While in conventional superconductors coupling between electrons and phonons is known to be responsible for the electron pairing, for the high temperature superconductors the pairing media remains under debates. Since the interactions of electrons with other degrees of freedom (phonons, magnetic excitations, etc) manifest themselves by an additional renormalization in the electronic dispersion, they can be investigated by means of Angle Resolved Photoelectron Spectroscopy. In the work renormalization in two families of high Tc cuprates have been studied. Along the diagonal of the two-dimensional BZ, the renormalization effects are represented by an unusual band dispersion that develops a so-called ‘‘kink’’. In the vicinity of the (pi, 0) point of the BZ, where the order parameter reaches its maximum, the renormalization is noticeably stronger and makes itself evident even in the shape of a single spectral line measured for a fixed momentum. It was shown that for the Bi-2212 samples substitution of Cu atoms in Cu-O plane changes renormalization features in ARPES spectra both in nodal and antinodal parts of the Brillouin zone. The smearing of the dip in the in the spectral line shape measured at (pi; 0) point can be well explained by coupling of electrons to the magnetic resonance mode. The effect of Zn and Ni substitution on the antinodal ARPES spectra was shown to be in good agreement with the influence of these impurities on magnetic resonance mode seen in inelastic neutron scattering experiments. This, in addition to the previous ARPES studies of temperature and doping dependence of peak-dip-hump structure, mass renormalization near antinodal region and a kink in the nodal part of Brillouin zone, provides further evidence that the coupling to magnetic excitations, rather than to phonons, is responsible for the observed unusual renormalization. Unlike the well studied Bi-2212 family of cuprates, photoemission on YBCO-123 turns out to be much more complicated. The observed spectra have a strong contribution from a heavily overdoped surface component with the hole doping level of about x~0.30, which is weakly dependent on the sample stochiometry. Absence of any signs of superconductivity in the spectra of the overdoped component was argued to result from the unusually high doping level. This conclusion is supported by the fact that the overdoped bands give rise to the Fermi surface and band structure consistent with the predictions of the LDA calculations, as well as, by the dependence of the photoemission matrix element on the excitation energy, which closely follows that of the superconducting bulk component. Specific experimental geometry was used to enhance the signal coming from the superconducting component. In particular, experiments with circularly polarized light bundled with simple theoretical considerations enabled better separation of the surface and the bulk components. This type of experiments also suggests that the overdoped component is mainly localized in the topmost CuO2 bilayer, while the next bilayers in the YBCO-123 structure already represent bulk properties and retain superconductivity. Using partially Ca substituted samples it was possible to obtain spectra with a suppressed overdoped component. The likely reason for the suppression is a shift of the most probable cleavage plane from the Ba–O interface to the Y layer. Spectra from the Ca substituted sample clearly reveal a sizable superconducting gap, and strong renormalization effects in the vicinity of the antinodal point. The fact that the renormalization vanishes above Tc and has strong momentum dependence, diminishing away from the (pi; 0)/(0; pi) point, strongly suggests that the reason for this renormalization in YBCO-123 is coupling of the electronic subsystem to spin resonance, similar to the case of Bi-2212.

Für die theoretische Beschreibung verschiedener Substanzen, so z.B. für diverse Kuprate die Anwendungen als Hochtemperatur-Supraleiter finden, spielt das t-J-Modell eine wichtige Rolle. In vielen Fällen kann man Abweichungen der Verbindungen vom idealen translationsinvarianten Festkörper vernachlässigen, für bestimmte Eigenschaften ist jedoch der Einfluß von Störstellen,z.B. Dotieratomen, bedeutsam. Um solche Verunreinigungen einzubeziehen, behandelt die vorliegende Arbeit das t-J-Modell mit einer zusätzlichen on-site-Energie mit über die Gitterpläte zufallsverteilten Werten. Um für dieses Modell die Einteilchen-Greensfunktion zu bestimmen, wird ein Verfahren entwickelt, welches auf der Projektionstechnik basiert und die Einbeziehung des Unordnungsterms ermöglicht. Die notwendige Mittelung über die möglichen Unordnungskonfigurationen erfolgt näherungsweise durch Faktorisierung und ist verwandt mit der sogenannten average T-matrix approximation, wird hier jedoch auf ein stark korreliertes System erweitert. Zur Illustration wird der Grundzustand von La2−xSrxCuO4 und Nd2−xCexCuO4 bei einem zusätzlichen Ladungsträger über Halbfüllung untersucht. Wie Bandstrukturrechnungen zeigen, ruft die Dotierung der elektronendotierten Substanz gerade einen solchen Zufallsterm hervor. Dies wurde in der bisherigen Literatur meist vernachlässigt. Bei der Übertragung der Bandstrukturergebnisse in die Modellparameter des t-t′-t′′-J-Modells zeigt sich, daß der Einfluß der Dotieratome bei La2−xSrxCuO4 um etwa eine Größenordnung geringer ist als in Nd2−xCexCuO4 . Als wichtige Ursache hierfür wird der Einfluß der Apex-Sauerstoffatome angesehen, die im Fall von La2−xSrxCuO4 die Seltenerd- Dotieratome gegenüber der Kupferoxidebene abschirmen. Für das mit diesen Parametern belegte Modell wird anschließend die Einteilchen- Greensfunktion berechnet, die Ausgangspunkt der Berechnung verschiedener Observablen ist. Die für die elektronendotierte Substanz auftretende lokale Mode gibt zu dem Vorschlag Anlaß, daß die unterschiedliche Stabilität der antiferromagnetischen Phase für die beiden betrachteten Substanzen nicht nur auf die Art der Ladungsträger zurückzuführen ist, sondern auch auf die Struktur der Elementarzelle. / The t-J-Modell can be applied to several classes of materials, e.g. high-Tc cuprate superconductors. Often translational invariance can be assumed, but sometimes it is necessary to take into account the effects of the doping atoms at randomly distributed sites. Therefore a t-J-Modell with an additional randomly distributed on-site energy is investigated. To calculate the one-particle Green’s function considering this term of disorder, a method is developed which bases on projection technique. The average over the possible configurations of the dopand atoms is approximated by factorization and is similar to the so-called average T-matrix approximation. Here it is extended to a model with strong correlations. In order to illustrate the methode the single-particle ground state of La2−xSrxCuO4 and Nd2−xCexCuO4 is analyzed. Band-structure calculations exhibit that for the electron-doped case the doping atoms (in first approximation) induce indeed a term of disordered on-site energies. The transformation of the values of this energies at the copper sites into the parameters in the t − t′ − t′′ − J-model shows that the influence of doping in La2−xSrxCuO4 is by about an order of magnitude smaller than in Nd2−xCexCuO4 . The existence of apex oxygen atoms between the rare-earth plane and the copper-oxygen plane in La2−xSrxCuO4 is one important reason for that effect. The single-particle Greens function for the t-t′-t′′-J-model with these parameters is calculated. A local mode appears in the electron-doped case, which suggests that the differences of the stability of the antiferromagnetic phases in both compounds are not only due to the type of charge carriers but also due to the structure of the unit cell.

No description available.

Questa tesi di dottorato studia l’interazione della cooperatività con il rumore in sistemi realistici, focalizzandosi principalmente sulla superradianza. Gli effetti cooperativi emergono dall’interazione collettiva di un insieme di elementi con un campo esterno. Esempi degni di nota sono la superconduttività, dove le coppie di Cooper elettroniche interagiscono con le vibrazioni reticolari, le eccitazioni di plasma, che sorgono dall'interazione collettiva degli elettroni in un metallo con il campo coulombiano, e la superradianza, ovvero quel processo di emissione spontanea cooperativa che sorge da un aggregato di emettitori identici. Gli effetti cooperativi sono tipicamente robusti al disordine e al rumore, cosa che li rende interessanti per delle applicazioni a dispositivi quantistici che possano operare a temperatura ambiente. In questo lavoro, inizialmente, introduciamo un formalismo di “master equations” che descrive l’accoppiamento collettivo di un aggregato di emettitori/assorbitori con il campo elettromagnetico, valido quando le dimensioni dell'aggregato sono sia maggiori che minori della lunghezza d’onda emessa/assorbita. Inoltre, il formalismo è valido per accoppiamento sia debole che forte con il campo elettromagnetico e, cosa più importante, permette di descrivere correttamente la superradianza in diversi regimi. In tale formalismo, studiamo l’interazione tra superradianza e rumore termico sia per nanotubi molecolari (di dimensioni minori della lunghezza d’onda associata alla transizione) che sono presenti nei complessi antenna fotosintetici dei Green Sulfur Bacteria, sia pure per superreticoli di quantum dots di nuova generazione, aventi dimensioni maggiori della lunghezza d’onda emessa. In entrambi i casi si dimostra che la coerenza può permanere in presenza di rumore termico alle temperature a cui questi sistemi sono stati analizzati sperimentalmente (temperatura ambiente per i nanotubi molecolari, e 6 K per i superreticoli di quantum dots). Nello specifico, nei nanotubi molecolari mostriamo che la macroscopica delocalizzazione coerente delle eccitazioni a temperatura ambiente, che copre centinaia di molecole, può essere considerata un effetto emergente che origina dall’effetto combinato della specifica disposizione geometrica delle molecole e della presenza di accoppiamenti tra subunità del cilindro, incrementati dagli effetti cooperativi. Questi risultati aprono la strada a nuovi modi per ingegnerizzare dei “quantum wires” robusti al rumore grazie alla cooperatività. Inoltre, la presente analisi di sistemi allo stato solido basati su superreticoli di “quantum dots” di perovskite (CsPbBr3) fornisce una base teorica in grado di comprendere recenti osservazioni di emissione superradiante. Sulla base della nostra teoria, suggeriamo che futuri esperimenti dove si utilizzino quantum dots più piccoli, potrebbe aumentare significativamente la robustezza del sistema al rumore termico, aprendo la strada verso la superradianza a temperatura ambiente in sistemi allo stato solido. Si considerano anche i complessi antenna dei Purple Bacteria, dove è ben risaputo che gli effetti cooperativi incrementano il trasferimento e l’accumulo di eccitazioni generate dalla luce assorbita. Mostriamo come queste proprietà possono essere sfruttate per creare un laser ispirato a sistemi biologici e basato su aggregati molecolari, dove la luce solare, benché debole, sarebbe utilizzata come sorgente di pompaggio. Il trasferimento efficiente di energia dentro questo sistema, all’atto pratico, focalizzerebbe l’eccitazione assorbita in direzione di un dimero molecolare, composto da una coppia di molecole interagenti, opportunamente scelte. L’orientazione dei momenti di dipolo di transizione in ciascun dimero è tale da concentrare tutta l’intensità del dipolo nel livello a più alta energia, lasciando lo stato eccitonico inferiore otticamente inattivo. Un dimero molecolare in tale configurazione, che è ideale per ottenere inversione di popolazione, è chiamato “H-dimer”. Tale H-dimer, nell’archittettura qui proposta per un laser ispirato a sistemi biologici, è posto al centro di un aggregato molecolare ispirato a sistemi biologici. Gli H-dimers, eccitati dagli aggregati molecolari circostanti, raggiungono inversione di popolazione e, dunque, possono emettere luce laser quando tali aggregati sono posti in una cavità ottica. Convertire l’energia incoerente fornita dal Sole in un fascio laser coerente supererebbe diverse limitazioni pratiche inerenti all’utilzzo della luce solare come sorgente di energia pulita. Per esempio, i fasci laser sono molto efficienti nell’avviare reazioni chimiche che convertono la luce solare in energia chimica. Inoltre, dal momento che i complessi fotosintetici batterici tendono ad operare nella regione spettrale del vicino infrarosso, la nostra proposta si presta in modo naturale a realizzare laser a infrarossi a corta lunghezza d’onda, i cui fasci viaggerebbero per lunghe distanze senza quasi perdere energia, quindi distribuendo in modo efficiente l’energia solare raccolta. Nella ricerca di un meccanismo comune alla cooperatività e alla sua robustezza, abbiamo confrontato il modello delle coppie di Cooper della superconduttività con la superradianza in singola eccitazione, mostrando molte somiglianze tra i due fenomeni: in particolare, i sistemi superradianti presentano una “gap” immaginaria nel piano complesso (ovvero, una segregazione tra i tempi di vita degli autostati del sistema) che, in modo simile alla gap superconduttiva, rende questi sistemi robusti al rumore statico. Più in generale, mostriamo che ogni interazione a lungo raggio tra i costituenti di un sistema induce effetti collettivi, manifestati da delle gap nello spettro eccitonico. Perciò, la nostra analisi successiva considera l’effetto delle interazioni a lungo raggio sul trasporto eccitonico lungo catene disordinate. Dimostriamo che la presenza di uno stato collettivo ben separato dagli altri stati influenza tutto lo spettro del sistema, generando dei regimi molto controintuitivi dove il trasporto è incrementato dal disordine o è indipendente da esso, e tali regimi si estendono su molti ordini di grandezza nell’intensità del disordine. Dimostriamo anche che una catena fortemente accoppiata a un modo del campo elettromagnetico in una cavità ottica è equivalente a una catena con interazione a lungo raggio, mostrandosi dunque molto promettente per esperimenti e applicazioni future. Nello specifico, mostriamo che catene molecolari realistiche, ioni intrappolati realizzati allo stato dell’arte e atomi di Rydberg sono tutti in grado di raggiungere l’intensità di interazione a lungo raggio tale per cui il trasporto sarebbe incrementato dal disordine o indipendente da esso, puntando alla realizzazione di un trasporto di energia senza dissipazione in “quantum wires” disordinati. / This Ph.D. thesis studies the interplay of cooperativity and noise in realistic systems, largely focusing on superradiance. Cooperative effects emerge from the collective interaction of an ensemble of elements to an external field. Notable examples are superconductivity, where the electron Cooper pairs interact with the lattice vibrations, plasmon excitations, arising from the collective interaction of electrons in a metal with the Coulomb field, and superradiance, that is a cooperative spontaneous emission process stemming from an aggregate of identical emitters. Cooperative effects are typically robust to disorder and noise, making them interesting for applications to quantum devices operating at room temperature. In this work, we first present a general master equation formalism that describes the collective coupling of an aggregate of emitters/absorbers to the electromagnetic field, valid both when the size of the aggregate is larger or smaller than the emitted/absorbed wavelength. Also, the formalism is valid both for weak and strong coupling of the emitters to the electromagnetic field and, most importantly, it allows to correctly describe superradiance in different regimes. Within such formalism, the interplay of superradiance and thermal noise is studied both for molecular nanotubes (of size smaller than the transition wavelength) that are present in the antenna complexes of photosynthetic Green Sulfur Bacteria, and also for novel solid state quantum dot superlattices, having size larger than the emitted wavelength. In both cases it is shown that coherence can persist in presence of thermal noise at the temperatures where these systems have been experimentally analyzed (room temperature for molecular nanotubes, and 6 K for quantum dot superlattices). Specifically, in natural molecular nanotubes we show that the macroscopic coherent delocalization of the excitation at room temperature, covering hundreds of molecules, can be considered an emergent effect originating from the combined effect of the specific geometric disposition of the molecules and the presence of cooperatively enhanced couplings between cylinder subunits. These results open the path to new ways of engineering quantum wires robust to noise thanks to cooperativity. Moreover, our analysis of solid state systems based on perovskite (CsPbBr3) quantum dot superlattices provides a theoretical framework able to explain recent observations of superradiant emission. Based on our theory, we suggest that further experiments, using smaller quantum dots, could significantly increase the robustness of the system to thermal noise, paving the way towards room-temperature superradiance in solid-state systems. We also considered the antenna complexes of Purple Bacteria, where cooperative effects are well known to boost the transfer and storage of photo-absorbed excitations. We show how these properties can be exploited to create a bio-inspired molecular aggregate laser medium, where natural sunlight, although weak, would be used as a pumping source. The efficient energy transfer within this system would effectively focus the absorbed excitation on a suitably chosen molecular dimer, composed by a pair of interacting molecules. The orientation of the molecule transition dipole moment in each dimer is such to concentrate all the dipole strength in the highest energy level, leaving the lower excitonic state dark. A molecular dimer in such configuration, which is ideal to achieve population inversion, is called H-dimer. Such an H-dimer in our proposed architecture for a bio-inspired laser medium, is placed at the center of the bio-inspired molecular aggregates. The H-dimers, pumped by the surrounding molecular aggregates, reach population inversion and, therefore, can lase when such aggregates are placed in an optical cavity. Turning the incoherent energy supply provided by the Sun into a coherent laser beam would overcome several of the practical limitations inherent in using sunlight as a source of clean energy. For example, laser beams are highly effective at driving chemical reactions which convert sunlight into chemical energy. Further, since bacterial photosynthetic complexes tend to operate in the near-infrared spectral region, our proposal naturally lends itself for realising short-wavelength infrared lasers which would allow their beams to travel nearly losslessly over large distances, thus efficiently distributing the collected sunlight energy. In search of a common mechanism to cooperativity and its robustness, we have compared the Cooper pair model of superconductivity and single-excitation superradiance, showing many similarities between the two: in particular, superradiant systems present an imaginary gap in the complex plane (that is, a segregation between the lifetimes of the system eigenstates) that, similarly to the superconducting gap, makes these systems robust to static disorder. More in general, we show that any long-range interaction between the constituents of a system generates collective behaviours, manifested by gaps in the excitonic spectrum. Therefore, our further analysis considers the effect of long-range interactions on excitation transport along disordered chains. We show that the presence of a gapped, collective state affects the whole spectrum of the system, generating quite counter-intuitive disorder-enhanced and disorder-independent transport regimes, that extend over many orders of magnitude of the disorder strength. We also prove that a chain strongly coupled to a cavity mode is equivalent to a long-range interacting chain, thus being very promising for future experiments and applications. Specifically, we show that realistic molecular chains, state-of-the-art trapped ions and Rydberg atoms are all able to reach the needed long-range interaction strength that would show disorder-enhanced or disorder-independent transport, aiming to the realization of dissipationless transport of energy in disordered quantum wires.

<p>In recent years, correlated magnetic phenomena have emerged as a unique resource for enabling alternative computing, memory, and sensing applications. This has led to the exploration of novel magnetic hybrid platforms with the promise of improved figures of merit over the state-of-the-art. In this dissertation, we delve into several example platforms where magnets interact with various other degrees of freedom, resulting in enhanced figures of merit and/or the emergence of novel functionalities.</p><p>First, we investigate the possibility of utilizing the collective resonant mode of nanomagnets to enhance the electric field sensitivity of quantum spin defects. While quantum systems have garnered significant attention in recent years for their extraordinary potential in information processing, their potential in the field of quantum sensing remains yet to be fully explored. Quantum systems, with their inherent fragility to external signals, can be harnessed as powerful tools to develop highly efficient sensors. In this dissertation, we explore the potential of a specific type of quantum sensor, namely the quantum spin defects as an electric field sensor, when integrated with a nanomagnet/piezoelectric composite multiferroic. This integration yields at least an order of magnitude enhancement in sensitivity, presenting a promising avenue for quantum sensing applications.</p><p>Next, we shift our focus towards harnessing magnetic correlation in the emerging class of atomically thin magnets known as van der Waals magnets. These magnets provide distinctive opportunities for controlling and exploiting magnetic correlations. Specifically, these platforms allow for tunable magnetic interactions by twisting two vertically adjacent layers of the magnet, features that are unique to van der Waals materials. By capitalizing on such twist degrees of freedom, we demonstrate the creation of twist-tunable nanoscale magnetic ground states. This capability opens up avenues for applications such as high-density memories and magnon crystals.</p><p>Interestingly, the same material platform also allows for exploiting magnetic correlation by controlling the local electrical environment. We uncover the symmetry-allowed spin-charge coupling mechanisms in the heterostructures of such magnets, a prediction that has received experimental support. Utilizing such an understanding, we propose a setup for the electrical generation of magnons. Magnons—the elementary excitation of spin waves—have garnered a lot of attention these days due to their potential to couple various diverse physical systems and in the field of low dissipation computing. Our findings offer a potential pathway towards the realization of magnon-based spintronic devices.</p>

This master’s thesis focuses on investigating the electronic properties of the superconducting spinel compound LiTi2O4 by means of computational and experimental effort. The title compound has been extensively studied in the past years, being the only known superconducting spinel oxide with relatively high Tc = 11.5 K. Even so, the origin of its superconducting mechanism is under debate, and its anomalous superconductivity is still inquired. Thanks to the recently developed ability to produce high-quality epitaxial LiTi2O4 thin films, a renewed research interest in this compound has matured. With this work, we partake in this challenge and present combined experimental and computational results on the electronic band structure of the material. Density functional theory (DFT) has been employed for the first principle electronic structure calculations performed with the Quantum ESPRESSO software. Furthermore, thin-film samples were in-situ realized with the pulsed laser deposition (PLD) method and investigated through the angle-resolved photoemission spectroscopy (ARPES) technique conducted at the ULTRA end-station of the SLS synchrotron facility at PSI in Switzerland. Here, we report the computed electronic band structure of LiTi2O4, with a detailed investigation of its density of states and Fermi surface. Further, we compare these calculations with the obtained experimental ARPES data. Emerging from this study are results supporting the non-conventional superconducting nature of LiTi2O4, which presents coexisting correlation effects, such as electron-phonon coupling and enhanced electron-electron interactions. / Denna masteruppsats fokuserar på att undersöka de elektroniska egenskaperna hos det supraledande spinellmaterialet LiTi2O4 med hjälp av datorsimuleringar samt experimentella mätningar. LiTi2O4 har studerats omfattande under de senaste åren, eftersom den är den enda kända supraledande spinelloxiden med relativt hög Tc = 11.5 K. Trots det är ursprunget till dess supraledande mekanism debatterad, och meaknismen för dess okonventionella supraledning är fortfarande inte helt förstådd. Tack vare den nyligen utvecklade förmågan att producera tunna högkvalitativa epitaxiella LiTi2O4 filmer, har ett förnyat forskningsintresse för denna förening mognat. Med detta arbete deltar vi i denna utmaning och presenterar kombinerade experimentella och beräkningsresultat om materialets elektroniska bandstruktur. Densitetsfunktionsteori (DFT) har använts för principiella elektroniska strukturberäkningar utförda med Quantum ESPRESSO-mjukvaran. Vidare realiserades tunnfilmsprover in-situ med pulsed laser deposition (PLD) medoden och undersöktes experimentellt via vinkelupplöst fotoemissionsspektroskopi (ARPES) som utfördes vid ULTRA-ändstationen på SLS synkrotronanläggningen vid PSI i Schweiz. Här rapporterar vi den beräknade elektroniska bandstrukturen för LiTi2O4, med en detaljerad undersökning av dess tillståndstäthet och Fermi-yta. Vidare jämför vi dessa teoretiska beräkningar med de erhållna experimentella ARPES data. Resultat från denna studie stöder den icke-konventionella supraledande naturen hos LiTi2O4, som också uppvisare samexisterande korrelationseffekter, såsom elektron-fononkoppling samt starka elektron-elektron-interaktioner.

No description available.

No description available.

<p>    </p> <p>We live in an age in which computation touches upon every aspect of our lives in ever increasing ways. To meet the demand for increased computing power and ability, new computation strategies are continually being proposed. In this dissertation, we consider two research projects related to two such cutting edge paradigms. We first consider developing superconducting devices that implement asynchronous reversible ballistic computation. This paradigm was developed to circumvent Landauer’s principle of a minimum energy required per bitwise computation operation. We report the design of a new device, the rotary, which is a critical step towards developing universal computation gates in the scheme of synchronous reversible ballistic computation. Next, we turn to the consideration of anyons which have been predicted to enable topological quantum computing, a quantum computing paradigm that is relatively immune to environmental noise. We consider initial steps in the development of a Bethe ansatz solvable model that will help decipher the many-body properties of Majorana zero modes in superconducting Kitaev wires. </p>

<p>  </p> <p>Magnetism plays a vital role in the technologies of today, and materials used for magnetic applications largely consist of solid state phases. Intermetallic chalcogenides are one such material which have exhibited a full range of properties useful for a variety of applications requiring soft magnets, superconductors, magnetocalorics, and even rarer magnetic phenomenon such as 1D Heisenburg magnetic chains. Solid state chemists continue to develop new synthesis methods for chalcogenides as they produce both new phases and modifications of existing phases, usually with the express intent of improving their physical and chemical properties. Low dimensional chalcogenides often have predictable structure-property relationships which when understood aids in these efforts of optimizing existing materials.</p> <p>In this work, we have synthesized novel, low-dimensional Tl1-xAxFe3Te3 (A = K, Na)-based magnetocalorics for magnetic refrigeration technologies utilizing a variety of synthetic methods. Doping of alkali metals into the thallium site simultaneously reduces the toxicity and cost of the material, and also modifies their crystal structures leading to changes in their magnetic properties including ordering temperature, magnetic anisotropy, magnetic hysteresis, coercivity, and magnetic entropies. Most notably, the magnetic ordering temperature has been boosted from 220 K of the prior known TlFe3Te3 phase up to 233 K in the new Tl0.68Na0.32Fe2.76Te3.32 phase, further towards room temperature which is required for the commercialization of magnetic refrigerants for home appliances. There exist strong magnetostructural correlations for most of the alterations in the magnetic properties, and relationships have been modelled where trends exist to match the magnetism to the changes in the unit cell of the structure.</p> <p>New synthetic methods were also developed for the ternary TBi4S7 (T = transition metal) phase which exhibits a pseudo-1D structure of Heisenberg antiferromagnetic chains. These synthetic techniques resulted in more consistent high purity of phases than methods reported previously in literature. Attempts at synthesizing new phases were made, and crystallographic and composition analysis methods suggested the synthesis of a new Mn1-xCoxBi4S7 phase, though magnetic impurities prevented characterization of this new material’s magnetic properties. </p>