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The effect of pressure on a number of magnetically interesting compounds such as single-molecule magnets and dimeric copper and manganese molecules has been investigated to probe the validity of ambient magneto-structural correlations. The first chapter is an introduction to the equipment and methodologies that have been adopted to carry out the experimental high-pressure work. The second chapter reports the first combined high-pressure single crystal X-ray diffraction and high pressure magnetism study of four single-molecule magnets (SMMs). At 1.5 GPa the structures [Mn6O2(Et-sao)6(O2CPh(Me)2)2(EtOH)6] (1) – an SMM with a record effective anisotropy barrier of ~86 K – and [Mn6O2(Etsao) 6(O2C-naphth)2(EtOH)4(H2O)2] (2) both undergo significant structural distortions of their metallic skeletons which has a direct effect upon the observed magnetic response. Up to 1.5 GPa pressure the effect is to flatten the Mn-N-O-Mn torsion angles weakening the magnetic exchange between the metal centres. In both compounds one pairwise interaction switches from ferro- to antiferromagnetic, with the Jahn-Teller (JT) axes compressing (on average) and re-aligning differently with respect to the plane of the three metal centres. High pressure dc χMT plots display a gradual decrease in the low temperature peak value and slope, simulations showing a decrease in |J| with increasing pressure with a second antiferromagnetic J value required to simulate the data. The “ground states” change from S = 12 to S = 11 for 1 and to S = 10 for 2. Magnetisation data for both 1 and 2 suggest a small decrease in |D|, while out-of-phase (χM //) ac data show a large decrease in the effective energy barrier for magnetisation reversal. The third SMM is the complex [Mn3(Hcht)2(bpy)4](ClO4)3·Et2O·2MeCN (3·Et2O·2MeCN) that at 0.16 GPa loses all associated solvent in the crystal lattice, becoming 3. At higher pressures structural distortions occur changing the distances between the metal centres and the bridging oxygen atoms making |J| between the manganese ions weaker. No significant variations are observed in the JT axis of the only MnIII present in the structure. Highpressure dc χMT plots display a gradual decrease in the low temperature peak value and slope. Simulations show a decrease in J with increasing pressure although the ground state is preserved. Magnetisation data do not show any change in |D|. The fourth SMM, [(tacn)6Fe8O2(OH)12](ClO4)3.9Br4.1⋅6H2O, (4) is the largest inorganic compound ever studied at high-pressure. Up to 2.0 GPa the conformation of the complex remains largely unaffected, with the counter ions and water molecules moving around to accommodate a compression of the unit cell volume. High pressure magnetic susceptibility data collected up to 0.93 GPa confirm minimal changes in the intra-molecular exchange interactions. The third chapter focuses on three hydroxo-bridged CuII dimers: [Cu2(OH)2(H2O)2(tmen)2](ClO4)2 (5), [Cu2(OH)2(tben)2](ClO4)2 (6) and [Cu2(OH)2(bpy)2](BF4)2 (7) have been structurally determined up to 2.5, 0.9 and 4.7 GPa, respectively. 6 and 7 have never been reported before. Pressure imposes important distortions in the structures of all three complexes, particularly on the bond distances and angles between the metal centres and the bridging hydroxo groups. 5 undergoes a phase transition between 1.2 and 2.5 GPa caused by the loss of a coordinated water molecule. This leads to a loss of symmetry and dramatic changes in the molecular structure of the complex. The structural changes are manifested in different magnetic behaviours of the complexes as seen in dc susceptibility measurements up to ~0.9 GPa: J becomes less antiferromagnetic in 5 and 6 and more ferromagnetic in 7. The fourth chapter shows the compression of two oxo-bridged MnII/MnIII mixed valence dimers: [Mn2O2(bpy)4](ClO4)3⋅3CH3CN, (8) has been squeezed up to 2.0 GPa whilst [Mn2O2(bpy)4](PF6)3⋅2CH3CN⋅1H2O, (9) could be measured crystallographically up to 4.55 GPa. 9 has never been reported before, while 8 has been reported in a different crystallographic space group. The application of pressure imposes significant alterations in the structures of both complexes. In particular, in 8 the Mn-Mn separation is reduced by the contraction of some of the Mn-O bond distances, 9 shows essentially analogous behaviour: the Mn-Mn distance and nearly all the Mn-N bonds shrink significantly. The magnetic behaviour of the complexes has been measured up to 0.87 GPa for 8 and 0.84 GPa for 9, but neither display any significant differences with respect to their ambient data.

abstract: Recently, nanostructured metamaterials have attracted lots of attentions due to its tunable artificial properties. In particular, nanowire/nanohole based metamaterials which are known of the capability of large area fabrication were intensively studied. Most of the studies are only based on the electrical responses of the metamaterials; however, magnetic response, is usually neglected since magnetic material does not exist naturally within the visible or infrared range. For the past few years, artificial magnetic response from nanostructure based metamaterials has been proposed. This reveals the possibility of exciting resonance modes based on magnetic responses in nanowire/nanohole metamaterials which can potentially provide additional enhancement on radiative transport. On the other hand, beyond classical far-field radiative heat transfer, near-field radiation which is known of exceeding the Planck’s blackbody limit has also become a hot topic in the field. This PhD dissertation aims to obtain a deep fundamental understanding of nanowire/nanohole based metamaterials in both far-field and near-field in terms of both electrical and magnetic responses. The underlying mechanisms that can be excited by nanowire/nanohole metamaterials such as electrical surface plasmon polariton, magnetic hyperbolic mode, magnetic polariton, etc., will be theoretically studied in both far-field and near-field. Furthermore, other than conventional effective medium theory which only considers the electrical response of metamaterials, the artificial magnetic response of metamaterials will also be studied through parameter retrieval of far-field optical and radiative properties for studying near-field radiative transport. Moreover, a custom-made AFM tip based metrology will be employed to experimentally study near-field radiative transfer between a plate and a sphere separated by nanometer vacuum gaps in vacuum. This transformative research will break new ground in nanoscale radiative heat transfer for various applications in energy systems, thermal management, and thermal imaging and sensing. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2017

This research thesis reports experimental work done to design a stable magneticmicroemulsion of ionic liquid in 2-ethylhexyl laurate with the help of an ionic surfactant andan alcohol co-surfactant. The ionic liquids tested were based on a 1,3-dialkylimidazoliumcation with different alkyl chain lengths and a tetrachloroferrate anion ([FeCl4]+) to ensure theemulsion is sensitive to applied magnetic fields. Tests of solubility of these ionic liquids havebeen performed in different solvents and oils. Emulsification tests have been done withdifferent dispersing medium, surfactants as well as with different components quantities tofind the best composition possible. Polarity and chain length of alkyl radicals in ionic liquidsand hydrocarbons in alcohol co-surfactants were proved to affect the emulsification process.Shorter chains, and higher polarity of [C1C2im]+ [FeCl4]- (at 1wt%) combined with [C1C12im]+[FeCl4]- surfactant (between 3 and 5wt%) and non-polar 1-Hexanol co-surfactant (at 10 wt%)were the best combination to create a stable magnetic microemulsion in 2-ethylhexyl laurate. Applications for this microemulsion could vary from improved oil recovery to transport ofmaterials in liquid medium for examples and have all in common a better and tunablecontrollability of the used liquid via magnetic fields. / Denna forskningsuppsats rapporterar experimentellt arbete som gjorts för att designa enstabil magnetisk mikroemulsion av jonisk vätska i 2-EtylHexyllaurat med hjälp av ett jonisktytaktivt ämne och ett alkoholsamverkande ytaktivt ämne. De joniska vätskorna som testadesvar baserade på en 1,3-dialkylimidazoliumkatjon med olika alkylkedjelängder och entetraklorferratanjon ([FeCl4]+) för att säkerställa att emulsionen är känslig för applicerademagnetfält. Tester av lösligheten av dessa joniska vätskor har utförts i olika lösningsmedel ocholjor. Emulgeringstester har gjorts med olika dispergeringsmedium, ytaktiva ämnen samt medolika mängd komponenter för att hitta bästa möjliga sammansättning. Polaritet ochkedjelängd för alkylradikaler i joniska vätskor och kolväten i alkoholsamverkande ytaktivaämnen visade sig påverka emulgeringsprocessen. Kortare kedjor och högre polaritet för[C1C2im]+[FeCl4]- (vid 1 wt%) kombinerat med [C1C12im]+[FeCl4]- ytaktivt ämne (mellan 3 och 5 wt%) och opolär 1-hexanol medytaktivt medel (vid 10 wt% var den bästa kombinationen föratt skapa en stabil magnetisk mikroemulsion i 2-EtylHexyllaurat. Tillämpningar för denna mikroemulsion kan variera från förbättrad oljeutvinning tilltransport av material i flytande medium till exempel och har alla gemensamt en bättre ochavstämbar styrbarhet av den använda vätskan via magnetfält.