The Umklapp Scattering and Spin Mixing Conductance in Collinear Antiferromagnets

Abstract

Antiferromagnetic spintronics is a new promising field in applied magnetism. Antiferromagnetic materials display a staggered arrangement of magnetic moments so that they exhibit no overall magnetization while possessing a local magnetic order. Unlike ferromagnets that possess a homogeneous magnetic order, the spin-dependent phenomena occur locally upon the interaction between the itinerant electron and the localized magnetic moments. In fact, unique spin transport properties such as anisotropic magnetoresistance, anomalous Hall effect, magnetooptical Kerr effect, spin transfer torque and spin pumping have been predicted and observed, proving that antiferromagnetic materials stand out as promising candidates for spin information control and manipulation, and could potentially replace ferromagnets as the active part of spintronic devices. As a matter of fact, owing to their vanishing net magnetization, they produce no parasite stray fields, hence, they are mostly insensitive to external magnetic fields perturbations and displaying ultrafast magnetic dynamics.

When a spin current is sent into an antiferromagnet, it experiences spin-dependent scattering, a mechanism that controls the spin transfer torque as well as the spin transmission across the antiferromagnet. The fully compensated antiferromagnetic interfaces are full of intriguing properties. For example, itinerant electron impinging on such an interface experiences a spin-flip associated with the sub-lattices interchange. This process, associated with Umklapp scattering, gives rise to a non-vanishing spin mixing conductance that governs spin transfer torque, spin pumping, and spin transmission.

The thesis explores the mechanism of Umklapp scattering at a staggered antiferromagnetic interface and its associated spin mixing conductance. In this project we consider two systems of bilayer and trilayer antiferromagnetic (L-type, G-type) heterostructures. We first study the scattering coeffcients at the interface implemented by adopting the tight-binding model and proper boundary conditions. Then, in the trilayer case, we study the spin mixing conductance and the dephasing length associated with the transition from ferromagnetic order to antiferromagnetic order.