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Current-induced torque driven ferromagnetic resonance in magnetic microstructures 10.17863/CAM.16583 Fang, Dong This Dissertation explores the interaction between the magnetisation and an alternating current in a uniform ferromagnetic system. Diluted magnetic semiconductors (Ga,Mn)As and (Ga,Mn)(As,P) have been studied. Due to their strong spin-orbit coupling and well-understood band-structure, these materials are well-suited to this investigation. The combined effect of spinorbit coupling and exchange interaction permits the alternating current to induce an oscillating current-induced torque (CIT) on the magnetisation. In the frequency range close to the natural resonance frequency of the magnetic moments (gigahertz), CIT can excite precessional motion of the magnetisation, a process known as ferromagnetic resonance (FMR). CIT can be parameterised by an effective magnetic field. By analysing the lineshape of the measured FMR signals, the magnitude and orientation of this effective field have been accurately determined. Moreover, the current-induced fields in these ferromagnetic materials have been observed with symmetries of the Dresselhaus, and for the first time, Rashba spin-orbit coupling. A new class of device-scale FMR technique, named as CIT-FMR, has been established in this Dissertation, with the advantage of simple device structure (only a resistor is required) and scalability (measurements has been performed on devices sized from 4 μm down to 80 nm). This technique is not only limited to magnetic semiconductors, but can also be transferred to study other ferromagnetic systems such as ultrathin metal films. Finally, the CIT-FMR technique is employed to study the magnetic anisotropy in individual (Ga,Mn)As and (Ga,Mn)(As,P) micro-devices. Devices down to 80 nm in width have been measured in (Ga,Mn)(As,P), which show strong strain-relaxation-induced anisotropy, larger than any previously reported cases on (Ga,Mn)As. Furthermore, due to the tensile-strain on the (Ga,Mn)(As,P) epilayers, the anisotropy field due to patterning-induced strain-relaxation in these devices is observed to take the opposite direction compared to that in the compressively-strained (Ga,Mn)As samples. University of Cambridge 2011-03-15 Thesis Doctoral Doctor of Philosophy (PhD) eng The research has been funded by the following organisations: Cambridge Overseas Trusts, Hitachi Cambridge Laboratory, Downing College, EU Grant FP7-214499 NAMASTE. http://www.dspace.cam.ac.uk/handle/1810/241302 https://www.repository.cam.ac.uk/handle/1810/241302 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/77689e94-18b8-4201-a453-1641a615908a/download 0b1a12d4eb169023d6d65183e2d7aac9 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/2c586e80-ac32-440c-ad5a-b8dc42161510/download 0779dac5d2ab135890f7259c911c26d0 https://www.rioxx.net/licenses/all-rights-reserved/ Ferromagnetic resonance SO-FMR Spintronics Ferromagnetic semiconductor GaMnAs Current-induced torque