Ferromagnetic Metal Spintronics In Dilute Magnetic Semiconductors And Semiconductor Quantum Dots Spectroscopy Study

The observation of microwave photovoltage in ferromagnetic materials isencouraging not only in that people finally find a way to generate electric power usingelectron spin but also in its enlightment on the physics about the inter-relationshipbetween magnetostatics and spin dynamics.First,we report electric detection offerromagnetic resonance (FMR) in epitaxially grown single crystal iron film throughmicrowave photovoltage (PV) technique.The experimental results agree well with theestablished theory about FMR in iron films,showing excellent extendability of such atechnique onto different ferromagnets as an effective way to study magnetocrystallineanisotropy and spin excitations.Furthermore,the information about the phase ofmagnetization precession is implicated in the lineshape of photovoltage,which makes itpossible to probe in details into magnetic phase dynamics that is of significance fordevising spintronic devices.Second,ferromagnetic resonance in Ga_0.98Mn_0.02As has beenelectrically detected through microwave PV technique as well.To extend the spinrectification theory to this promising material,general formalism of photovoltage undermagnetocrystalline anisotropy and arbitrary magnetization direction has been derived.The model turns out to agree with the data quite well,and the results are discussed in thespirit of a kinetic exchange picture,which reflects the Zener model nature of the carrier-mediated ferromagnetism in GaMnAs systems.Moreover,the observed unusualhysteresis of PV is understood in certain nucleation processes describable by the Stoner-Wohlfarth model.The sharp contrast provided by the hysteresis free magneto-transportmeasurement results uncovers the important role of microwave phase for PV generation.Based on this work,it is expected that the detection of microwave PV is not only apowerful way to study spin excitations but can also be applied to probe in detail intocomplicate magnetostatic processes.On the other hand,semiconductor in microscopic structures on a nanometer scale,like semiconductor quantum dots for instance,provides people with an excellent systemfor realizing accurate spin operation.By taking advantage ofμ-photoluminescence (μ-PL)spectroscopy,we first report the evolution of exciton states' emission in single InAs/GaAsquantum dots,a representative ofⅢ-Ⅴsystems,as a function of external magnetic field,which enables us to obtain the excitonic Land(?) g factor and its dependence on the excitonenergy.Then we switch toⅡ-Ⅵsystems,represented by CdSe/ZnSe quantum dots.For the Mn doped sample with the Giant Zeeman Effect introduced by s-d exchangeinteraction,we devise a tri-layer structure which proves to effectively enhance thequantum efficiency of luminescence,and implies a different mechanism accounting forthe suppression of radiative recombination with the presence of Mn impurities.For the undoped samples,we study the inter-dot coupling effect in a series of single quantum dot molecules through the splitting of ground exciton state's emission.The experimental data are well explained in iso-spin language by making an analogy of Bell entangled states.Asthe inter-dot separation distance decreases,the coupling strength increases gradually andbrings forth the red-shift of the emission peaks.Moreover,by investigating the finestructures of PL spectrum of single CdSe/ZnSe quantum dots,we probe into the spinrelated interactions on a quite small energy scale,such as the Coulomb interaction incharged exctions,the electron-hole exchange interaction and the exciton spin-nucleusspin hyper-fine interaction.