The spin-glass is a peculiar magnetic phase, exhibiting non-trivial dynamics at low temperatures, characterized by an continuously evolving state without long-range order. The behavior requires some degree of disorder to occur, often in the way of impurities or random exchange energy between the spins. However, recent research have found structurally ordered systems exhibiting glassy behaviour. This project aims to further investigate these self-induced spin-glasses. The report provides a short introduction to atomistic spin-dynamics and applies the theory to study self-induced spin-glasses in hexagonal systems with the help of simulations. A variation approach was applied by running simulation using a range of spin-exchange couplings in the Heisenberg Hamiltonian. These systems were then studied by the means of their autocorrelation function and compared to known glassy systems from the Edwards-Andersson model. The resulting behaviour is presented for three different hexagonal structures and glassy behaviour is indicated in stacked hexagonal systems. It is however argued that the autocorrelation function is not sufficient to classify these systems, instead further observables are needed. Nevertheless, the method of studying self-induced spin-glasses by varying couplings in the Heisenberg Hamiltonian is promising. As even with the few spin interactions used in this report we observe the slow relaxation time associated with spin-glasses. Given some extra considerations when choosing the exchange used for the simulation, a self-induced glassy state should be able to be recreated using the method described in this report. / Spinn-glas är en speciell magnetisk fas som uppvisar icke trivial dynamik vid låga temperaturer, en kontinuerlig utveckling samt en avsaknad av ordning på stora skalor. Detta beteende kräver en viss gradav oordning för att uppstå, ofta i form av föroreningar i materialet eller slumpmässiga interaktioner mellan olika spinn. Forskning har dock visat att även strukturellt ordnade system kan uppvisa spinn-glas beteende. Därmed är målet med detta projekt att fortsätta undersöka dessa själv-inducerade spinn-glas. Rapporten ger en kort introduktion till atomistisk spinn-dynamik och applicerar denna teori för att studera själv-inducerade spin-glas i hexagonala system. I projektet simulerades system med varierande spin-interaktioner i Heisenberg Hamiltonianen. Dynamiken undersöktes med hjälp av en korrelationsfunktion som jämfördes mot kända spinn-glas från Edwards-Andersson modellen. Resultat presenteras för tre hexagonala strukturer och spinn-glas-liknande beteende observeras i de tre-dimensionella systemen. Det kan dock argumenteras att korrelationsfunktionen inte är tillräcklig för att klassificera dessa system och att mer kvantitativa mått krävs. Trots detta anses metoden, att variera spinn-interaktioner i Heisenberg Hamiltonianen, vara lovande. Detta eftersom den långa avslappningstiden associerad med spinn-glas påträffades, trots de få interaktioner som användes i denna rapport. Ett själv-inducerat spin-glass borde därmed kunna skapas med de metoder som presenteras i rapporten, givet en mer systematisk metod vid val av interaktionsparametrar för simuleringen.

Disordered multicomponent nitride thin film can be used for various applications. The focus of this Licentiate Thesis lies on the theoretical study of piezoelectric properties, phase stability and surface diffusion in multifunctional hard coating nitrides using density functional theory (DFT). Piezoelectric thin films show great promise for microelectromechanical systems (MEMS), such as surface acoustic wave resonators or energy harvesters. One of the main benefits of nitride based piezoelectric devices is the much higher thermal stability compared to the commonly used lead zirconate titanate (PZT) based materials. This makes the nitride based material more suitable for application in, e.g., jet engines. The discovery that alloying AlN with ScN can increase the piezoelectric response more than 500% due to a phase competition between the wurtzite phase in AlN and the hexagonal phase in ScN, provides a fundamental basis for constructing highly responsive piezoelectric thin films. This approach was utilized on the neighboring nitride binaries, where ScN or YN was alloyed with AlN, GaN, or InN. It established the general role of volume matching the binaries to easily achieve a structural instability in order to obtain a maximum increase of the piezoelectric response. For Sc0.5Ga0.5N this increase is more than 900%, compared to GaN. Y1-xInxN is, however, the most promising alloy with the highest resulting piezoelectric response seconded only by Sc0.5Al0.5N. Phase stability and lattice parameters (stress-strain states) of the Y1-xAlxN alloy have been calculated in combination with experimental synthesis. Hard protective coatings based on nitride thin films have been used in industrial applications for a long time. Two of the most successful coatings are TiN and the metastable Ti1-xAlxN. Although these two materials have been extensively investigated both experimentally and theoretically, at the atomic level little is known about Ti1-xAlxN diffusion properties. This is in large part due to problems with configurational disorder in the alloy, because Ti and Al atoms are placed randomly at cation positions in the lattice, considerably increasing the complexity of the problem. To deal with this issues, we have used special quasi-random structure (SQS) models, as well as studying dilute concentrations of Al. One of the most important mechanisms related to the growth of Ti1-xAlxN is surface diffusion. Because Ti1-xAlxN is a metastable material it has to be grown as a thin film with methods such as physical vapor deposition (PVD), in which surface diffusion plays a pivotal role in determining the microstructure evolution of the film. In this work, the surface energetics and mobility of Ti and Al adatoms on a disordered Ti0.5Al0.5N(001) surface are studied. Also the effects on the adatom energetics of Ti, Al, and N by the substitution of one Ti with an Al surface atom in TiN(001), TiN(011), and TiN(111) surfaces is studied. This provides an indepth atomistic understanding of how the energetics behind surface diffusion changes as TiN transitions into Ti0.5Al0.5N. The investigations revealed many interesting results. i) That Ti adatom mobilities are dramatically reduced on the TiN and Ti0.5Al0.5N(001) surfaces while Al adatoms are largely unaffected. ii) The reverse effect is found on the TiN(111) surface, Al adatom migration is reduced while Ti adatom migration is unaffected. iii) The magnetic spin polarization of Ti adatoms is shown to have an important effect on binding energies and diffusion path, e.g., the adsorption energy at bulk sites is increased by 0.14 eV.