Magnetic Properties of Self-Aligned Fe, Mn Nanoparticles and Fe Capped Mn Nanoparticles on Nanostructured Template Al2O3/NiAl(100)
Date Issued
2007
Date
2007
Author(s)
Yen, Hong-Yu
DOI
en-US
Abstract
Interest in magnetic nanoparticles has increased in the recent years due to the industrial applications such as the ultra-high density storage device and the fundamental
interest in finite size effect. By naturally grown stripe structures with ~ 4 nm interdistance on the Al2O3 layer, Fe and Mn nanoparticles were prepared by self assembling. The surface morphology and magnetic properties were characterized by STM and MOKE, respectively. The 9~33 ML Fe and 0.1~16.9 ML Mn nanoparticles both reveal that the separation of particles decreases with increasing coverage. [1 ML is defined as the surface atom density: 1.54 × 10^15 at./cm2 on Cu(100).] The Fe nanoparticles are magnetic isotropic until 23 ML, and the twostep hysteresis loops of 23, 33 ML are ascribed to the uniaxial anisotropies with
the higher order term along the stripe directions, which is supported by the Stoner-Wohlfarth simulation. Mn nanoparticles are proven to be non-ferromagnetic at 0.1~8.5 ML and there is no exchange bias with Fe capped on 3.4~16.9 ML Mn at our lowest accessible temperature ~ 130 K. For 17.6 ML Fe capped n ML Mn (n= 3.4~16.9), the drastic reduction of magnetic moments and the enhancement
of coercivity were found at RT (room temperature), while at LT (150 K), the coercivity decreases unusually. The increasing roughness with increasing coverage of Mn and Fe-Mn interdiffusion account for the RT observations, and the temperature dependent reversed domain nucleation and domain wall pinning may be responsible for the LT behaviors.
Subjects
鐵奈米顆粒
錳奈米顆粒
磁性
鐵磁覆蓋層
臺階狀磁滯曲線
Fe nanoparticle
Mn nanoparticle
magnetism
Fe capping layer
two-step hysteresis loop
Type
thesis