Spin excitations in ultrathin metallic films

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The project consists of two subprojects. (a) Spin excitations in ultrathin films with a spontaneous skyrmion lattice: At the interface of an ultrathin film grown on a nonmagnetic substrate the translational symmetry is broken. The absence of the translational symmetry in the presence of a large spin-orbit coupling leads to a non-zero antisymmetric exchange interaction, known as Dzyaloshinskii-Moriya (DM) interaction. This antisymmetric exchange interaction can stabilize a chiral spin texture with whirling structures, known as skyrmion. Skyrmions have attracted lots of attentions during the last few years because of their interesting physics and also their potential applications in spintronics. One of the promising applications of skyrmions is in the so called skyrmion racetrack memory where the idea is to use a skyrmion as a bit. A detailed knowledge on skyrmion dynamics is highly desirable for further development of such memory devices. The dynamics of spin in a magnetic solid is usually described in terms of elementary collective magnetic excitations (magnons). In other to understand the dynamics of skyrmions the experimental investigations on magnon-skyrmion interaction are of particular fundamental interest. The idea of this project is to excite magnons in a nano-skyrmionic lattice formed in an ultrathin Fe film grown on Ir(111) and investigate the dynamics of the system. (b) Design of atomic scale magnonic crystals: In the emerging field of magnonics, the central idea is to use the elementary collective magnetic excitations (magnons) for encoding or transmitting information. The first steptowards realization of this idea is to design a medium on which different magnon modes can be excited. The medium should also provide a way of tuning the magnon band structure as it is desired.Magnons cover a rather wide range of energy (frequency) spectrum, starting from a few tenth of gigahertz up to hundreds of terahertz. The magnons group velocity depends on their energy (the higher the energy, the faster the magnons). For using ultrafast (terahertz) magnons in magnonics the first step is to design a template on which different magnon modes can be excited and manipulated. Therefore a new approach of materials design for terahertz magnonics is highly demanded. Our idea is to suggest a way of designing atomic scale magnonic crystals for terahertz magnonics based on multilayer thin films. The central point of this project would be to design magnetic multilayers, composed of alternating atomic layers of ferromagnetic metals, in which different magnon modes can be efficiently excited. In the next step we aim to provide a way of tuning the magnon band structure via changing the materials combination and the number of atomic layers. The results shall have an impact on the design of materials useful for terahertz magnonics, terahertz electromagnetic sensors and terahertz microwave filters.