Research Topics

Spintronics

The mainstream research activities in the field of STT-MRAM is to use CoFeB as a magnetic storage material with a MgO barrier to form an magnetic tunnel junction (MTJ) structure as it can provide the highest TMR with PMA. However, as PMA is induced from the interface between CoFeB electrode and MgO barrier, an ultrathin (<1.8 nm) CoFeB thin film has to be employed. As a result, current CoFeB-based STT-MRAM suffers from the low thermal stability, determined by the product of the thermal energy barrier and the volume of the storage layer, when it is scaled down to 50 nm. In addition, it is reported that CoFeB film has an increasing damping constant as its thickness decreases below 2 nm. The increased damping constant will reduce the figure of merit defined by the ratio of thermal energy barrier to the writing current. An ideal material would provide high PMA to ensure a sufficient thermal energy barrier, low damping constant and structurally match with MgO barrier for a high TMR ratio. Some of the promising candidates known so far are the Heusler alloys, MnxGa and Mn3Ge. Therefore, we explore the use of Heusler alloys, MnxGa or Mn3Ge to completely replace CoFeB or as part of storage layer structure such as CoFeB/MnxGa electrode.

 

Magneto-transport studies of magnetic semiconductors under high pressure

The influence of pressure experiments on pure and applied studies of semiconductors is significant especially in explaining and predicting the physical properties. When we squeeze a solid hydrostatically (isotropic directions), the separations of the atoms can decrease. This will affect the electronic structure, vibrational structure, and how the electrons would interact with the lattice vibrations. The most fascinating effect is that pressure can change semiconductor band gaps and this completely changes the response of the semiconductor. Hence pressure can be used as an exquisite tool to study band gaps. We have reported the studies of magnetotransport properties of p-type Ge0.9Mn0.1Te under hydrostatic pressure which discussed the factors that influence the RKKY interaction.