Type of Document Dissertation Author Kangas, Michael James URN etd-08272012-123825 Title On the Synthesis, Characterization, and Magnetization of Ln-M-X (Ln = Lanthanide; M = Ti-Cr, Cu, Mo, Pd; X = Al, Ga) Intermetallics Degree Doctor of Philosophy (Ph.D.) Department Chemistry Advisory Committee
Advisor Name Title Chan, Julia Y Committee Chair Stadler, Shane Committee Member Stanley, George G Committee Member Young, David P Committee Member Madden, James J Dean's Representative Keywords
- heavy fermion
- flux growth
Date of Defense 2012-08-02 Availability restricted AbstractThe focus of the research presented herein was to grow single crystals of Ln-M-X (Ln = lanthanide; M = Ti-Cr, Cu, Mo, Pd; X = Al, Ga) intermetallic compounds and to characterize their crystal structures and physical properties. Overall, the flux growth technique facilitated a detailed analysis of previously known structure-types (LnM2Al20 (Ln = La, Ce, Pr, Yb; M = Ti, V, Cr), Ln6M4Al43 (Ln = Gd, Yb; M = Cr, Mo), and Yb2Pd3Ga9), as well as the synthesis and characterization of new compounds (LnCrxGa3 (Ln = Ho, Er; x ~ 0.13), YbCr2Al20-xFex (x ~ 0.2), Ln(Cu,Al,Ga)13-x, and Ln2PdGa12 (Ln = Pr, Nd, Sm)).
LnCrxGa3 (Ln = Ho, Er) adopt a stuffed variant of the AuCu3 structure-type rather than the related Y4PdGa12 structure-type which is adopted by the latter transition metals. Like the related Ln4MGa12 compounds, both analogues exhibit positive magnetoresistance, with ErCrxGa3 reaching ~25% at H = 9 T.
After characterizing a number of LnM2Al20 (Ln = La, Ce, Pr, Yb; M = Ti, V, Cr) compounds, Fe was introduced to determine if it would influence the physical properties and to better understand the stability of the CeCr2Al20 structure-type. Mössbauer spectroscopy results for YbCr2FexAl20-x indicate that Fe atoms occupy two crystallographic sites, and X ray diffraction refinements suggest that the Fe atoms occupy the Al1 and Al2 sites rather than the Cr site. These results are consistent with LnM2Al20 compounds only forming for early transition metals.
Single crystals of Yb6M4Al43 are non-magnetic consistent with divalent Yb, which contrasts with previously reports. Gd6M4Al43 (M = Ce, Mo, W) appear to order antiferromagnetically below 20 K with positive Weiss temperatures, suggesting that the magnetic structures of these materials are complex.
Single crystals of Ln2PdGa12 order antiferromagnetically at 18, 7.5, and 7.5 K, respectively, and heat capacity measurements indicate that Pr2PdGa12 may be a new Pr containing heavy fermion compound.
Single crystal neutron diffraction experiments were successfully carried out on NaZn13 type Ln(Cu,Al,Ga)13-x, including Eu(Cu,Al,Ga)13-x, to understand the site occupancies and disorder, and it was found that Cu partially occupies the 8b site while the 96i site is populated with Al, Cu, and Ga.
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