Degree Type

Thesis

Date of Award

1-1-2002

Degree Name

Master of Science

Department

Materials Science and Engineering

Major

Materials Science and Engineering

Abstract

A study of a series of Dy5(Si[Subscript x]Ge[Subscript 1-x])4 alloys using dc and ac magnetic susceptibility, magnetization, heat capacity, and x-ray powder diffraction techniques revealed that the variation of the magnetic properties and crystal structures with composition is similar to that observed in the Gd5(Si[Subscript x]Ge[Subscript 1-x])4 system, except that the magnetic ordering temperatures are lower. The magnetic phase transition temperatures vary from [Difference symbol] 46K (Dy5Ge4) to [Difference symbol] 137K (Dy5Si4). The intermediate ternary phase Dy5Si3Ge undergoes a first order magnetic phase transition at [Difference symbol] 65K. The value of magnetic entropy change for this composition is quite large (-34J/kgK for magnetic field change from 0 to 50kOe), compared to the values for the two end members (-7 J/kgK for Dy5Ge4 and -12.5J/kgK for Dy5Si4). The magnetization and ac susceptibility measurements showed that alloys with monoclinic crystal structure have a non-collinear ordering of the magnetic moments at low temperatures. The alloy Dy5Si3Ge appears to exhibit a spin-glass transformation below the magnetic phase transition at 65K. Also a series of critical fields are observed at low temperature during magnetization vs magnetic field measurements in all of the Dy5(Si[Subscript x]Ge[Subscript 1-x])4 alloys regardless type of crystal structure. The Dy5(Si[Subscript x]Ge[Subscript 1-x])4 alloys, where 0.67[Less than or equal to]x[Less than or equal to]l, may be useful magnetic refrigerant materials in the [Difference symbol]50 to [Difference symbol]160K temperature range.

DOI

https://doi.org/10.31274/rtd-20200723-5

Copyright Owner

Vitaliy Vladislavovich Ivchenko

Language

en

OCLC Number

51044216

File Format

application/pdf

File Size

113 pages

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