5 research outputs found
Dynamics of electronic transitions and frequency dependence of negative capacitance in semiconductor diodes under high forward bias
We observed qualitatively dissimilar frequency dependence of negative capacitance under high charge injection in two sets of functionally different junction diodes: III-V based light emitting and Si-based non-light emitting diodes. Using an advanced approach based on bias activated differential capacitance, we developed a generalized understanding of negative capacitance phenomenon which can be extended to any diode based device structure. We explained the observations as the mutual competition of fast and slow electronic transition rates which are different in different devices. This study can be useful in understanding the interfacial effects in semiconductor heterostructures and may lead to superior device functionality
On Using Magnetic and optical methods to determine the size and characteristics of nanoparticles embedded in oxide semiconductors
Films of oxides doped with transition metals are frequently believed to have
magnetic inclusions. Magnetic methods to determine the amount of nanophases and
their magnetic characteristics are described. The amount of the sample that is
paramagnetic may also be measured. Optical methods are described and shown to
be very powerful to determine which defects are also magnetic.Comment: Manuscript of poster to be presented at MMM-Intermag 2010. Accepted
for publication in Magnetic Trans of IEE
Magnetic and Optical properties of strained films of multiferroic GdMnO3
The effects of strain on a film of mulitferroic GdMnO3 are investigated using
both magnetometry and magneto-optic spectroscopy. Optical spectra, in the
energy range 1.5eV - 3.5eV, were taken in Faraday geometry in an applied
magnetic field and also at remanence. This yielded rich information on the
effects of strain on the spin ordering in these films. Epitaxial films of
GdMnO3 were grown on SrTiO3 and LaAlO3 substrates. The LaAlO3 was twinned and
so produced a highly strained film whereas the strain was less for the film
grown on SrTiO3. The Ne\'el temperatures and coercive fields were measured
using zero field data and hysteresis loops obtained using a SQUID magnetometer.
Optical absorption data agreed with earlier work on bulk materials. The two
well known features in the optical spectrum, the charge transfer transition
between Mn d states at ~2eV and the band edge transition from the oxygen p band
to the d states at ~3eV are observed in the magnetic circular dichroism;
however they behaved very differently both as a function of magnetic field and
temperature. This is interpreted in terms of the magnetic ordering of the Mn
spins.Comment: 9 pages of text including figure
Magneto-optical properties of Co/ZnO multilayer films
Multilayer films of ZnO with Co were deposited on glass substrates then
annealed in a vacuum. The magnetisation of the films increased with annealing
but not the magnitude of the magneto-optical signals. The dielectric functions
for the films were calculated using the MCD spectra. A Maxwell Garnett theory
of a metallic Co/ZnO mixture is presented. The extent to which this explains
the MCD spectra taken on the films is discussed.Comment: This paper was presented at ICM (2009) and is accepted in this form
for the proceeding
Enhanced magnetic properties in ZnCoAlO caused by exchangecoupling to Co nanoparticles
We report the results of a sequence of magnetisation and magneto-optical studies on laser ablated thin films of ZnCoAlO and ZnCoO that contain a small amount of metallic cobalt. The results are compared to those expected when all the magnetization is due to isolated metallic clusters of cobalt and with an oxide sample that is almost free from metallic inclusions. Using a variety of direct magnetic measurements and also magnetic circular dichroism we find that there is ferromagnetism within both the oxide and the metallic inclusions, and furthermore that these magnetic components are exchange-coupled when aluminium is included. This enhances both the coercive field and the remanence. Hence the presence of a controlled quantity of metallic nanoparticles in ZnAlO can improve the magnetic response of the oxide, thus giving great advantages for applications in spintronics