New frontiers of oxide electronics: correlation between electrical,magnetic and optical properties of oxide semiconductors
                    Dr. Antonio Ruotolo
Department of Physics and Materials Science, City University of Hong Kong
To combine electronics, magnetics, and photonics for next generation multifunctional
devices, it is essential to search for magnetic semiconductor materials with correlated
properties. Here we present examples of systems in which one between electrical, magnetic
or optical properties can be tuned by changing the others.
Non-volatile electrical control of magnetism was, for instance, engineered in Mnsubstituted
ZnO [1,2] and NiO [3]. We show that the magnetic properties of these two
simple semiconductor oxides can be altered in a reversible and non-volatile manner by the
application of an electric field. Bipolar resistive memory switching was induced in films
sandwiched between two metallic electrodes. The bistable switching of the resistive state
was accompanied by a bistable switching of the magnetic moment. The scalability of the
system was investigated by fabricating devices with lateral size down to 400 nm.
The optical properties of wide bang gap semiconductors can be tuned by doping with
transition metals. Doping with magnetic ions is expected to widen the band gap and
produce a blue-shift in the emission peak at room temperature. A red shift can be induced
at low temperatures due to the sp-d exchange interaction. We succeeded in doing so for the
first time in Mn-substituted ZnO [4]. In films with low concentration of dopant, increasing
the exchange interaction by increasing the concentration of charge carriers results in a redshift
of the near-band-edge emission peak at room temperature. The expected blue-shift is
recovered upon increasing the concentration of the dopant. The same films show a
surprisingly large negative magneto-resistance at low temperatures. By using magnetophotoluminescence,
we demonstrated that the affect is due to magnetically induced
transition from hopping to band-conduction where the activation energy is caused by sp-d
exchange interaction [5].
[1] X. L. Wang et al., J. Alloys Compd. 542, 147 (2012).
[2] X. L. Wang et al., J. Appl. Phys. 113, 17C301 (2013).
[3] X. L. Wang et al., Appl. Phys. Lett. 103, 223508 (2013).
[4] X. L. Wang et al., Appl. Phys. Lett. 102, 102112 (2013).
[5] X. L. Wang et al., Scintific Reports, 5, 9221 (2015).
Biography
Dr. Ruotolo received his Laurea cum Laude in 2002 from the University of Naples (IT)
“Federico II” with a thesis on superconductivity, under the supervision of Prof. A. Barone.
In 2003 he joined the Dept. of Materials Science of the University of Cambridge (UK),
supported by a European exchange grant. He completed his doctorate in 2006 in Naples
with a thesis on spintronics, in collaboration with the Fiat research center of Turin. In
2007, he became a Research Associate of the Hong Kong Polytechnic University before
receiving a Marie Curie post-doctoral fellowship in the group of the future Nobel Laureate
Prof. Albert Fert in the CNRS/Thales joint laboratory in Paris (FR). He has authored more
than 50 papers in top-tier journals, including Nature Physics, Nature Nanotechnology and
Scientific Reports. He has joined the City University of Hong Kong in October 2009,
where he is currently an Assistant Professor.

时间：2015年3月6日（周五）下午
地点：物理馆106会议室