Effect of Oxygen Contents on Structural and Magnetic Properties of NiFe/Ni-oxide Bilayers
| Autor: | Zhong-Yi Guo, 郭仲儀 |
|---|---|
| Rok vydání: | 2005 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 93 The exchange coupling between ferromagnetic (FM) and antiferromagnetic (AF) thin films has received increasing attention because it plays an important role in magnetoresistance (MR) heads or spin valves. In this study, the structural and magnetic properties of Ni80Fe20/Ni-oxide bilayers prepared by an ion-beam deposition technique have been investigated. XRD results have shown that Ni-oxide composite films (7% O2) in the assisted beam consisted of a mixture of f.c.c Ni (a=3.52 Å) and rock-salt NiO (a= 4.21 Å) phases. The expanded lattice constant (4.32 Å) of the pure NiO phase has been observed for films prepared with 33% O2 in the assisted beam. TEM micrographs revealed that the grain sizes of these Ni-oxide films range from 5 nm to 10 nm. A strong temperature dependence of exchange field Hex was observed in the Ni80Fe20 (20 nm)/Ni-oxide (36 nm) bilayers whose magnitude increases with decreasing temperature. At T=150 K, the exchange field of this sample has been determined to be Hex~ -43 Oe. At room temperature, this Ni80Fe20/Ni-oxide bilayers exhibit good magnetic properties (Hc= 16 Oe，Hex= -45 Oe， |Hex/Hc|= 2.8 ), when applied a magnetic field (Happ.~ 300 Oe) during deposition. Magnetotransport properties have shown that the pure Ni film exhibits a resistivity of 28μm-cm, and it increases with increasing oxygen contents in the assist beam. Both Ni-oxide composite films and Ni80Fe20/Ni-oxide bilayers exhibit anisotropic magnetoresistance (AMR) behavior. At T= 298K and 77K, the total MR ratio for Ni80Fe20/Ni-oxide bilayers increases with increasing oxygen contents. The Ni80Fe20/NiO (33% O2) bilayers exhibit a maximum total MR ratio of 4.5% (T=77 K). |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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