Magnetotransport Study Of Low-Dimensional Structures Of Semiconductors And Magnetic Metals

It is of great importance to understand the electron spin related properties of materials. In this thesis, we investigated the electron spin related properties of the low dimensional structures of narrow band gap semiconductors, Hg Te and In Ga As, as well as Co/Pt magnetic multilayers, via magnetotransport experiments in low temperature and strong magnetic fields. We obtained the following results:(1) We investigated the spin susceptibility of the two-dimensional electron system confined in the Hg Te surface quantum well. By perfoming magnetotransport measurements in both perpendicular and tilted magnetic field, we analized the evolution of the longitudinal magnetoresistance with the tilt angle and extracted the spin susceptility according to the coincidence method. The results show that our samples have very large spin susceptibility ||**gmr, which ranges from 1.4 to 3.4. These results are much higher than the reported values of Hg Te/Hg1-xCdxTe quantum wells. In addition, the spin susceptibilty ||**gmr of our samples has no significant dependence on the filling factor, which is different from the result of Hg Te/Hg1-xCdx Te quatum wells. We attribute these differences to the unique band structure of our samples.(2) We investigated the zero-field spin splitting and high-field effective g-factor of the two dimensional electron system of an asymmetrical In0.53Ga0.47As/In0.52Al0.48 As quantum well. The longitudinal magnetoresistance xxR doesn’t show any sign of the beating effect of Shubnikov de-Haas oscillations, but indeed shows the weak anti-localization effect, which indicates our sample has finite zero-field spin splitting. In high magnetic field, we extracted the effective g-factor by analizing the double-peak structure of the longitudinal magnetoresistance due to the strong enough total spin splitting. The obtained result is *g =8.18 ~ 11.49, which is highly enhanced by the electron exchange interaction in high magnetic field and shows no dependence on the tilt angle. We analized the Dingle plot of the Shubnikov de-Haas oscillations of our sample and found that the Dingle plot shows a non-linear feature, which indicates the long range scattering potential from the doping Be atoms near the substrate has a great influence on the Sd H oscillation of our sample.(3) We investigated the perpendicular magnetic anisotropy of Co/Pt magnetic multilayers and its dependence on film thickness and temperature by measuring the anomalous Hall effect. The result shows that Sample A with a smaller Pt layer thickness has superparamagnetism instead of perpendicular magnetic anisotropy, while Sample B shows strong perpendicular magnetic anisotropy. Although the transverse Hall magnetoresistance xyR shows no sign of perpendicular magnetic anisotropy, the longitudinal magnetoresistance xxR shows a complicated behavior, which is similar to that of a spin valve from an overall view. The temperature dependences of the magnetic anisotropy of the two samples are also different: the characteristic magnetic field kB of Sample A has a simple exponential function like dependence on the temperature; however, Sample B’s coercive field cB has a dependence on the temperature T, which can be obviously divided into two zones at the criticle temperature 40 KcT ?. The value of s is different in the two zones: below cT, there is s = -0.013 and above cT s = -0.019. Our results indicate that the perpendicular magnetic anisotropy of Co/Pt magnetic multilayers is significantly affected by factors such as the Pt layer thichiness, electron scattering mechnisms including phonon scattering and magnon scattering and the two-dimensional ferromagnetism.