Abstract
Magnetite nanoparticles were synthesized by coprecipitation of reverse micelles in an aqueous phase. XRD, TEM and VSM results confirm the average particle size 9-10 nm. The FMR measurements were performed in zero-field-cooled (ZFC) and field-cooled (FC) protocol. Raikher and Morais models were used for interpreting the resonance field and linewidth results. A value of 2.3×10-2erg cm-2for intrinsic surface anisotropy constant is observed as per the Raikher model. The higher melting point of water leaves the magnetic particles with a more disordered distribution of anisotropy axes of particles even in FC measurements. The angular variation of resonance field differentiates the magnetic behavior of system in 4-40 K (region I), 70-200 K (region II) and 200-260 K (region III). The value of effective magnetic anisotropy constant varied from 4.7×104, 2.1×104to 0 erg cm-3through regions I, II to III. Linewidth analysis reveals that system undergoes spin-glass transition ~46 K. The fitting of linewidth data for region I and II indicate the presence of frozen and unfrozen surface spin states. Moreover, the role of applied magnetic field i.e. 1 T in field-cooled FMR spectra is reflected in interparticle distance parameter and magnitude of energy barriers related to the relaxation mechanisms. At 260 K fluid melts resulting in minimization of angular dependent anisotropy in resonance lines.
Original language | English |
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Pages (from-to) | 696-702 |
Number of pages | 7 |
Journal | Journal of Magnetism and Magnetic Materials |
Volume | 374 |
DOIs | |
Publication status | Published - 15 Jan 2015 |
Externally published | Yes |
Keywords
- Ferrofluid
- Ferromagnetic resonance
- Spin-glass transition
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics