Impact of Chemical and Morphological Changes on the Phase Stability of Magnetic Materials

Skelland, C

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dc.contributor	Hrkac, Gino
dc.contributor	Hicken, Robert
dc.creator	Skelland, C
dc.date	2022-08-25T15:10:24Z
dc.date	2022-08-22
dc.date	2022-08-25T11:49:40Z
dc.date	2022-08-25T15:10:24Z
dc.date.accessioned	2023-02-23T12:15:43Z
dc.date.available	2023-02-23T12:15:43Z
dc.identifier	EP/P015409/1
dc.identifier	http://hdl.handle.net/10871/130532
dc.identifier.uri	http://localhost:8080/xmlui/handle/CUHPOERS/258592
dc.description	Permanent magnetic materials are of fundamental importance to the modern world, utilised in fields as broad as computers, cars, and MRI machines. Their importance is set to increase as the world move towards sustainable energy and away from fossil fuels. A seamless switch requires an increase in magnet production, and an improvement in performance. Rare-earth reduced permanent magnets are considered a solution to these two problems. This thesis investigates the impact of chemical and morphological changes on the phase stability of rare-earth reduced hard permanent magnets. New methodologies for investigating the position preference of atomic substitutions and dopants have been applied to the RT12 (R = Rare-Earth, T = Transition metal) phase group. This work demonstrates that substitution of the transition metal for titanium in NdFe12, SmFe12, and SmCo12, decreases the cohesive energy, and therefore increases the stability of the structure up to 8Ti at.%. Through analysis of substitution positions it is demonstrated this is tied to a structural effect, derived from a switch in the symmetry of preferential substitution positions. To gauge the manufacturing feasibility of one of these phases, computational investigations of the melting temperature of NdFe12 at various pressures were performed using a Solid Liquid coexistence methodology applied in Molecular Dynamics. Pair potentials used for this work were generated by a genetic algorithm potential fitting methodology, which has application beyond the RT12 phase group. Finally, a new methodology for understanding grain morphology is presented, which takes into consideration the shape, surfaces, and interfaces of cyrstalline grain structures. This methodology is tested on the FePt L10 structure, which is able to produce stable magnetic grains at nanometer sizes, due to it’s magnetic anisotropy of Ha = 6-10 MJ/m . This work shows that at grain sizes between 3-9nm, the morphology of the grains is dominated by surface energy, and will result in structures with {111} planes as their primary faces. This result has implications for the design of next generation hard drives.
dc.description	Engineering and Physical Sciences Research Council (EPSRC)
dc.language	en
dc.publisher	University of Exeter
dc.publisher	College of Engineering, Mathematics, and Physical Sciences
dc.rights	http://www.rioxx.net/licenses/all-rights-reserved
dc.subject	Material Science
dc.subject	Crystals
dc.subject	Magnets
dc.subject	Magnetism
dc.subject	Morphology
dc.subject	Crystal Grains
dc.subject	Granular Structures
dc.subject	Nd2Fe14B
dc.subject	Nd2Fe12
dc.subject	Electric Cars
dc.subject	Nanoengineering
dc.subject	Molecular Dynamics
dc.subject	LAMMPS
dc.subject	GULP
dc.subject	RT12
dc.subject	SmCo12
dc.subject	SmFe12
dc.subject	New Magnetic Structures
dc.subject	Permanent Magnet Motors
dc.subject	Phase-Stability
dc.subject	Dopants
dc.subject	NdFe11Ti
dc.subject	NdFe12-xTix
dc.subject	Titanium Substitution
dc.subject	High Information Density Recording Media
dc.subject	Hard Disks
dc.subject	Superparamagnetic Limit
dc.subject	Nanometer Size Grains
dc.subject	Boltzmann Distribution
dc.subject	Boltzmann Factors
dc.subject	Cascading Probabilities
dc.subject	Probability Comparison
dc.subject	Manufacturing
dc.subject	NPT Ensemble
dc.subject	NVT Ensemble
dc.subject	Python Package
dc.subject	Material Science Toolkit
dc.subject	Polycrystals
dc.subject	Polycrystalline Structures
dc.subject	0912 Materials Engineering
dc.subject	030307 Theory and Design of Materials
dc.subject	High Performance Magnets
dc.subject	High Information Density Hard Drives
dc.subject	Hard Drives
dc.subject	Permanent Magnetic Recording
dc.subject	Permanent Magnets
dc.subject	Stabilising Crystals
dc.subject	Grain Boundaries
dc.subject	Surface Energy
dc.subject	Grain Shapes
dc.subject	Energy Driven Grain Models
dc.subject	Toolkit
dc.title	Impact of Chemical and Morphological Changes on the Phase Stability of Magnetic Materials
dc.type	Thesis or dissertation
dc.type	PhD in Engineering
dc.type	Doctoral
dc.type	Doctoral Thesis