Optimized nanomagnetic system for spintronic applications
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Optimized nanomagnetic system for spintronic applications Mishel Morales Meza1, Paul P. Horley1 and Alexander Sukhov2, 1 CIMAV Chihuahua / Monterrey, 120 Av. Miguel de Cervantes, Chihuahua, CHIH 31109, México 2 Institut für Physik, Martin-Luther Universität Halle-Wittenberg Halle (Saale), 06099, Germany ABSTRACT Magnetic properties at nano-scale provide a whole spectrum of new phenomena that can be beneficial for spintronic devices characterized with ultra-short response time, high sensitivity to magnetic field and miniature size. The properties and stability of a magnetic system can be enhanced by creating ordered arrays of ferromagnetic nano-particles. Here we report a considerable reduction of coercitivity for a magnetic array using triangular, square and hexagonal particle arrangement. The reduction of coercitivity can be explained by fine-tuning of dipole-dipole interaction between magnetic particles, which is to large degree influenced by the number of nearest neighbors and distance between the particles. INTRODUCTION The discovery of the giant magnetoresistance [1, 2] paved a way for significant developments in nano-scale magnetic devices, leading to unprecedented increase in the density of information storage [3]. Yet, the small device size makes it susceptible to the destabilizing action of the temperature, which may degrade the required magnetic configuration. One of solutions providing more robustness to a spintronic device can be found in synchronization of several such devices – which may represent, for example, spin valves [4]. A spin valve is a multi-layer device formed with thick ferromagnetic polarizer layer and thin analyzer layer, separated with a non-magnetic spacer. Polarized layer is used to define spin orientation for the carriers passing through it, so that the dynamics of the analyzer layer can be effectively controlled with an applied magnetic field and a torque generated by spin-polarized current. Therefore, we considered ferromagnetic particles shaped as cylinders with diameter of 12 nm and height of 2.2 nm to mimic the geometry of analyzer layers of spin valves. These particle dimensions agree by the order of magnitude with particle size constrains when the magnetization rotation occurs in a uniform manner [5], permitting to use macrospin approximation [6]. With the current advances of nano-scale etching and lithography, we consider that it would be feasible to create the arrays of ferromagnetic nano-particles of the desired size and configuration. We considered several types of grids formed by regular polygons covering the surface – triangles, hexagons and squares. The working hypothesis was that the different number of neighbors – as well as distance between them – will be one of the factors defining the magnetic response of the system. As triangular grid has six nearest neighbors (while hexagonal and square ones have three and four nearest neighbors, respectively) it was expected that the particles arranged into triangular grid will be characterized with larger magnetic stiffness.
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