Exploration of New Ternary Gallides and Investigation of Their Structure-Property Relationships
This dissertation focuses on the investigation of new ternary intermetallic gallides, which may exhibit exotic physical properties such as heavy-fermion behavior, large magnetoresistance, and even superconductivity. In particular, the Ln-Cu-Ga (Ln = lanthanides) system has been systematically investigated by changing a reaction ratio and/or using a different temperature profile to optimize desired phases. Single crystals of Ln2MGa12 (Ln = La, Ce; M = Ni, Cu) have been synthesized using Ga flux and compared to their Pd analogues. Interestingly, Ce2MGa12 (M = Ni, Cu) show enhanced Sommerfeld coefficient of ¡Ö 191 mJmol-1K-2 and ¡Ö 69 mJmol-1K-2 for Ni and Cu compounds, respectively. Three different structure types such as Ln(Cu,Ga)13 (Ln = La¨CNd, Eu), SmCu4Ga8, and Ln(Cu,Ga)12 (Ln = Y, Gd¨CEr, Yb) have been synthesized by increasing Cu concentration. A large positive magnetoresistance up to 154 % at a field of 9 T is observed for Pr(Cu,Ga)13. Most interestingly, Pr(Cu,Ga)13 shows T2 temperature-dependent resistivity and satisfies Kadowaki-Woods relation, which is indicative of heavy-fermion behavior. The ordered SmCu4Ga8 grown by flux method has been compared to its isostructural disordered analogue, SmCu4.1Ga6.9. Ln(Cu,Ga)12 (Ln = Gd¨CEr) compounds order antiferromagnetically at 12.5 K, 13.5 K, 6.7 K, and 3.4 K for Gd-, Tb-, Dy-, and Er-analogues, respectively. Ln4MGa12 (Ln = Dy¨CEr; M = Pd, Pt) have been grown from Ga flux. Magnetic measurements show that Dy4PdGa12 and Er4PdGa12 are antiferromagnetic with transitions at TN = 10 K and 5.2 K, respectively, while Ho4PdGa12 does not show any magnetic ordering down to 2 K. Ln4PtGa12 (Ln = Dy¨CEr) order antiferromagnetically at TN = 9.8 K, 3.6 K and 5.1 K for Dy-, Ho-, and Er-analogues, respectively. The electrical resistivity data show metallic behavior. Large positive magnetoresistance is shown up to 900 % at 3 K and 9 T for the Ho4PtGa12 analogue. Single crystals of LnAgyX4-y (Ln = La, Ce; X = Al, Ga; y ¡Ö 0.72) have been synthesized by aluminum or gallium flux. These compounds show an occupational disorder for Ag sites. CeAg0.72Al3.28 and CeAg0.67Ga3.33 are metallic, and magnetic measurements indicate that both order ferromagnetically near 3 K.
Advisor:Andrew W. Maverick; George G. Stanley; David P. Young; Julia Y. Chan; Roger A. Laine
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Date of Publication:11/13/2008