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Title:	Microstructural, optical and magnetic properties of yttrium iron garnets nano-films co-substituted with erbium-terbium and erbium-cerium ions
Authors:	Suleiman Musa .M. Elhamali (P76776)
Supervisor:	Noor Baayah Ibrahim, Assoc. Prof. Dr.
Keywords:	Microwaves Ferrite Ferrimagnetism Universiti Kebangsaan Malaysia -- Dissertations Dissertations, Academic -- Malaysia
Issue Date:	8-Jan-2018
Description:	The large Faraday rotation angle (θF) of Tb-YIG and Ce-YIG is a key property that makes them suitable candidates for the devices that require a non-reciprocal operation. However, it is difficult to introduce a large amount of Tb3+or Ce3+ into the YIG due to their large ionic radius compared to the Y3+ ion. Nevertheless, the lattice distortion may be relaxed by adding Er3+ ions with smaller ionic radius and high magnetic moment, without the degradation of Faraday rotation. In this study, a series of YIG, Tb0.2 Ery Y2.8-y Fe5 O12 (0 ≤ y ≤ 2.8) and Ce0.2 Ery Y2.8-y Fe5 O12 (0 ≤ y ≤ 1.0) nanocrystalline films were prepared by a sol-gel method. The effect of different annealing environments, i.e. air, oxygen and argon on the nanostructure, surface morphology, optical and magnetic properties were investigated. All films were deposited on quartz substrates and crystallised at 900 °C. The X-ray diffractometer (XRD) results revealed the single-phase structure of YIG films, regardless of the atmospheres. As more Er3+ introduced into Tb0.2 Ery Y2.8-y Fe5 O12 (y >1.0), the single-phase structure of Er3 Fe5 O12 was obtained, as confirmed by IR spectra. The increase in lattice constant was observed at low Er content (y ≤ 1.4) for the films annealed in air. This attributed to the formation of Fe2+ ions, as confirmed by X-ray Photoelectron Spectroscopy (XPS). The surface morphology, obtained using field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM), showed nanograins with the void formation, a good adhesion of the film to the substrate and a smooth surface for the films annealed in O2 gas. The optical transparency increased from 65% for Tb: YIG to 96 % for Tb0.2 Er0.4 Y2.4 Fe5 O12 films annealed in air. For films annealed in O2 and Ar gas, it increased from 83 % and 80 % at y=0 to 98 % at y=0.8, respectively in the near-IR region. Higher saturation magnetization, 220 emu/cm3 was obtained from Tb0.2 Er1 Y1.8 Fe5 O12 films annealed in air, whereas the lowest value, 30 emu/cm3 was obtained from Tb0.2 Er2.8 Fe5 O12 annealed in Ar gas. All films showed enhancement in the coercivity field, Hc, regardless of the annealing surrounding. The highest value (87.5 Oe) was obtained from Tb0.2 Er2.8 Fe5 O12 film annealed in Ar gas. The YIG and TbErIG films show a phase transition from ferromagnetic to paramagnetic at Curie temperature, Tc = 556 K, and 557.3 K, respectively. For Ce0.2 Ery Y2.8-y Fe5 O12 (y=0-1.0) films, the oxygen annealing produced more crystallisation compared to those annealed in air / Ar. A single phase YIG structure was revealed by XRD and confirmed by FTIR and Raman spectra. The lattice constant decreased linearly with Er content. Energy Dispersive X-ray (EDX) confirmed the presence of Ce, Er, Y, Fe, and O elements. The optical transmittance increased from 88% at y=0.0 to 99.8% at y=0.4 and y=0.8 in the wavelength range 1000-1400 nm. However, as more erbium ions were introduced, the saturation magnetisation decreased and the coercivity field increased. According to the obtained results, a new Tb0.2 Ery Y2.8-y Fe5 O12 and Ce0.2 Ery Y2.8-y Fe5 O12 nanoferrite films can be applied in a magneto-optical isolator and circulator.,Ph.D.
Pages:	194
Call Number:	TK7870.E434 2018 tesis
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Science and Technology / Fakulti Sains dan Teknologi

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