Search for magnets with properties intermediate between Nd-Fe-B and ferrite
Başlık çevirisi mevcut değil.
- Tez No: 403394
- Danışmanlar: Prof. J. M. D. COEY
- Tez Türü: Doktora
- Konular: Fizik ve Fizik Mühendisliği, Physics and Physics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2016
- Dil: İngilizce
- Üniversite: Unıversıty Of Dublın (trınıty College)
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
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Özet (Çeviri)
The rare earth elements neodymium, samarium, terbium and dysprosium are predominantly mined in China (>95%) there wild prices fluctuations in 2011 as a result of Chinese government policies undermined confidence in the security of rare earth supplies. There is a need for a new magnet with little or no rare earth to fill the magnet gap between ferrite and Nd-Fe-B, to be used for intermediate energy applications. In this thesis, a novel magnet aimed at intermediate energy applications is investigated (100 (BH)max 200 kJ/m3). Two approaches are used in order to fill this gap which are (1) atomic substitutions in known uniaxial materials with high Curie temperature with a view to reducing materiel's cost or improving process ability (2) finding a new compounds from Heusler family. Chapter 1 is an introduction focused on the evolution of magnets over the centuries and the intrinsic and extrinsic requirements for a new gap magnet. The requirements are high saturation magnetization (Ms), Curie temperature (TC), anisotropy constant (K) , coercivity (Hc), demagnetizing/stray field (Hd) and maximum energy product ((BH)max) . All these terms are explained in detail. Chapter 2 is about experimental procedures which are used in this thesis which are mechanical alloying, ball milling, X-ray diffraction, advance microscopy (SEM and TEM), SQUID magnetometry and Mössbauer spectroscopy. In Chapter 3, Fe-doped La(Co5-xFex) and La2(Co7-xFex) with 0 x <1 were prepared by ball milling. LaCo5 and La2Co7 are good candidate as La is surplus and substitution of iron for cobalt on 3g site would increase the saturation magnetization while it will decrease its price. In order to achieve the optimum grain size for a high coercivity the ball to powder ratio was varied. Powder samples were annealed from 700 to 950°C for 1 to 10 minutes under high vacuum in order to find the magnetically optimum condition. The crystallographic, magnetic and microstructure properties of bulk and of powders of these compounds were investigated in detail. Further the 57Fe Mössbauer spectrum is also analyzed for LaCo4Fe1. Chapter 4 is about the optimization of the magnetic properties of nanostructured Y-Co-Fe alloys for use as permanent magnets. First, the magnetic and crystallographic properties were analyzed for samples which were rapid thermal annealed under argon (800°C and 1050°C for 1–5 min) . Later, the magnetic hysteresis of ball-milled YCo5-xFex powder with 0 x 0.5 was optimized by controlling the temperature and time for rapid annealing under vacuum (800 and 850°C for 2-3 min) and argon (800°C only 1-3 min). The magnetic properties were investigated for these powders which were embedded in epoxy, with some of these aligned under 5 T. The microstructure and crystalographic properties were investigated as well. Several ballmilled YCo4:8Fe0:2 powders were prepared in order to investigate the reproduciblity. Some batches were used to press solid sample with or without the presence of magnetic field and with pre- or post-vacuum annealing procedure. Moreover, polymer bonded and directional solidified YCo4:8Fe0:2 were investigated. A high-throughput approach with computational screening has the potential to identify those alloys that have a sufficiently high magnetocrystalline anisotropy, which show tetragonal distortion and meet the criterion of being sufficiently low-cost for permanent magnet applications. In Chapter 5, thirteen new candidate magnetic Heusler alloys areCo2MnTi, Fe2CuGa, Ni2FeGa, Mn2PtPd, Mn2PtCo;Mn2PtV, Rh2VSn, Rh2FeSn, Fe2MoSi, Co2NiSi, Mn2CoCr, Fe2CoB and Mn2PtRh which were identified by Prof. Sanvito's group. All these alloys have been prepared in order to investigate new possible rare-earth-free magnetic materials, which have a uniaxial crystal structure and anisotropy. In this chapter the results of the ab-initio calculations and magnetic and crystallographic characterization of these alloys are compared with the experimental results. Chapter 6 is about the Mn-Ga based alloys which are currently of the focus of two interconnected topics in magnetism; permanent magnets and spintronics. In particular, Mn8Ga5 is an interesting binary compound which often appears as a secondary phase that can significantly influence the formation and magnetic properties of the main MnGa or Mn3Ga2 with tetragonal L10 phase. In this chapter, the structural and magnetic properties of the binary Mn8Ga5 compound are investigated experimentally and by using density functional theory for the first time. Ab- initio calculations are performed by Dr. Z. Gercsi. The magnetic and structural properties of binary Mn8Ga5 were investigated under different annealing conditions in an effort to obtain the s1,s2 and s3 phases which were defined in a revised Mn-Ga phase diagram based on differential scanning calorimetry. Finally, in chapter 7, the results were summarized and future work is described.
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