Magnetization reversal in nano-sized magnetic structures

随着磁性材料尺寸的减小，为了避免热效应，磁性材料的各向异性必须成比例地增大。这引起了人们对具有高磁晶各向异性的磁性材料的关注，这些磁性材料不能用传统技术产生的磁场脉冲来逆转。我建议研究具有大磁晶各向异性的单畴磁性材料的磁化反转，并开发制造这些结构的新方法。结合具有不同各向异性、交换刚度和磁化强度的磁层，研究单畴磁性材料的非均匀磁化反转，并对现有理论模型进行检验。在磁晶各向异性较大的磁性材料中，除了3d电子外，4d、5d、4f电子也对磁序有贡献。激光脉冲可以相干地反转来自4f电子的磁矩和来自d电子的热不稳定磁矩，因为它们相对于费米能级的位置。这将用于实现过渡金属-稀土磁性材料的飞秒磁反转。极化自旋电流通过纳米级磁性材料，产生与阻尼共线的自旋力矩。这种自旋力矩效应也将用于研究具有大磁各向异性的磁性材料中的弛豫和反转。为了控制非均匀磁化反转，磁性材料的所有三个维度都必须低于几十纳米。利用电子束光刻技术，利用外延生长多层结构制备纳米磁性材料和纳米柱状样品的周期阵列。

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.