We present studies of the electical detection of spin injection and transport in InSb/CoFe heterostructures. As a narrow gap semiconductor, InSb has a high mobility and strong spin-orbit interaction. Using ferromagnetic CoFe, lateral InSb/CoFe devices are fabricated by semiconductor processing techniques. The saturation magnetizations of various CoFe electrodes with different widths are calculated from Hall measurements in which the fringing fields of the CoFe electrodes are detected. A magnetic model provides reasonable estimation of the saturation magnetization for micrometer scale geometries. The interface magnetoresistance measurements of InSb/CoFe thin film layered structures present a unique peak at low field, having a symmetric behavior in magnetic field with a critical field Hc and a strong temperature dependence. We attribute our signal to a ferromagnetic phase in the InSb induced by spin injection. In a non-local lateral spin valve measurement, we observed the following. Firstly, Hc of the lateral spin valve signals is identical to Hc of interface magnetoresistance signals. Secondly, the non-local lateral spin valve signals are strongly dependent on temperature, which is also a unique characteristic magnetoresistance. Thirdly, the signals are tunable in response to an applied injector bias. Lastly, the signals are dependent on the exact interfaces. Based on these observations, the detected signals may be considered as spin current signals. The Hall and magnetoresistance signals are measured locally and non-locally in InSb/CoFe Hall devices. The non-local magnetoresistance signals exhibit asymmetric behavior in applied magnetic field which are considered as signatures of spin phenomena. The non-local Hall signals present switching behavior with the CoFe magnetization switching at the coercive field. The non-local Hall signals in a perpendicular field show Hc, similarly seen in non-local lateral spin valves. Inverse spin Hall effect measurements with tilted magnetic fields show an in-plane magnetic field dependence in non-local type Hall signal and a perpendicular magnetic field dependence in the local Hall measurement. We have found that the signal can have its origin in a spin current from our observation of Hc and hysteresis in the magnetization traces. As yet, the spin current transport mechanism is unknown. / Ph. D.

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Lee Kwok San = 二維海森堡模型的熱力學性質之數値硏究 / 李國姗. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 106-108). / Text in English; abstracts in English and Chinese. / Lee Kwok San = Er wei hai sen bao mo xing de re li xue xing zhi zhi shu zhi yan jiu / Li Guoshan. / Abstract --- p.i / Acknowledgement --- p.iii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- History of magnetism --- p.1 / Chapter 1.2 --- History of Heisenberg model --- p.2 / Chapter 1.3 --- Heisenberg model and high-Tc superconductors --- p.6 / Chapter 1.4 --- Organization of thesis --- p.8 / Chapter 2 --- Methodology --- p.10 / Chapter 2.1 --- Introduction --- p.10 / Chapter 2.2 --- Exact diagonalization --- p.11 / Chapter 2.2.1 --- Coding with only total Sz conservation --- p.11 / Chapter 2.2.2 --- Coding by using translational symmetry --- p.12 / Chapter 2.2.3 --- Coding with H acting on spin configuration --- p.17 / Chapter 2.2.4 --- Coding on finding eigenvalues and eigenvectors --- p.20 / Chapter 2.3 --- Coding on calculating dynamic properties --- p.20 / Chapter 2.3.1 --- Coding on calculating thermal properties --- p.20 / Chapter 2.3.2 --- Coding on calculating other thermal property --- p.21 / Chapter 3 --- Finite temperature calculations on unfrustrated spin systems --- p.30 / Chapter 3.1 --- Introduction --- p.30 / Chapter 3.2 --- Finite temperature calculations --- p.33 / Chapter 3.2.1 --- Energy spectrum E(k) --- p.33 / Chapter 3.2.2 --- Internal energy (E) --- p.39 / Chapter 3.2.3 --- Heat capacity Cv --- p.42 / Chapter 3.2.4 --- Uniform susceptibility x --- p.45 / Chapter 3.2.5 --- Staggered magnetization mz+ --- p.47 / Chapter 3.3 --- Linear Spin Wave Theory --- p.48 / Chapter 3.3.1 --- Linear Spin Wave Theory at zero temperature --- p.48 / Chapter 3.3.2 --- Linear Spin Wave Theory at finite temperature --- p.54 / Chapter 3.4 --- Phase Transition --- p.57 / Chapter 4 --- Finite temperature calculations on frustrated systems --- p.62 / Chapter 4.1 --- Introduction --- p.62 / Chapter 4.2 --- Finite temperature calculations --- p.65 / Chapter 4.2.1 --- Energy spectrum E(k) --- p.65 / Chapter 4.2.2 --- Internal energy (E) --- p.68 / Chapter 4.2.3 --- Heat capacity Cv --- p.69 / Chapter 4.2.4 --- Uniform susceptibility x --- p.71 / Chapter 4.2.5 --- "Fourier transform of susceptibility S(qx,qy)" --- p.72 / Chapter 4.3 --- Linear Spin Wave Theory --- p.73 / Chapter 5 --- Finite Size Scaling --- p.78 / Chapter 5.1 --- Introduction --- p.78 / Chapter 5.2 --- Infinite unfrustrated system --- p.79 / Chapter 5.2.1 --- Ground state energy E0 --- p.79 / Chapter 5.2.2 --- Internal Energy (E) --- p.80 / Chapter 5.2.3 --- Staggered magnetization mz+ --- p.81 / Chapter 5.3 --- Infinite frustrated system --- p.83 / Chapter 5.3.1 --- Ground state energy E0 --- p.84 / Chapter 6 --- Comparisons between unfrustrated system and frustrated system --- p.87 / Chapter 6.1 --- Energy spectrum E(k) --- p.88 / Chapter 6.2 --- Internal energy (E) --- p.91 / Chapter 6.3 --- Heat capacity Cv --- p.92 / Chapter 6.4 --- Uniform susceptibility x --- p.93 / Chapter 7 --- Spin Lattice Relaxation l/T1 --- p.94 / Chapter 7.1 --- Introduction --- p.94 / Chapter 7.2 --- Spin temperature --- p.95 / Chapter 7.3 --- Experimental setup and its principle --- p.97 / Chapter 7.4 --- Numerical calculations --- p.102 / Chapter 8 --- Conclusion --- p.104 / Bibliography --- p.106 / Chapter A --- Method of moments --- p.109

Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Physics. / M̲i̲c̲ṟo̲f̲i̲c̲ẖe̲ c̲o̲p̲y̲ a̲v̲a̲i̲ḻa̲ḇḻe̲ i̲ṉ A̲ṟc̲ẖi̲v̲e̲s̲ a̲ṉḏ S̲c̲i̲e̲ṉc̲e̲. / Includes bibliographical references. / Ph.D.

Zhao Kun. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese. / Zhao Kun.

Total energy calculations based on density functional theory are generally a good approach to obtain the properties of solids. The local density approximation (LDA) is widely used for calculating the ground state properties of electronic systems; for excited states the errors are in general unknown. The important aspects of LDA pertain to the modeling of the exchange-correlation interaction. If the exchange-correlation potential is approximately the same for the ground and excited states, one expects good results from the LDA calculations for excited states. In this thesis, we utilize the total energy technique for numerical computations of the electronic structure of iron in several magnetic phases and crystalline structures. 1. Body-centered-cubic iron in the ferromagnetic and several antiferromagnetic configurations. We use the total energy results to obtain the parameters in a model Heisenberg Hamiltonian. These include the interaction parameters up to 6-th nearest neighbors. Based on this model Hamiltonian we calculate properties such as the critical (Curie) temperature and spin stiffness constant. We assume that the total exchangecorrelation energy functional is the same in the ferromagnetic ground state and the antiferromagnetic excited states. Our model parameters are based directly on ab initio calculations of the electronic structure. Our calculation yields good results compared with experimental values and earlier work. Some other physical quantities, related to the phase transition, and spin waves are also discussed. 2. Face-centered-tetragonal iron. If iron is grown on a proper substrate ( e.g., Cu(100) ), the crystal structure of the thin film displays a face-centered-tetragonal distortion due to the lattice constant misfit between the film and substrate. Therefore, we performed calculations for fct iron in its ferromagnetic, antiferromagnetic, and nonmagnetic phases for a wide range of values of the lattice parameters. In the ferromagnetic calculations, we found two minima in the total energy: one is close to.the bcc structure and the other ( with a lower energy ) is close to fcc. In the antiferromagnetic and nonmagnetic calculations, we found in each case that there is only one minimum near the fcc structure, providing us clear evidence that the antiferromagnetic and nonmagnetic states are (meta)stable near the fcc region and unstable in bcc region. The antiferromagnetic and nonmagnetic states are almost degenerate near the fcc minimum, but the antiferromagnetic phase has the lowest total energy in the whole fct region. Magnetic moments are also calculated for a variety of fct structures. Near the fcc minimum we found that two ferromagnetic phases co-exist, one with a low spin and one with a high spin. These results are consistent with experimental facts and other earlier calculations. Some structural properties, such as the elastic constants and the bulk modulus, are also studied and compared with experimental data and some earlier calculations. / Graduation date: 1992

Thesis (Ph. D.)--School of Chemistry and Biochemistry, Georgia Institute of Technology, 2004. Directed by Z. John Zhang. / Vita. Includes bibliographical references.

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