Spin and Heat Transport Beyond Electrons: Ferromagnetic Insulators and Antiferromagnetic Metals

Magnon spintronics recently emerged as a fascinating topic. The scope of this Thesis is to investigate the spin and thermal transport in ferromag- netic insulators and antiferromagnetic metals with different theoretical approaches. In Chapter i, we introduce the magnon spintronics to readers who are new to the field. In Chapter 2, we develop a Green’s function formalism for spin transport through het- erostructures that contain metallic leads and insulating ferromagnets. We consider ballistic spin transport by exchange magnons in a metal-insulator-metal heterostructure with and without disorder. The developed Green’s function formalism is a natural starting point for numerical studies of magnon transport in heterostructures that contain normal metals and magnetic insulators. In Chapter 3, we apply the stochastic Landau-Lifshitz-Gilbert formalism with spin-transfer torques to develop a theory for magnon drag in antiferromagnetic metals. The results show that antiferromagnetic metals might be used as a tunable source of spin current near the spin-flop transition field. In Chapter 4, we study the alignment-dependent thermal transport mediated by magnons across a magnetic junc- tion consisting of two ferromagnetic insulators, which mimics the structure of the re- cently proposed magnon spin valve. We present the conclusions and outlook of our research in Chapter 5.