22 - Spintronics of nanostructured manganese germanium (MnGe) dilute magnetic semiconductor

Abstract

With the apparent limit of scaling on CMOS microelectronics fast approaching, spintronics has received enormous attention as it promises next-generation nanometric magnetoelectronic devices; particularly, the electric field control of the ferromagnetic transition in dilute magnetic semiconductor (DMS) systems offers magnetoelectronic devices a potential for low power consumption and low variability. Special attention has been given to technologically important group IV semiconductor based magnetic materials, with a prominent position for MnGe. Since the first claim of the realization of a MnGe DMS, tremendous efforts have been concentrated on enhancing the Curie temperature and on interpreting the observed ferromagnetism in terms of DMS theories. In this chapter, we will first review the current theoretical understanding on ferromagnetism in MnGe DMS, pointing out the possible physics models underlying the complicated ferromagnetic behavior of MnGe. Then we carry out detailed analysis of MnGe thin films grown by molecular beam epitaxy. We show that with zero- and one-dimensional quantum structures, superior magnetic properties of MnGe compared with bulk films can be obtained. More importantly, with MnGe nanostructures, such as quantum dots, we demonstrate a field-controlled ferromagnetism up to 100K. The controllability of ferromagnetism in this material system presents a major step towards Ge based spintronic devices working at ambient temperatures.