Moessbauer effect: Study of disordered magnetic systems

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1989

OSTI ID:5944556

Chang, Xiao Sha

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{sup {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.

• Research Organization: Clark Univ., Worcester, MA (USA)
• OSTI ID: 5944556
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals &amp; Alloys-- Structure &amp; Phase Studies
360104 -- Metals &amp; Alloys-- Physical Properties
656002 -- Condensed Matter Physics-- General Techniques in Condensed Matter-- (1987-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALLOY SYSTEMS
ALLOYS
ANISOTROPY
BETA DECAY RADIOISOTOPES
BINARY ALLOY SYSTEMS
COBALT 57
COBALT ALLOYS
COBALT ISOTOPES
CRYSTAL MODELS
DAYS LIVING RADIOISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
FERROMAGNETIC MATERIALS
HEISENBERG MODEL
INTERMEDIATE MASS NUCLEI
ISOTOPES
MAGNETIC MATERIALS
MAGNETIC MOMENTS
MAGNETIC PROPERTIES
MATERIALS
MATHEMATICAL MODELS
MOESSBAUER EFFECT
NUCLEI
ODD-EVEN NUCLEI
ORDER-DISORDER TRANSFORMATIONS
PALLADIUM ALLOYS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
PLATINUM METAL ALLOYS
RADIOISOTOPES
TEMPERATURE DEPENDENCE