10 structure type and the YbFe2Al10 structure type, depending on the starting amount of Mn relative to M. We outline the synthetic parameters used to obtain products in all three structure types and specifically address how stabilizing products in one structure type over another is a function of Mn:M reaction ratios. Yb(Mn,Fe)xAl12-x compounds exhibit paramagnetic behavior down to 2 K, as well as metallic resistivity down to ~ 50 K. Below 50 K, Yb(Mn,Fe)xAl12-x compounds exhibit upturns in resistivity that indicate the onset of Kondo interactions. Finally, single crystals of LnMnxGa3 (Ln = Ho-Tm; 0 < x < 0.15) crystallize in a variant of the AuCu3 structure type (space group Pm3 ̅m) where Mn partially occupies the body center of the unit cell. These “stuffed” AuCu3-type LnMnxGa3 compounds are presented as intermediates between AuCu3- and Y4PdGa12-type compounds. HoMnxGa3 and ErMnxGa3 order antiferromagnetically, with effective moments decreasing as a function of Mn concentration and TN increasing as a function of Mn concentration. TmGa3 orders antiferromagnetically at ~ 4.2 K while TmMnxGa3 (x > 0) are paramagnetic down to 1.8 K.