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Superconductivity, spin-glass properties, and ferromagnetism in amorphous La-Gd-Au alloys


Poon, Siu-Joe (1978) Superconductivity, spin-glass properties, and ferromagnetism in amorphous La-Gd-Au alloys. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/s0jp-gw13.


The superconducting and magnetic properties of splat cooled amorphous alloys of composition (La100-xGdx)80Au20 (0 ≤ x ≤ 100) have been studied. The La80Au20 alloys are ideal type II super-conductors (critical temperature Tc = 3.5° K ). The concentration range (x less than 1) where superconductivity and spin-glass freezing n1ight coexist has been studied in detail. The spin-glass alloys (0 less than x less than 70) exhibit susceptibility maxima and thermomagnetic history effects. In the absence of complications due to crystal field and enhanced matrix effects, a phenomenological model is proposed in which the magnetic clusters are treated as single spin entities interacting via random forces using the molecular field approach. The fundamental parameters (such as the strength of the forces and the size of clusters) can be deduced from magnetization measurements. The remanent magnetization is shown to arise from an interplay of the RKKY and dipolar forces. Magnetoresistivity results are found to be consistent with the aforementioned picture. The nature of magnetic interactions in an amorphous matrix is also discussed. The moment per Gd atom (7µB) is found to be constant and close to that of the crystalline value throughout the concentration range investigated. Finally, a detail study is made of the critical phenomena and magnetic properties of the amorphous ferromagnet: Gd80Au20. The results are compared with recent theories on amorphous magnetism.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Applied Physics
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Applied Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Duwez, Pol E.
Thesis Committee:
  • Unknown, Unknown
Defense Date:1 August 1977
Record Number:CaltechTHESIS:07182014-144716507
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8569
Deposited By: Benjamin Perez
Deposited On:21 Jul 2014 14:32
Last Modified:09 Nov 2022 19:20

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