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Title: Moessbauer effect: Study of disordered magnetic systems

This dissertation describes Moessbauer spectroscopy studies of two chemically disordered binary, crystalline alloys having the composition A{sub 1-x}B{sub x}. Both systems are random 3d Heisenberg ferromagnets. In each case both A and B atoms carry a magnetic moment. The first study concerns a Moessbauer absorber experiment on Fe{sub 1-x} V{sub x}, in which the disorder in the critical region is of the annealed random exchange type. To eliminate the effect of concentration inhomogeneity, the measurement of the critical exponent {beta} was done on the alloy with x = 0.125, where dT{sub C}/dx = 0, yielding {beta} = 0.362(8) over the reduced temperature range 1.4 {times} 10{sup {minus}3} < t < 4.88 {times} 10{sup {minus}1}. This result confirms the theoretical prediction that the annealed disorder is irrelevant to critical behavior in this case. As expected the critical exponent {beta} is consistent with the expectation for the 3d Heisenberg model as well as the measured exponent of pure Fe. The second study involves a Moessbauer source experiment on {sup 57} CoPd{sub 0.80}Co{sub 0.20}, in which disorder is of the quenched random exchange type perturbed by a very weak random anisotropy interaction. The critical exponent {beta} deduced over the range 1 {times} 10{supmore » {minus}2} < t < 2 {times} 10{sup {minus}1} is 0.385(20), and is consistent with the theoretical prediction for quenched disordered 3d Heisenberg systems: the disorder is irrelevant to the critical behavior. However, because of the restricted range of reduced temperature, the result is insufficiently asymptotic to serve as a conclusive test of the theory. Outside the critical region the distribution of Fe{sup 57} hyperfine field in Pd{sub 0.80}Co{sub 0.20} is observed to have an anomalous temperature dependence characterized by a linear increase in the width of the field distribution for T/T{sub C} {ge} 0.6.« less
Authors:
Publication Date:
OSTI Identifier:
5944556
Resource Type:
Miscellaneous
Resource Relation:
Other Information: Thesis (Ph. D.)
Publisher:
Worcester, MA (US); Clark Univ.
Research Org:
Clark Univ., Worcester, MA (USA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; COBALT ALLOYS; MAGNETIC PROPERTIES; ORDER-DISORDER TRANSFORMATIONS; PALLADIUM ALLOYS; ANISOTROPY; BINARY ALLOY SYSTEMS; COBALT 57; FERROMAGNETIC MATERIALS; HEISENBERG MODEL; MAGNETIC MATERIALS; MAGNETIC MOMENTS; MOESSBAUER EFFECT; TEMPERATURE DEPENDENCE; ALLOY SYSTEMS; ALLOYS; BETA DECAY RADIOISOTOPES; COBALT ISOTOPES; CRYSTAL MODELS; DAYS LIVING RADIOISOTOPES; ELECTRON CAPTURE RADIOISOTOPES; INTERMEDIATE MASS NUCLEI; ISOTOPES; MATERIALS; MATHEMATICAL MODELS; NUCLEI; ODD-EVEN NUCLEI; PHASE TRANSFORMATIONS; PHYSICAL PROPERTIES; PLATINUM METAL ALLOYS; RADIOISOTOPES 360102* -- Metals & Alloys-- Structure & Phase Studies; 360104 -- Metals & Alloys-- Physical Properties; 656002 -- Condensed Matter Physics-- General Techniques in Condensed Matter-- (1987-)