In this thesis we present three different aspects of spin and spin-dependent transport properties in novel materials. Spurred by the prospect of spintronic devices, which use the spin degree of freedom of electrons instead of, or combined with, the charge degree of freedom, we analyse the spin properties of quantum wires, organic conducting polymers and sheets of graphene. First, we examine a quantum wire that is embedded in a two dimensional electron gas. We consider the Rashba spin-orbit coupling, and include the effect of interaction between the conduction electrons. We construct an analytically solvable low-energy theory for the wire, and explore the interaction between two magnetic impurities in the wire. We find that both the spin-orbit coupling and the electron-electron interaction have an effect on the magnetic interaction, and find the magnetic interaction to be tunable by an electric field. Next, we study an organic conducting polymer, which is contacted to magnetised ferromagnetic leads. In semiconducting organic polymers the current is transported by spinful polarons and spinless bipolarons. We simulate the transport through the system, including both types of charge carriers, and find the current to be insensitive to the presence of bipolarons. In addition, we find the bipolaron density to depend on the relative magnetisation of the ferromagnetic contacts. This constitutes an optical way of measuring the spin accumulation in conducting polymers. Finally, we investigate the optical conductivity of graphene. Symmetry arguments indicate the existence of two kinds of spin-orbit coupling in the two dimensional lattice, but there is no consensus about the actual strength of these couplings. We calculated the microwave optical conductivity of graphene including both possible spin-orbit interactions. We find the low frequency dependence of the optical conductivity to have a unique imprint of the spin-orbit couplings. This opens a possibility to experimentally determine both couplings separately.

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<p dir="ltr">Molecular materials exhibiting bistability between two states are intriguing candidates for next generation electronic devices. Two similar classes of materials, known as spin crossover (SCO) and valence tautomers (VT) respectively, are of particular interest due to their multifunctional properties, which are controllable via several external parameters, such as temperature, light irradiation, pressure, magnetic field, and electric field. In recent years, considerable research has been dedicated to better understanding the underlying principles that govern the behavior of these materials, so that their implementation into nano-based devices might be achieved.</p><p dir="ltr">In this report, a systematic study of the valence tautomer molecule [Co(sq)(cat)(3-tpp)₂] is presented. In the first chapter, the phenomenon of valence tautomerism (VT) occurring in coordination compounds is introduced and described from the perspective of Crystal Field Theory (CFT). Further, the molecular structure and physical properties of the [Co(sq)(cat)(3-tpp)₂] molecule are explored. The properties of the ferroelectric material Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and the 2-D Mxene Ti₃C₂ are also discussed.</p><p dir="ltr">The next section details equipment development and experimental methods. Thin films of VT molecules were prepared from solution via a drop-casting approach. For thin film analysis, we have developed a custom made, fully automated Vibrating Sample Magnetometer (VSM) with a sensitivity on the order of 1 × 10^-5 emu, as well as a fully automated, variable temperature, under vacuum electron transport stage, and a magneto-optic Kerr effect apparatus (MOKE). Additional experimental methods used to characterize the VT thin films include X-ray Absorption Spectroscopy (XAS), UV-visible Spectrometry (UV-Vis) and Differential Scanning Calorimetry. Experimental results obtained from these techniques are discussed and analyzed in the third section. PVDF-HFP polarization dependent isothermal spin state switching of [Co(sq)(cat)(3-tpp)₂] is also discussed as well as the effects of doping [Co(sq)(cat)(3-tpp)₂] with Ti₃C₂, followed by a conclusion and an outline of future work.</p>

<p dir="ltr">The market for infrared detectors has grown significantly in recent years due to the wide variety of applications from astronomy to medical thermography. Additionally, several emerging applications for high-speed infrared technologies are in development such as infrared LIDAR, autonomous vehicles, semiconductor device analysis, and free space communication. Improvements in the readout-speed and sensitivity of uncooled infrared detectors are required for some of these applications, and have been a long-standing goal in the field. Two technologies currently dominate the detection of infrared radiation, photodiodes and bolometers. Bolometers are extremely interesting as they are currently the most sensitive infrared detectors (either cooled or uncooled). We will propose and demonstrate a new type of bolometric infrared detector based on a highly structured spintronic material. The device's detection mechanism utilizes thermally activated magnetic transitions in a nanoscale magnetic device. We will also discuss a classification for detectors based on their digital-mode (discrete) or analog (continuous) readout signals. We develop a stochastic model to compare the sensitivity of these detectors. From this model we demonstrate several fundamental limits in the measurement of temperature by infrared detection.</p>