Vikas Nandwana, Ph.D.
http://hdl.handle.net/10106/5067
Doctoral Student2024-03-28T17:07:14ZRapid thermal annealing of FePt nanoparticles
http://hdl.handle.net/10106/5102
Rapid thermal annealing of FePt nanoparticles
Nandwana, Vikas; Yano, Kazuaki; Poudyal, Narayan; Rong, Chuan-Bing; Liu, J. Ping
We report a systematic study on rapid thermal annealing (RTA) of FePt nanoparticles. FePt particles with an average size of 8 nm were synthesized by a chemical solution method, and then annealed using RTA and conventional furnace annealing (FA). It was observed that FePt nanoparticles can be transformed from disordered A1 phase to ordered L10 phase at 650 °C for 10 s using RTA, which is much shorter than the time needed for FA. The transmission electron microscopy and x-ray diffraction studies have revealed that the particle agglomeration and grain growth in the RTA treated samples are much less than in the FA treated samples. A linear correlation between the coercivity and the square root of the treatment time was observed in the RTA treated samples, which implies that the phase transition is related to atomic diffusion of Fe atoms from Fe-rich shells into the Pt-rich cores.
2008-07-01T00:00:00ZHigh thermal stability of carbon-coated L10-FePt nanoparticles prepared by salt-matrix annealing
http://hdl.handle.net/10106/5101
High thermal stability of carbon-coated L10-FePt nanoparticles prepared by salt-matrix annealing
Nandwana, Vikas; Rong, Chuan-Bing; Poudyal, Narayan; Chaubey, Girija S.; Liu, Yuzi; Wu, Y.Q.; Kramer, M.J.; Kozlov, M.E.; Baughman, Ray H.; Liu, J. Ping
Monodisperse L10-FePt nanoparticles with size ranging from 3 to 8 nm were prepared by the salt-matrix annealing method. It was observed that the annealed particles have high thermal stability—no sintering occurred even when the particles were heated at 1100 °C for an hour. This high thermal stability resulted from carbon coating of the particles during salt-matrix annealing as consequence of decomposition of surfactants.
2008-01-01T00:00:00ZStructural phase transition and ferromagnetism in monodisperse 3 nm FePt particles
http://hdl.handle.net/10106/5084
Structural phase transition and ferromagnetism in monodisperse 3 nm FePt particles
Nandwana, Vikas; Rong, Chuan-Bing; Chaubey, Girija S.; Skomski, R; Wu, Y.Q.; Kramer, M.J.; Liu, J. Ping
FePt nanoparticles with a size of 3 nm and thermally stable room-temperature ferromagnetism are investigated. The monodisperse nanoparticles were prepared by chemical synthesis and a salt-matrix annealing technique. Structural and magnetic characterizations confirmed the phase transition from the disordered face-centered cubic structure to the L10 structure with the chemical ordering parameter of 0.62±0.05. Analysis in blocking temperature and fitting of temperature dependence of switching field reveals that the transformed 3 nm nanoparticles have a magnetic anisotropy constant of (2.8±0.2)×106 J/m3, smaller than those for the bigger particles and the fully ordered L10 bulk phase.
2007-01-01T00:00:00ZBulk FePt-based nanocomposite magnets with enhanced exchange coupling
http://hdl.handle.net/10106/5083
Bulk FePt-based nanocomposite magnets with enhanced exchange coupling
Nandwana, Vikas; Liu, J. Ping; Poudyal, Narayan; Rong, Chuan-Bing; Kozlov, Mikhail E.; Baughman, Ray H.; Ding, Yong; Wang, Zhong Lin
High density bulk FePt/Fe3Pt nanocomposite magnets have been prepared by high-pressure warm compaction of chemically synthesized FePt and Fe3O4 nanoparticles. It is found that the density increases with the compaction pressure and temperature. Density of the bulk samples up to 95% theoretical value has been obtained while the nanostructured morphology is retained. It is also observed that a high pressure expedites the FePt phase transition from the disordered face-centered-cubic structure to the L10 structure, leading to the phase transition temperature in the compacts one hundred degrees lower than usual. This phase transition in turn facilitates the consolidation of the compacts. Magnetic characterizations showed that interphase exchange coupling is enhanced upon the compaction. Post-annealing of the compacts results in further improved magnetic performance of the compacts owing to interface modification. Energy products up to 16.3 MG Oe of the isotropic bulk nanocomposite magnets have been achieved, which is significantly higher than the theoretical limit for fully dense single-phase FePt magnets.
2007-01-01T00:00:00Z