655 research outputs found
Nanoscale spin-polarization in dilute magnetic semiconductor (In,Mn)Sb
Results of point contact Andreev reflection (PCAR) experiments on (In,Mn)Sb
are presented and analyzed in terms of current models of charge conversion at a
superconductor-ferromagnet interface. We investigate the influence of surface
transparency, and study the crossover from ballistic to diffusive transport
regime as contact size is varied. Application of a Nb tip to a (In,Mn)Sb sample
with Curie temperature Tc of 5.4 K allowed the determination of
spin-polarization when the ferromagnetic phase transition temperature is
crossed. We find a striking difference between the temperature dependence of
the local spin polarization and of the macroscopic magnetization, and
demonstrate that nanoscale clusters with magnetization close to the saturated
value are present even well above the magnetic phase transition temperature.Comment: 4 page
Engineering of spin-lattice relaxation dynamics by digital growth of diluted magnetic semiconductor CdMnTe
The technological concept of "digital alloying" offered by molecular-beam
epitaxy is demonstrated to be a very effective tool for tailoring static and
dynamic magnetic properties of diluted magnetic semiconductors. Compared to
common "disordered alloys" with the same Mn concentration, the spin-lattice
relaxation dynamics of magnetic Mn ions has been accelerated by an order of
magnitude in (Cd,Mn)Te digital alloys, without any noticeable change in the
giant Zeeman spin splitting of excitonic states, i.e. without effect on the
static magnetization. The strong sensitivity of the magnetization dynamics to
clustering of the Mn ions opens a new degree of freedom for spin engineering.Comment: 9 pages, 3 figure
Measurement of Spin Polarization by Andreev Reflection in Ferromagnetic In1-xMnxSb Epilayers
We carried out Point Contact Andreev Reflection (PCAR) spin spectroscopy
measurements on epitaxially-grown ferromagnetic In1-xMnxSb epilayers with a
Curie temperature of ~9K. The spin sensitivity of PCAR in this material was
demonstrated by parallel control studies on its non-magnetic analog,
In1-yBeySb. We found the conductance curves of the Sn point contacts with
In1-yBeySb to be fairly conventional, with the possible presence of
proximity-induced superconductivity effects at the lowest temperatures. The
experimental Z-values of interfacial scattering agreed well with the estimates
based on the Fermi velocity mismatch between the semiconductor and the
superconductor. These measurements provided control data for subsequent PCAR
measurements on ferromagnetic In1-xMnxSb, which indicated spin polarization in
In1-xMnxSb to be 52 +- 3%
Incidence of bone formation by whole bone marrow cell suspensions and by its stromal cell cultures injected into kidney parenchyma of Balb/c mice
The evaluation of incidence of bone formation by whole syngeneic bone marrow cell suspension and by bone marrow stromal cell cultured in vitro injection into kidney parenchyma was done. Bone tissue was found in 26 kidneys out of 100 injected with whole bone marrow cells suspension. Cultured stromal bone marrow cells grafted into kidney parenchyma produced ossicles in only 4 out of 101 injected kidneys. Such low incidence of bone forming ability of the marrow stromal cell cultures grafted into kidney indicate their useless for study on bone histogenesis in the kidney by murine marrow stromal cell cultures
Effects of Capping on the (Ga,Mn)As Magnetic Depth Profile
Annealing can increase the Curie temperature and net magnetization in
uncapped (Ga,Mn)As films, effects that are suppressed when the films are capped
with GaAs. Previous polarized neutron reflectometry (PNR) studies of uncapped
(Ga,Mn)As revealed a pronounced magnetization gradient that was reduced after
annealing. We have extended this study to (Ga,Mn)As capped with GaAs. We
observe no increase in Curie temperature or net magnetization upon annealing.
Furthermore, PNR measurements indicate that annealing produces minimal
differences in the depth-dependent magnetization, as both as-grown and annealed
films feature a significant magnetization gradient. These results suggest that
the GaAs cap inhibits redistribution of interstitial Mn impurities during
annealing.Comment: 12 pages, 3 figures, submitted to Applied Physics Letter
Fractional quantum Hall effect in CdTe
The fractional quantum Hall (FQH) effect is reported in a high mobility CdTe
quantum well at mK temperatures. Fully-developed FQH states are observed at
filling factor 4/3 and 5/3 and are found to be both spin-polarized ground state
for which the lowest energy excitation is not a spin-flip. This can be
accounted for by the relatively high intrinsic Zeeman energy in this single
valley 2D electron gas. FQH minima are also observed in the first excited (N=1)
Landau level at filling factor 7/3 and 8/3 for intermediate temperatures.Comment: Submitte
Influence of exciton spin relaxation on the photoluminescence spectra of semimagnetic quantum dots
We present a comprehensive experimental and theoretical studies of
photoluminescence of single CdMnTe quantum dots with Mn content x ranging from
0.01 to 0.2. We distinguish three stages of the equilibration of the exciton-Mn
ion spin system and show that the intermediate stage, in which the exciton spin
is relaxed, while the total equilibrium is not attained, gives rise to a
specific asymmetric shape of the photoluminescence spectrum. From an excellent
agreement between the measured and calculated spectra we are able to evaluate
the exciton localization volume, number of paramagnetic Mn ions, and their
temperature for each particular dot. We discuss the values of these parameters
and compare them with results of other experiments. Furthermore, we analyze the
dependence of average Zeeman shifts and transition linewidths on the Mn content
and point out specific processes, which control these values at particular Mn
concentrations.Comment: submitted to Phys. Rev.
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