Magnetization reversal in patterned NiFe/Cu/NiFe tri-layers by magneto-transport

• Main Authors: Ko, Sheng, 柯昇
• Other Authors: Hsu, Shih-Ying
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/27877940303134760371

碩士 === 國立交通大學 === 電子物理系所 === 102 === The main purpose of this workis to investigate the magnetic properties of patternedNiFe/Cu/NiFetri-layersby using magneto-transport measurements. For patterned ferromagnetic planar wiresof high aspect ratio, magnetic momentsare dominated by shape induced anisotropy andmagnetization reversal follows the curling mechanism.Thus,based on the properties, the tri-layers in planar wire configuration are expected to have a rapid switching between two resistance states in magneto-transport. Samples are made of two NiFe layers of different thicknesses. One is fixed to be 35nm thick. The other layer for three series is 20, 25, and 30nm in thickness, respectively. The spacer layer Cuis 8nm thick such that RKKY effect can be neglected. Samples were fabricated by lithographytechnique and thermal evaporation with sample length being kept at 20um and its width varying from 0.2 to 2.0um. We can investigate the influence of sample geometry on magnetic properties. All ofour tri-layer samples demonstrateGMR (Giant Magneto-Resistance) effect and the resistancevariationratiois about 3% ~ 4% at 10K.The abrupt switching due to curling is clearly present atroom temperature with about 1% ~2%in the resistancevariation ratio. In addition, when the magnetic field deviates the wire axis, the AMR effect appears. Such theresistancevariationratio in transverse magneto-resistance (TMR) is about 2% ~3%at 10K and about 0.5% ~1% at room temperature, respectively. The switching fields can be observedin the magneto-resistance curve with two NiFe layers of different thicknesses. The smaller switching field (Hsw1)of the thick layer increases with increasing the angle between the magnetic field and the wire axis, in coincidence with the result of a single wire of about the same thickness. It can be well described by the curling model. Theswitching field of the thin layeris larger than the expectationof the curling model. We suggest that exchange coupling between both layers tends to keep both moments in anti-parallelorientation and hence,the switching field is enhanced. Meanwhile, the switching field is insensitive to the sample thickness. TMR curves indicate thatall moments of both NiFe layers in tri-layers are in parallel and coherently rotate with magnetic field. Anisotropic energy Ku is obtained by fitting TMR curves of all samples. Ku and saturation fields are roughly proportional to sample thickness and the inverse of samplewidth as expected for a single NiFe wire. However, the value of Ku is smaller in tri-layers than a single NiFe wire of the same thickness. We suggest that whenboth moments of two layers are in parallel and coherentlyrotate with magnetic field, Ku is slightly affected by the exchange coupling.