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Study of Morin transition in hematite (a- Fe₂O₃) nanoparticles by Mössbauer spectroscopy
Halder, Sajib
Halder, Sajib
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2020-07
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Electronic dissertations
Electronic dissertations
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Abstract
The change in magnetic properties of hematite (a- Fe₂O₃) nanoparticles were
investigated by observing the change of Morin transition fraction at different temperatures.
X-ray diffraction, transimission electron microscope (TEM), vibrating sample
magnetometer (VSM), and Mössbauer spectroscopy techniques applied to study the
magnetic and structural properties of the sample. According to the XRD results the
sample has a double phases with dominant hematite (a- Fe₂O₃) phase. The TEM
analysis confirmed the prepared nanoparticles have a large size distribution with average
diameter less than 20 nm. The Morin transition temperature of the sample was measured
by both the magnetization measurements and Mössbauer study. The zero-field cooled
(ZFC) and field-cooled (FC) magnetization measurements show the particles undergo a
magnetic phase transition from a weakly ferromagnetic to antiferromagnetic phase at
250 K. Room temperature Mössbauer spectra show the superparamagnetic behavior of the
materials where the magnetic moment fluctuates in all directions. Morin transition started
just below (285 K) the room temperature. The Morin transition was found strongly
temperature dependent and increased constantly with decreasing temperature. The
magnetic and structural changes with changing the Morin transition fraction revealed
important characterisitics about the sample. The Mössbauer spectra recorded at 140 K
and below showed complete Morin transition, which indicates the materials are strongly
antiferromagnetic. The average hyperfine magnetic field and isomer shift have similar
relationship and both continuously increased with decreasing temperature. The weighted
average Morin transition temperature for the sample obtained from Mössbauer studies is
265 15:8 K which is higher than the Morin transition found from the magnetization
measurements (250 K) measured by VSM.
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Thesis (M.S.)-- Wichita State University, College of Liberal Arts and Sciences, Dept. of Mathematics, Statistics, and Physics
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Wichita State University
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Copyright 2020 by Sajib Halder
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