1,061 research outputs found
Effect of Ga irradiation on magnetic and magnetotransport properties in (Ga,Mn)As epilayers
We report on the magnetic and magnetotransport properties of ferromagnetic
semiconductor (Ga,Mn)As modified by Ga ion irradiation using focused ion
beam. A marked reduction in the conductivity and the Curie temperature is
induced after the irradiation. Furthermore, an enhanced negative
magnetoresistance (MR) and a change in the magnetization reversal process are
also demonstrated at 4 K. Raman scattering spectra indicate a decrease in the
concentration of hole carriers after the irradiation, and a possible origin of
the change in the magnetic properties is discussed
Mixed magnetic phases in (Ga,Mn)As epilayers
Two different ferromagnetic-paramagnetic transitions are detected in
(Ga,Mn)As/GaAs(001) epilayers from ac susceptibility measurements: transition
at a higher temperature results from (Ga,Mn)As cluster phases with [110]
uniaxial anisotropy and that at a lower temperature is associated with a
ferromagnetic (Ga,Mn)As matrix with cubic anisotropy. A change in the
magnetic easy axis from [100] to [110] with increasing temperature can be
explained by the reduced contribution of cubic anisotropy to the magnetic
properties above the transition temperature of the (Ga,Mn)As matrix
Ion Irradiation Control of Ferromagnetism in (Ga,Mn)As
We report on a promising approach to the artificial modification of
ferromagnetic properties in (Ga,Mn)As using a Ga focused ion beam (FIB)
technique. The ferromagnetic properties of (Ga,Mn)As such as magnetic
anisotropy and Curie temperature can be controlled using Ga ion
irradiation, originating from a change in hole concentration and the
corresponding systematic variation in exchange interaction between Mn spins.
This change in hole concentration is also verified using micro-Raman
spectroscopy. We envisage that this approach offers a means of modifying the
ferromagnetic properties of magnetic semiconductors on the micro- or nano-meter
scale.Comment: 4 pages, 4 figures, to appear in Jpn. J. Appl. Phys. (Part 2 Letters
Magnetic anisotropy switching in (Ga,Mn)As with increasing hole concentration
We study a possible mechanism of the switching of the magnetic easy axis as a
function of hole concentration in (Ga,Mn)As epilayers. In-plane uniaxial
magnetic anisotropy along [110] is found to exceed intrinsic cubic
magnetocrystalline anisotropy above a hole concentration of p = 1.5 * 10^21
cm^-3 at 4 K. This anisotropy switching can also be realized by post-growth
annealing, and the temperature-dependent ac susceptibility is significantly
changed with increasing annealing time. On the basis of our recent scenario
[Phys. Rev. Lett. 94, 147203 (2005); Phys. Rev. B 73, 155204 (2006).], we
deduce that the growth of highly hole-concentrated cluster regions with [110]
uniaxial anisotropy is likely the predominant cause of the enhancement in [110]
uniaxial anisotropy at the high hole concentration regime. We can clearly rule
out anisotropic lattice strain as a possible origin of the switching of the
magnetic anisotropy.Comment: 5 pages, 4 figures, to appear in Phys. Rev.
Dynamic relaxation of magnetic clusters in a ferromagnetic (Ga,Mn)As epilayer
A new scenario of the mechanism of intriguing ferromagnetic properties in
Mn-doped magnetic semiconductor (Ga,Mn)As is examined in detail. We find that
magnetic features seen in zero-field cooled and field cooled magnetizations are
not interpreted with a single domain model [Phys. Rev. Lett. 95, 217204
(2005)], and the magnetic relaxation, which is similar to that seen in magnetic
particles and granular systems, is becoming significant at temperatures above
the lower-temperature peak in the temperature dependence of ac susceptibility,
supporting the cluster/matrix model reported in our previous work [Phys. Rev.
Lett. 94, 147203 (2005)]. Cole-Cole analysis reveals that magnetic interactions
between such (Ga,Mn)As clusters are significant at temperatures below the
higher-temperature peak in the temperature dependent ac susceptibility. The
magnetizations of these films disappear above the temperature showing the
higher-temperature peak, which is generally referred to as the Curie
temperature. However, we suggest that these combined results are evidence that
the temperature is actually the blocking temperature of (Ga,Mn)As clusters with
a relatively high hole concentration compared to the (Ga,Mn)As matrix.Comment: 8 pages, 7 figures, to appear in Phys. Rev.
Studies on the prevention of aerobic spoilage of silage by killer yeast, Kluyveromyces lactis
Enhanced animal production systems to satisfy demand for high value animal protein are needed.The driving force behind the demand for livestock products is a combination of population growth (1.5 percent per year),rising incomes (capita GDP has grown over 3 percent per year) ...Thesis (Ph. D. in Agriculture)--University of Tsukuba, (B), no. 1607, 2000.3.24Includes bibliographical references (p. 88-97)Titlepage,Contents -- Chapter.1 Introduction -- Chapter.2 Materials and Methods -- Chapter.3 Development of methods for this study -- Chapter.4 Selection of killer yeasts(Kluyveromyces lactis) to prevent aerobic spoilage of silage -- Chapter.5 lsolation of Kluyveromyces lactis killer strain defective in growth on lactic acid -- Chapter.6 Prevention of aerobic spoilage of maize silage by a genetically modified killer yeast,defective in ability to grow on lactic acid -- Chapter.7 Safety aspect of using a genetically modified strain as a silage additive -- Chapter.8 General Discussion -- Acknowledgments,References,Paper list
Energy Spectra and Normalized Power Spectral Densities of X-Ray Nova GS 2000+25
The X-ray energy spectra and Normalized Power Spectral Densities (NPSDs) of
an X-ray nova, GS 2000+25, were investigated. The X-ray energy spectra of the
source consist of two components: a hard component, which can be represented by
a power-law, and an ultra-soft component, represented by radiation from an
optically-thick accretion disk (the disk component). In a model in which the
power-law component is the Compton-scattered radiation, it is found that the
temperature of the incident blackbody radiation to the Compton cloud decrease
from 0.8 keV to 0.2 keV according to the decay of the intensity, which
coincides with that of the inner accretion disk. When the source changed from
the high-state to the low-state, both the photon index of the power-law
component (or Compton y-parameter) and the NPSD of the hard component
dramatically changed as did GS 1124-683. That is, the photon index changed from
2.2--2.6 to 1.7--1.8 and the absolute values of the NPSDs at 0.3 Hz of the hard
component in the low-state became about 10-times larger than those of the hard
component in the high-state. These X-ray properties were similar to those of
other black-hole candidates, such as Cyg X-1, GX 339-4, and LMC X-3.Comment: 24 pages, text only, Full version is published in PASJ 54, 609-627
(2002
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