Currently, my group consists of ten people and we mainly focus on the following 4 topics:
1. Topological magnetic skyrmion creation and manipulation
[theory and experiment]
One of the most heavily researched topics in solid state physics and nanomagnetism
in recent years is a
particle-like topological soliton — magnetic skyrmion which is promising for ultradense information storage and
spin logic devices applications. The interests in skyrmions continue to rapidly increase as evidenced by a
number of publications in high impact factor journals in 2014.
2. Spin torque oscillator for wireless communication [Experiment]
Spin torque oscillator (STO) based RF technology offers several advantages for a
wide range of wireless
applications. From a commercial point of view, the most intriguing advantage is the possibility to generate a
high-quality RF oscillation without the need for large on-chip inductors. Since a modern day cell phone
includes a large number of oscillators for various radio standards (Multiband GSM, Bluetooth, WLAN and so
forth), the cost for the inductors makes up a significant part of the total chip cost. Since the STO can be
operated over a wide range of frequencies, a single STO can supply carrier signals to several individual bands.
In addition, the extremely short start-stop times enables fast jumping between bands. We have developed the
home-made macrospin and micromagnetics simulation packages for studying this device. We have also carried out
the simulation and design of STO circuits for satellite, cell phone and vehicle radar systems.
3. Spin torque switching probability for STTRAM application [Experiment]
I have been a visiting researcher of the MRAM team of IBM, working on the switching
probability distribution
of
a novel type of memory - spin transfer torque magnetic RAM (STTRAM), which is based on the recently discovered
spin momentum transfer mechanism. My research at IBM covers the most important aspects of STTRAM, such as
scalability, thermal stability etc. The core of each memory cell in STTRAM is a magnetic tunnel junction (MTJ),
which consists of two thin ferromagnetic layers separated by a non-magnetic insulator as the tunnel barrier. As
the dimension of a MTJ continues to shrink, thermal-driven magnetization fluctuation noise has become a major
concern. Maintaining sufficient thermal stability at room temperature is one of the fundamental challenges for
STTRAM. We have also studied the effect of external field and current-bias on the switching probability in
MgO-based MTJs. This work will provide further understanding of possible mechanisms in determining the
spin-torque-induced switching in MTJs for STTRAM application.
4. Size effect and electric energy harvesting
applications of ferroelectric nanostructures [theory and
modeling]
We have been working on the size dependence of ferroelectric and dielectric
properties, piezoelectric and
pyroelectric response of ferroelectric nanowire and nanotube, and utilizing such nanowire arrays for effective
nanopower sources. In addition, the photoelectricity of the nanosized ferroelectrics has been studied as a
function of external stimuli such as light intensity and applied mechanical stress. More recently, we extended
the theoretical study of ferroelectrics to the multiferroic layered structure. It is found that the strong
coupling of different order parameters such as polarization, mechanical stress, and magnetization in
multiferroic multilayered nanostructures make such systems very appealing for a broad range of applications
such as high-sensitivity electronic, photonic and mechanical sensors.