Electro-magnetic Transport Characteristics Of Individual Multilayered Nanometer Magnetic Structures

With the discovery of Giant Magneto-Resistance?GMR?and wide application of spin valve GMR in commercial memory and sensor,it has caused great enthusiasm for giant magnetoresistance study and gradually formed a new discipline of spintronics.Because the rapid development of semiconductor technology and the electronic devices market strongly demand for highly integrated,low energy consumption to promote the miniaturization of electronic devices and basic unit size has reached to nano-scale,so it is important to measure the functional device at the nanoscale in-situ and real-time.This thesis mainly concentrate upon the magnetic and transport properties of multilayer nanowire/thin film at the micro-nano scales.We have designed and manufactured the in-situ electron microscope magnetic transport device to measure the magnetoelectric transport properties of multilayer nanowires and thin films.The effects of interfacial transition layers on the magnetoelectric transport properties of multilayer structures were investigated in detail.The main contents of this thesis include the following aspects:?1?Designed and manufactured in-situ magnetic measurement instrument based on scanning electron microscopy?SEM?.It mainly includes: nano-manipulator,localized magnetic field,power control system,and other sub-system measurements.The test results show: nano-manipulator can achieve three-dimensional motion,the motion accuracy can reach 0.18 nm;localized magnetic field can achieve any angle of uniform magnetic field,the maximum magnetic field up to 1756 Oe;power control system can achieve a linear amplification of-350 V 350 V high voltage output range.It has an advantage of wide frequency response range,strong load capacity,etc.The movement of in-situ magnetic measurement instrument was tested,magnetoelectric transport properties of multilayer nanowires and thin films were measured using the instrument in the SEM.The results show that the instrument can provide a dynamic and graphical measurement for individual magnetic nano materials.?2?The Fe₃₀Co₆₁Cu₉/Cu multilayered nanowires were prepared by electrochemical deposition.The morphology,crystal structure and chemistry of Fe₃₀Co₆₁Cu₉/Cu multilayered nanowires were investigated at nanoscale.The results show that the diameter of the multilayer nanowires is about 50 nm and the length is about 50 m,and the FeCo layer and the Cu layer exhibit periodic distribution.The crystalline structure of individual Fe₃₀Co₆₁Cu₉/Cu MNWs was characterized in detail using high-resolution transmission electron microscopy?HRTEM?and selected area electron diffraction?SAED?techniques.The interfacial layers between the Fe₃₀Co₆₁Cu₉ and Cu layers were measured to be approximately 2.5 nm,ranging from 2 nm to 4 nm in thicknesswith a irregular and rough edge.The magnetization reversal mechanism of multilayered nanowires and FeCo alloy nanowires have been successfully investigated,which indicated the magnetization process was governed by the coherent rotation of the moments in this work described by cosine model and Stoner-Wolhfarth model,respectively.?3?The electrical properties of individual Fe₃₀Co₆₁Cu₉/Cu multilayered nanowires was accurately measured using nano-manipulators in in-situ scanning electron microscopy,which reveal that the interfacial transition layers have a great effect on their transport behaviors.The resistivity and the maximum fusing current of multilayer nanowires,alloy nanowires and Cu nanowires were obtained respectively.The multilayered nanowires have a maximum resistivity and a minimum fusing current.The resistivity of the copper layer of MNWs was then simulated according to the Mayadas-Shatzkes model.The calculation and analysis of the resistance of the interfacial transition layer in a Fe₃₀Co₆₁Cu₉/Cu MNW revealed that it would initially burn out when applied an external electrical field.The clarification of the role of interfacial layer in individual multilayer nanostructures is significant for understanding the electrical resistance and origins of giant magnetoresistance of a single multilayer nanowire and the design of novel functional multilayer structures for future industrial applications.The magnetization reversal mechanism of multilayer nanowires and FeCo alloy nanowires were also studied.The magnetoresistance of multilayer nanowires was obtained by in-situ measurements,MR is only 0.97%,by magnetic particles membrane resistance simulation calculation shows the result is 1.03%.Calculation and analysis of the MR of Fe₃₀Co₆₁Cu₉/Cu MNW proved that the instrument manufactured by ourself is reliable.?4?It is found that the interfacial transition layer has a great influence on the magneto-electrical properties of the multilayer structure.However,the interface layer of multilayer nanowire prepared by electrochemical deposition have an irregular shape which does not favor to study,In order to better understand the interface layer effecet on magnetoelectricity properties of multilayer structure,the multilayer magnetic thin films Fe₇₀Co₃₀/Cu/Fe₇₀Co₃₀/SiO₂,Fe₇₀Co₃₀/Cu/Fe₇₀Co₃₀/Cu/Fe₇₀Co₃₀/SiO₂ were prepared by RF-Magnetron sputtering method.To understand the transport mechanism of multilayer films,their morphology,chemistry,crystal structure,multilayer structure and interfaces were thoroughly characterized by HRTEM and other techniques.The results show that the multilayer films possessed magnetic layer /nonmagnetic layer/magnetic layer sandwich structure.The results of elements line scan shows the thickness of FeCo layer is about 5.6 nm,the thickness of Cu layer in the change,and interfacial transition layer thickness were also acquired.?5?Magnetic properties of multilayer films of the above two systems were studied at different temperatures.The coercivity of multilayer thin film system and the saturation magnetization change with temperature and thickness of Cu layer in multilayer thin films.The effect of Cu layer thickness on the magnetoelectric transport properties of multilayer films was also studied.It was found that the interfacial transition layer has significant effect on the magneto-electrical transport properties of multilayer thin films.The results showthat the interfacal transition layer has an important effect on the magnetic transport properties in the multilayer film system,which contribute to the increase of the interface scattering and grain boundary scattering.The thickness of the non-magnetic layer has a significant effect on the GMR effect in the multilayer thin films: when the thickness of the non-magnetic layer is small,the coupling enhancement between the adjacent magnetic layers which leads to an increase in the GMR effect.When the nonmagnetic layer thickness increases,the coupling between the layers reduced and eventually results in the decrease of GMR effect.An important factor affected the GMR effect is that the roughly crystal structure of the interface layer,which affects the scattering of the interface to the spin electrons.