Magnetic and magnetoelastic properties of a series of M-substituted cobalt ferrites, CoMxFe2-xO4 (M=Mn, Cr, Ga; x=0.0 to 0.8) and Ge-substituted cobalt ferrites Co1+xGexFe 2-2xO4 (x=0.0 to 0.6) have been investigated. The Curie temperature TC and hysteresis properties were found to vary with substitution content x, which indicates that exchange and anisotropy energies changed as a result of substitution of those cations for Fe. The maximum magnitude of magnetostriction decreased monotonically with increase in substitution contents x over the range x=0.0 to 0.8. However, the rate in change of magnetostriction with applied magnetic field (dλ/dH) showed a maximum value of 5.7 × 10-9 A-1m at x=0.1 Ge sample, which is the highest value among recently reported cobalt ferrite based materials. The slope of magnetostriction with applied field dλ/dH is one of the most important properties for stress sensor applications because it determines the sensitivity of magnetic induction to stress (dB/dσ). The results of Ga- and Ge-substituted cobalt ferrite were compared with those of Mn- and Cr-substituted cobalt ferrites, and it was found that the effect of the substituted contents x on magnetic and magnetoelastic properties was dependent on the ionic distribution between two possible interstice sites within the spinel structure: Mn3+ and Cr3+ prefer the octahedral sites, whereas Ga3+ and Ge4+ prefer the tetrahedral sites. Temperature dependence of the absolute magnitude of the magnetic anisotropy constant |K1| of Ga-substituted cobalt ferrites CoGaxFe 2-xO4 (x=0.0 to 0.8) was investigated based on the law of approach to saturation and the results were compared with those of magnetostriction measured at the same temperatures. Based on the results, it was considered that there was a change in sign of K1 around 200 K for Ga-substituted cobalt ferrites. Comparison of the results between Ga- and Ge-substituted cobalt ferrites showed that substitution of Ge4+ ions for Fe made more pronounced effects on magnetic and magnetoelastic properties at room temperature than that of Ga3+ ions. Especially the enhanced value in dλ/dH by Ge-substitution suggests that adjusting Ge content substituted into cobalt ferrite can be a promising route for controlling critical magnetic properties of the material for practical sensor applications.
|Advisor:||Jiles, David C.|
|School:||Iowa State University|
|Department:||Materials Science and Engineering|
|School Location:||United States -- Iowa|
|Source:||DAI-B 68/10, Dissertation Abstracts International|
|Keywords:||Chromium, Cobalt ferrites, Gallium, Germanium, Magnetoelastic, Magnetomechanical sensor, Magnetostriction, Manganese|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be