The layers of a high-temperature novel GaAs:Fe diluted magnetic semiconductor (DMS) with an average Fe content up to 20 at. % were grown on (001) i-GaAs substrates using a pulsed laser deposition in ...a vacuum. The transmission electron microscopy (TEM) and energy-dispersive x-ray spectroscopy investigations revealed that the conductive layers obtained at 180 and 200 ºC are epitaxial, do not contain any second-phase inclusions, but contain the Fe-enriched columnar regions of overlapped microtwins. The TEM investigations of the non-conductive layer obtained at 250 ºC revealed the embedded coherent Fe-rich clusters of GaAs:Fe DMS. The x-ray photoelectron spectroscopy investigations showed that Fe atoms form chemical bonds with Ga and As atoms with almost equal probability and thus the comparable number of Fe atoms substitute on Ga and As sites. The n-type conductivity of the obtained conductive GaAs:Fe layers is apparently associated with electron transport in a Fe acceptor impurity band within the GaAs band gap. A hysteretic negative magnetoresistance (MR) was observed in the conductive layers up to room temperature (RT). MR measurements point to the out-of-plane magnetic anisotropy of the conductive GaAs:Fe layers related to the presence of the columnar regions. The studies of the magnetic circular dichroism confirm that the layers obtained at 180, 200 and 250 ºC are intrinsic ferromagnetic semiconductors and the Curie point can reach up to at least RT in case of the conductive layer obtained at 200 ºC. It was suggested that in heavily Fe-doped GaAs layers the ferromagnetism is related to the Zener double exchange between Fe atoms with different valence states via an intermediate As and Ga atom.
Results are presented from measuring the
cross section and effective neutron timelike form factor. Data are collected in 2020–2021 at the VEPP-2000
collider in the 1891 to 2007 MeV center-of-mass ...range of energies. The general purpose nonmagnetic SND detector is used to detect neutron–antineutron events. The time-of-flight approach is used to select
events. The measured cross section is 0.4–0.6 nbn. The neutron form factor in the investigated range of energies varies from 0.3 to 0.2.
The prototype of polarized deuteron source was made for the Van de Graaff accelerator of the Czech Technical University in Prague with aim to create full scale setup for producing polarized neutron ...beam for experiments on measurement
and
, longitudinal and transversal spin asymmetries in transmission polarized neutron beam through frozen polarized deuteron target. It is based on Kaminsky’s experiment on channeling deuterons through a magnetized Ni single crystal foil of 1–2 μm. It is proposed to use the reaction T
He with polarized deuterons of an energy 150–200 keV. For a nonchanneled beam (the goniometer in a random position), the tensor polarization measurements were carried out with a TiT target. Our result is
. This result indicates that deuterium atoms that have passed outside the channels also become polarized due to the capture of polarized electrons from the nickel crystal.
A
bstract
The cross section of the process
e
+
e
−
→
π
+
π
−
has been measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2000
e
+
e
−
collider VEPP-2000 in the energy region 525
...<
s
<
883 MeV. The measurement is based on data with an integrated luminosity of about 4.6 pb
−
1
. The systematic uncertainty of the cross section determination is 0.8% at
s
>
0
.
600 GeV. The
ρ
meson parameters are obtained as
m
ρ
= 775
.
3 ± 0
.
5 ± 0
.
6 MeV, Γ
ρ
= 145
.
6 ± 0
.
6 ± 0
.
8 MeV,
B
ρ
→
e
+
e−
×
B
ρ
→
π
+
π−
= (4
.
89 ± 0
.
02 ± 0
.
04) × 10
−
5
, and the parameters of the
e
+
e
−
→
ω
→
π
+
π
−
process, suppressed by
G
-parity, as
B
ω
→
e
+
e−
×
B
ω
→
π
+
π−
= (1
.
32 ± 0
.
06 ± 0
.
02) × 10
−
6
and and
ϕ
ρω
= 110
.
7 ± 1
.
5 ± 1
.
0 degrees.
•Ion irradiation of (In,Fe)Sb allows to control carrier density and Fermi level position.•Ion irradiation of (In,Fe)Sb leads to conductivity type conversion from n- to p-type.•Magnetic properties of ...(In,Fe)Sb are resistant to changes of carrier density and Fermi level position.
The influence of He+ ion irradiation on magnetotransport properties of epitaxial layers of a diluted magnetic semiconductor (DMS) (In,Fe)Sb, a two-phase (In,Fe)Sb composite and a nominally undoped InSb semiconductor has been investigated. In all layers, a conductivity type conversion from the initial n-type to the p-type has been found. The ion fluence at which the conversion occurs depends on the Fe concentration in the InSb matrix. Magnetotransport properties of the two-phase (In,Fe)Sb layer are strongly affected by ferromagnetic Fe inclusions. An influence of the number of electrically active radiation defects on the magnetic properties of the single-phase In0.75Fe0.25Sb DMS has been found. At the same time, the results show that the magnetic properties of the In0.75Fe0.25Sb DMS are quite resistant to significant changes of the charge carrier concentration and the Fermi level position. The results confirm a weak interrelation between the ferromagnetism and the charge carrier concentration in (In,Fe)Sb that is fundamentally different from Mn doped III-V DMS.
Study of the Process in the Energy Range GeV Achasov, M. N.; Barnyakov, A. Yu; Beloborodov, K. I. ...
Physics of atomic nuclei,
2023/12, Letnik:
86, Številka:
6
Journal Article
Recenzirano
The
cross section is measured in the center-of-mass energy range from 1.07 to 2.00 GeV in the decay channel
,
. The data set with an integrated luminosity of 242 pb
accumulated in the experiment with ...the SND detector at the VEPP-2000
collider is analyzed.
•Mn δ-doped GaAs structures have two parallel conduction channels (VB and IB).•Ferromagnetic properties of Mn δ-doped structures determined by electrons within IB.•A quantum well near Mn δ-layer has ...no influence on ferromagnetic properties.
We investigate the nature of transport and ferromagnetic properties of the epitaxial GaAs structure with the Mn δ-doped layer. To modify the properties of the structure electrically active radiation defects are created by irradiation with 50 keV helium ions and a fluence in the range of 1 × 1011–1 × 1013 cm−2. The investigations show that transport properties of the structure are determined by two parallel conduction channels (the channel associated with hole transport in a valence band and the channel associated with electron transport in the Mn-related impurity band) and that ferromagnetic properties are determined by electrons localized at allowed states within the Mn impurity band. The ferromagnetic properties of the Mn δ-layer region cannot be affected by the closely located InGaAs quantum well, since the presence of quantum well has negligible influence on the Mn impurity band filling by electrons.
The process
e
+
e
-
→
η
η
γ
is studied in the center-of-mass energy range 1.17–2.00 GeV using data with an integrated luminosity of 201 pb
-
1
collected by the SND detector at the VEPP-2000
e
+
e
-
...collider. The
e
+
e
-
→
η
η
γ
cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the
ϕ
η
intermediate state. Our result on the
e
+
e
-
→
η
η
γ
cross section is consistent with the
e
+
e
-
→
ϕ
η
measurement in the
ϕ
→
K
+
K
-
mode. The search for radiative processes contributing to the
e
+
e
-
→
η
η
γ
cross section is performed, and no significant signal is observed.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Search for the process e + e − → η Achasov, M. N.; Barnyakov, A. Yu; Beloborodov, K. I. ...
Physical review. D,
09/2018, Letnik:
98, Številka:
5
Journal Article
Recenzirano
Odprti dostop
A search for the rare decay η→e+e− is performed using the inverse process e+e−→η in the decay mode η→π0π0π0. We analyze data with an integrated luminosity of 654 nb−1 accumulated at the VEPP-2000 ...e+e− collider with the SND detector at the center-of-mass energy E=mηc2≈548 MeV, and set the upper limit B(η→e+e−)<7×10−7 at the 90% confidence level.
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