Electronic Theses and Dissertations

Identifier

926

Date

2013

Document Type

Thesis

Degree Name

Master of Science

Major

Physics

Concentration

Materials Science

Committee Chair

Sanjay R Mishra

Committee Member

M. Shah Jahan

Committee Member

Donald R Franceschetti

Abstract

The main drawbacks of rare earth intermetallic magnets are their low Curie temperature (Tc) and magnetic anisotropies. Many efforts have been made to improve these properties of R2Fe17 permanent magnets by doping metals and non-metals atom for Fe or inserting interstitials atoms in R2Fe17 lattice. In the present work, the effect of substitution of non-magnetic atom, Zr for Fe in Dy2Fe17-xZrx and Dy2Fe16Ga1-xZrx and magnetic atoms in Gd2Fe16Ga0.5TM0.5 (TM = Cr, Mn, Co, Ni, Cu, Zn) are studied. The structural and magnetic properties of these compounds have been studied via x-ray diffraction, vibrating sample magnetometer (VSM) and 57Fe Mössbauer Spectroscopy. An increase in unit cell volume with the increase in Zr content is observed in Dy2Fe17-xZrx and Dy2Fe16Ga1-xZrx but no systematic variation in the unit cell volume is observed with transition metal doping. The Curie temperature (Tc) of Dy2Fe17-xZrx and Dy2Fe16Ga1-xZrx reaches a maximum value of 510 K at x = 0.75 and 505.1 K at x = 0.5 Zr substitution respectively. These observed values of Tc in Dy2Fe16.25Zr0.75 and Dy2Fe16Ga0.5Zr0.5 are 102 K and 97 K higher than their Dy2Fe17 (Tc = 408 K) . This improvement in Tc is attributed to improved Fe-Fe exchange interaction due to unit cell volume expansion. The achieved Curie temperatures of transition metal doped intermetallic are also better than Gd2Fe17 and Gd2Fe16Ga1. The magnetization value of Dy2Fe17-xZrx and Dy2Fe16Ga1-xZrx decreased at the rate of 10.99 emu/gm and 9.244 emu/gm per Zr atom respectively. The difference in magnetization values between Zr and Ga-Zr doped samples may be attributed to the variation in d-electron density and magnetovolume effect. The room temperature Mössbauer analysis showed decrease in average hyperfine field and increase in isomer shift with Zr doping for Dy2Fe17-xZrx and Dy2Fe16Ga1-xZrx. But the variation in average hyperfine field in Gd2Fe16Ga0.5TM0.5 was observed to depend on the magnetic nature of TM element and the unit cell volume. However isomer shift showed continuous increase with the increase increase in atomic number of TM atoms.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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