Magnetization reversal in nano-sized magnetic structures

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As the size of magnetic material becomes smaller, its magnetic anisotropy has to be proportionally increased to avoid thermal effects. This puts attention to magnetic materials with high magnetocrystalline anisotropy that cannot be reversed with magnetic field pulses produced with conventional technologies. I propose to study magnetization reversal in single domain magnetic materials with large magnetocrystalline anisotropy and to develop new methods for fabrication of these structures. By combining magnetic layers with different anisotropies, exchange stiffness and magnetization, I will study nonuniform magnetization reversal in single domain magnetic materials and test existing theoretical models. In magnetic materials with large magnetocrystalline anisotropy, not only 3d electrons, but also 4d, 5d, or 4f electrons contribute to the magnetic order. Laser pulses can coherently reverse magnetic moments that originate from 4f electrons and thermally destabilize magnetic moments that originate from d electrons due to their position with respect to the Fermi level. This will be used to achieve femtosecond magnetic reversal in transition metal-rare earth magnetic materials. A polarized spin current passing through a nanometer size magnetic material induces a spin torque that is collinear with the damping. This spin torque effect will also be used to study relaxation and reversal in magnetic materials with large magnetic anisotropy. In order to control nonuniform magnetization reversal, all three dimensions of the magnetic material have to be below several tens of nanometers. Periodic arrays of nanometer-size magnetic materials and nanopillar shaped samples will be fabricated by e-beam lithography from epitaxially grown multilayer structures.