The ever-increasing demands for higher computing capabilities and low energy consumption has necessitated the developing of micro or nano electronics and sensors. This results in increasing demand for faster, higher performance, more compact and low energy consumption devices and sensors which pushes microelectronics to its physical limit. Driven by size, cost, sensitivity, reliability and power consumption, the electronic and magnetic related devices are entering a completely new age where innovations on new materials and physics are being explored. Among the most promising materials, magnetoelectric multiferroic (MEMF) and topological insulators (TI) have attracted a great deal of interest, since they are promising for their unique properties and innovative applications. The coupling of electric and magnetic properties of MEMF and the ultrahigh surface carrier mobility of TI enlighten the design of devices with extremely low thermal losses and energy cost.

However, most of the device implementations of these material systems are still in status of ideas and laboratory prototypes. The prospects of practical realization of devices based on MEMF and TI encounter several critical challenges: the low ME coupling coefficient and current leakage in magnetoelectric(ME) sensor; fabrication large scale, low roughness and large terrace width of TI thin films for industry utilization; the high bulk conductivity and low sensitivity of TI based magnetic sensors. The present thesis will address some problems and challenges based on the above questions.

In this work, several aspects regarding to achieve a high performance and low energy consuming devices were investigated including: systemically studied and manipulated the energy band structure of TI for nanosized electronics and sensors application; developed Hall effect sensor and anomalous Hall effect sensor based on magnetically doped topological insulator; explored a method to increase the ME coupling coefficient of ME sensors; There are nine chapters in this dissertation. Chapter 1 gives general background to readers on magnetic sensors which used widely in daily life. Basic physics of two kinds of important materials: topological insulators and MEMF composites will also be introduced. Besides that, chapter 1 will also introduce a proposed switching device which integrates both two kinds of materials. The last part of chapter 1 will be the motivation and objectives of work in this dissertation. Chapter 2 will review the experiments, techniques and equipment used for research in this dissertation including sample fabrication methods and testing methods. Starting from chapter 3, topological insulators material fabrication and sensor application will be introduced based on different kind of TIs. Study on MEMF sensors will be introduced in chapter 8. Chapter 9 is a summary of all the work and gives some general conclusions of this dissertation.