Degree Type

Dissertation

Date of Award

1987

Degree Name

Doctor of Philosophy

Department

Physics and Astronomy

Abstract

A focussed study on the effect of transition metal substitution for Fe in the compounds Lu[subscript]2(Fe[subscript]1-xT[subscript]x)[subscript]3Si[subscript]5 (Where T = Cr, Mn, Co, Ni Cu, and Ru) is reported. The effect of these transition metals on the superconducting transition temperature shows that Cr, Co, Ni and Ru all act as non-magnetic impurities. By fitting the experimental data T[subscript]c/T[subscript]co to Kaiser's equation, a good agreement with Kaiser's theory is obtained. The rate of suppression due to Co substitution is similar to that of Ru. Superconductivity persists ( T[subscript]c = 0.49K) even when 10 at.% Co is substituted for Fe. In contrast, Mn and Cu act as magnetic impurities and suppress T[subscript]c in a way described by the theory of Abrikosov and Gor'kov;The molar magnetic susceptibility of Lu[subscript]2Fe[subscript]3Si[subscript]5 does not follow a Curie-Weiss law, but rather increases slightly as temperature increases. The addition of Ru lowers the value of [chi] (T), but the overall shape of [chi] (T) is unchanged. In contrast, the substitution of the nominally magnetic transition metals Cr, Mn, Co and Ni for Fe causes [chi] (T) to become more Curie-Weiss like. The magnetic susceptibility of the compound Lu[subscript]2Co[subscript]3Si[subscript]5 follows the Curie-Weiss law, while that of the compound Lu[subscript]2Ru[subscript]3Si[subscript]5 is diamagnetic;The electrical resistivity [rho] (T) of the compound Lu[subscript]2Fe[subscript]3Si[subscript]5 is approximately quadratic in T at temperatures below 50 K and proportional to lnT at temperature above 100 K;The low temperature heat capacity data of the Co- and Ru-containing samples are similar and both fit to equations [gamma][subscript]sT+[beta][subscript]sT[superscript]3 below T[subscript]c and [gamma][subscript]nT+[beta][subscript]nT[superscript]3+[alpha][subscript]nT[superscript]5 above T[subscript]c in agreement with the heat capacity measurement by C. B. Vining for the compound Lu[subscript]2Fe[subscript]3Si[subscript]5. Increasing the concentration of Co or Ru lowers the Debye temperature and the electronic density of states at the Fermi level of the compounds and enhances the linear term in the superconducting state heat capacity. The reduced specific heat jump between C[subscript]s and C[subscript]n at T[subscript]c follows neither the BCS prediction nor the Abrikosov and Gor'kov's theory;All of the data in this investigation show that the strong covalent bonding between the iron and the silicon atoms in this complex crystal structure is related directly to the unusual behavior of these 3d transition metals in the compounds Lu[subscript]2(Fe[subscript]1-xT[subscript]x)[subscript]3Si[subscript]5. ftn * DOE Report IS-T-1280. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.

DOI

https://doi.org/10.31274/rtd-180813-12332

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Youwen Xu

Language

en

Proquest ID

AAI8721942

File Format

application/pdf

File Size

100 pages

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