Magnetization reversal in nano-sized magnetic structures

随着磁性材料的尺寸变小，其磁各向异性必须成比例地增加，以避免热效应。这引起了人们对具有高磁晶各向异性的磁性材料的关注，这些材料无法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。通过组合具有不同各向异性、交换刚度和磁化强度的磁层，我将研究单畴磁性材料中的非均匀磁化反转，并验证现有的理论模型。在具有大磁晶各向异性的磁性材料中，不仅3d电子，而且4d、5d或4f电子对磁序有贡献。激光脉冲可以相干地逆转源自4f电子的磁矩，并且由于d电子相对于费米能级的位置而使源自d电子的磁矩热不稳定。这将被用来实现过渡金属-稀土磁性材料的飞秒磁反转。极化的自旋电流通过纳米尺寸的磁性材料时，会产生与阻尼值共线的自旋力矩。这种自旋扭矩效应也将被用来研究具有大磁各向异性的磁性材料的驰豫和反转。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在几十纳米以下。纳米磁性材料和纳米管状样品的周期性阵列将通过电子束光刻从外延生长的多层结构中制备出来。

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.