Spin conversion at interfaces

Most of the technological devices that we use in our daily life are based on electronics. Electronics is based on the movement of electrons through a (semi)conducting material. But as the electrons move in such materials, they will scatter around leading to a loss of energy that is converted into waste heat. One of the main breakthroughs of the last decades is the development of the transistor. A transistor is a device used to amplify or switch electronic signals. Since its development the scaling of electronic circuits has been leading to fast and steady improvement on their efficiency of operation. These advances led to the development of personal computers, mobile phones, touch screens, etc. In 1965 Gordon Moore predicted that the number of transistors in an integrated circuit (or chip) will double every two years. This is now known as Moore’s law. The predictions of Moore’s law worked for around 50 years but in the last decades it seems that the law is coming to a dead end. As the dimension of chips diminishes and the number of transistors grows, the control of the required electric currents to make them work becomes more difficult due to quantum effects and the above-mentioned waste heat. This brings the urgency of new approaches that do not rely on miniaturization of the devices to improve the efficiency of operation of a chip. Magnon spintronics is a promising solution to this issues. It relies on the interaction between electronic spins in a metal with spins in a magnetic material, in general through interfaces. In a magnetic insulator electrons do not move inside the material, avoiding the generation of waste heat. Nevertheless, it is possible to use both the wavelike perturbations of the magnetic order of the spins, known as magnons, as well as spin currents to encode and ultimately transport information. In this thesis we analyzed diverse aspects of magnon spintronics considering both ferromagnetic insulators and antiferromagnetic materials interfaced with metals. We studied the imprints of different phases of magnonic systems such as the quantum magnon Mott insulating state, as well as the hydrodynamic regime and the presence of viscosity in a magnon fluid. We also discussed how antiferromagnetic systems can be used to generate pure spin currents in response to mechanical deformations, and how to achieve Bose-Einstein condensation of excitons through an antiferromagnetic magnon-mediated interaction