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dc.contributor.authorFang, Zhou
dc.date.accessioned2017-11-06T10:07:03Z
dc.date.available2017-11-06T10:07:03Z
dc.date.issued2017-11-01
dc.identifier.urihttps://www.repository.cam.ac.uk/handle/1810/268099
dc.description.abstractThis thesis uses ferromagnetic resonance to explore the current-induced torques (CITs) in two different systems, namely YIG/heavy metal bilayers and bulk NiMnSb, at room temperature. We apply a microwave current to the sample while sweeping the external magnetic field, and measure the longitudinal DC voltage. From a symmetry analysis of the ferromagnetic resonance lineshape, the amplitudes and directions of the CITs parameterised by an effective magnetic field are accurately estimated. In Chapter 4, YIG samples of different thickness, capped by either Pt or Ta, are studied. The resonance is driven by both spin-transfer torque and Oersted field, and the DC voltage is attributed to both spin rectification and spin pumping. The CITs can be well analysed from the lineshape of the voltage and its dependence on YIG thickness, from which we deduce that the Oersted field dominates over the spin-transfer torque in driving magnetization dynamics. In Chapter 5, we characterise the CITs in bulk NiMnSb induced by the relativistic spin-orbit coupling effect. Both field-like and antidamping-like spin-orbit torques are observed and analysed in detail. At the end of this chapter, we study the spin-wave resonance driven by the CITs, from which the exchange stiffness of NiMnSb is determined. In Chapter 6, we extrapolate a new form of magnetoresistance in NiMnSb: unidirectional spin-orbit magnetoresistance (USOMR). USOMR scales linearly with the current and has opposite sign when the magnetization is reversed. Similar to the giant magnetoresistance in magnetic multilayers, USOMR can be used to distinguish between two opposite magnetization directions directly in the bulk of the ferromagnet.
dc.description.sponsorshipCambridge Trust scholarship
dc.language.isoen
dc.rightsNo Creative Commons licence (All rights reserved)
dc.rightsAll Rights Reserveden
dc.rights.urihttps://www.rioxx.net/licenses/all-rights-reserved/en
dc.subjectSpintronics
dc.subjectcurrent-induced torque
dc.subjectferromagnets
dc.subjectspin-orbit coupling
dc.subjectspin-orbit magnetoresistance
dc.subjectNiMnSb
dc.subjectYIG
dc.titleCurrent-induced torques in ferromagnets at room temperature
dc.typeThesis
dc.type.qualificationlevelDoctoral
dc.type.qualificationnameDoctor of Philosophy (PhD)
dc.publisher.institutionUniversity of Cambridge
dc.publisher.departmentDepartment of Physics
dc.date.updated2017-11-05T10:19:11Z
dc.rights.generalOnly for academic purposes
dc.identifier.doi10.17863/CAM.14322
dc.publisher.collegeJesus College
dc.type.qualificationtitlePh.D. in Physics
cam.supervisorCiccarelli, Chiara
cam.supervisorFerguson, Andrew
rioxxterms.freetoread.startdate2018-11-06


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