Master of Science
Dr. Sanjay R. Mishra
Dr. Muhammad Shah Jahan
Dr. Jingbiao Cui
Shahabuddin, Mohammad. M.S. The University of Memphis. August/2014. Structural, Magnetic Properties and Mössbauer Analysis of Gd2Fe17-x-yNbxAly alloys. Major Professor: Sanjay R. Mishra, PhD.Binary rare-earth (R)-iron inter-metallic compounds with Th2Ni17 and Th2Zn17 structure have been extensively studied for their potential application as permanent magnets. The main drawbacks of these materials are low Curie temperature (Tc) and magnetic anisotropies. This thesis presents the effects of doubly substitution of iron atoms in R2Fe17 (R: Gd) with bigger non-magnetic Nb atoms and smaller non-magnetic Al atoms with changes in the structural and magnetic properties of the Gd2Fe17-x-yNbxAly (0 ≤ x ≤ 0.75 for Nb and 0 ≤ y ≤ 3.0 for Al) compounds. 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 Nb and Al content is observed in Gd2Fe17-x-yNb xAly. The Curie temperature (Tc) of Gd2Fe17-x-yNb xAly reaches a maximum value of 525K at Nb x = 0.75 and Al y = 2 substitution respectively. These observed values of Tc in Gd2Fe17-x-yNbxAly is 105 K higher than unsubstituted Gd2Fe17 (Tc = 420 K). This improvement in Tc is attributed to improved Fe-Fe exchange interaction due to unit cell volume expansion. The magnetization value of Gd2Fe17-yAly and Gd2Fe16.75-yNb0.25Aly decreased at the rate of 9.545 emu/gm and 9.244 emu/gm per Al atom respectively due to magnetic dilution. The room temperature Mössbauer analysis showed that the hyperfine field value decreased with Nb and Al doping due to decrease in magnetic moment of Fe atoms upon substitution. The isomer shift (IS) showed an increase with substitution due to an increase in volume expansion and decrease in s-electron density. Overall present study successfully shows improvement in Tc of co-doped Nb-Al Gd2Fe17-x-y NbxAly without much deterioration in magnetization. Thus the present Gd2Fe17-x-y NbxAly compound may find high temperature industrial applications.
Dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.
Shahabuddin, Mohammad, "Structural, Magnetic Properties and Mossbauer Analysis of Gd2Fe17-x-yNbxAly Compounds" (2014). Electronic Theses and Dissertations. 1025.