| Summary: | 碩士 === 國立交通大學 === 電子物理系所 === 99 === The main purpose of this research is to investigate the magnetic properties of patterned sub-micrometric Ni planar wires, including the magnetic anisotropies and microstructure inside. The geometry of the wire plays an important role in these magnetic behaviors. Therefore, in this work, individual Ni wires with different geometries (width w=0.2~10.0μm, length L=20~60μm, and thickness t=25 or 30nm) were systematically investigated to explore their magnetic properties.
We have measured the in-plane magnetoresistance of a series of sub-micrometric nickel planar wires at T＝10K to study the magnetic anisotropy, and scanned the magnetic force microscopic images to find out the microstructure of the wires. Strikingly, demonstrated by anisotropy magnetoresistance effect, our results indicate that samples have the strong transverse magnetic anisotropy despite the enhancement of longitudinal shape anisotropy.
The wires of large width (w＞2μm) have typical multi-domain structure. The magnetization reversal is via the well-known domain expansion and all behaviors are under expectation. Furthermore, the narrow wire with w＜1μm, according to their behaviors near the remnant state, are cataloged into two regions. For larger width with w＞0.6μm, the magnetoresistance（MR）curves exist coherent rotation background at large field, but the curve scanned from positive to negative magnetic field and the opposite ones cross near the remnant states, forming four packets for the irreversible part; for wire width with w＜0.6μm, however, existing the butterfly shoulder-shaped near the remnant states.
To find out the influences of shape anisotropy in the narrow wires with w＜1.0 μm, the configurations near remnant state and the form of the coherent rotation, namely, the reversible part of the MR curves, are analyzed in details. Also, a series of magnetic force microscope images of Ni planar wires（L＝21μm, w=0.2~4.9μm）were taken at the remnant state at room temperature. Our results demonstrate that the easy axis tends to lie along the short axis of wire. The strong shape anisotropy is not able to turn the easy axis to the long axis of the wire. Moreover, the transverse direction of the easy axis can be resulted from magnetoelastic anisotropy due to the lattice mismatch between Ni and SiN substrate.
|
|---|
