| Summary: | 碩士 === 國立中正大學 === 物理所 === 95 === Fe3O4 has been suggested an ideal electrode due to its high spin polarization and high Curie temperature (~856K). However, for most studies of magnetic tunneling junction(MTJ) with Fe3O4 as electrode shows relatively low MR ratio. The present study modifies the MTJ structure, using Fe3O4 as an interlayer(3nm) next to MgO insulating layer and obtain high MR ratio up to ~ 50%.
We use Molecular Beam Epitaxy (MBE) system to produce high-quality magnetic tunneling junction Fe(30nm)/Fe3O4(3nm)/MgO(2nm)/Fe(30nm)/MgO(001) film. The MTJ films were first characterized using of XRD and VSM to explore the structural and magnetic properties. The multilayer was then patterned into ellipse-shaped cell-array with cell size of 1200 to 7850 μm2. Magnetoresistance(MR) measurement is carried out by using standard four-probe stage. During the MR measurement, a magnetic field is applied parallel to the film in the range of -600 to 600 Oe.
The result of X-ray diffraction shows that Fe film has (002) texture. Magnetic hysteresis shows double loop characteristic and in-plane 2-fold symmetry. The MR measurement shows a strong in-plane anisotropy effect with RA of 20 kΩ-μm2 along magnetic easy axis and the highest MR ratio is up to 50% although most cells show MR ratio ~5%. However, in the MR loop the switching behavior is not abrupt but extends over a range of ~200 Oe, it is due to bias voltage field that is caused by interfacial effect of Neel Coupling.
In addition, the I-V curve of the device presents the non-linear effect, which is consistent with Simmon's theory. In this thesis, we also discuss the influence of half-metal (Fe3O4) in MTJ and the way to promote the MR value in these devices.
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