Theoretical investigation on the phase stability of Nd2Fe14B and site preference of V, Cr, Mn, Zr and Nb

The stability of the excellent permanent magnetic compound Nd2Fe14B and substitution of Fe in the compound by V, Cr, Mn, Zr and Nb are investigated by using interatomic pair potentials which are converted from lattice-inversion method. Calculation shows that the substitution always makes the cell volume larger, and the increase of the volume is almost linear with substituent concentration. The calculated cohesive energy shows that the preferential order of substitution of Fe is Nb, V, Cr, Mn, Zr. Nevertheless, all the five substituting elements should most preferentially replace Fe in the j(2)' site, which has the greatest space among all six Fe sites. (C) 2005 Elsevier B.V. All rights reserved.

Gal(1-x)Mn(1-x)Sb grown on GaSb with mass-analyzed low-energy dual ion beam deposition

The Ga1-xMnxSb samples were fabricated by the implantation of Mn ions into GaSb (1 0 0) substrate with mass-analyzed low-energy dual ion beam deposition system, and post-annealing. Auger electron spectroscopy depth profile of the Ga1-xMnxSb samples showed that the Mn ions were successfully implanted into GaSb substrate. Clear double-crystal X-ray diffraction patterns of the Ga1-xMnxSb samples indicate that the Ga1-xMnxSb epilayers have the zinc-blende structure without detectable second phase. Magnetic hysteresis-loop of the Ga1-xMnxSb epilayers were obtained at room temperature (293 K) with alternating gradient magnetometry. (c) 2005 Elsevier B.V. All rights reserved.

Concentration effect of Mn2+ on the photoluminescence of ZnS : Mn nanocrystals

Mn-doped ZnS nanocrystals of about 3 nm diameter were synthesized by a wet chemical method. X-ray diffraction (XRD) measurements showed that the nanocrystals have the structure of cubic zinc blende. The broadening of the XRD lines is indicative of nanomaterials. Room temperature photoluminescence (PL) spectrum of the undoped sample only exhibited a defected-related blue emission band. But for the doped samples, an orange emission from the Mn2+ T-4(1)-(6)A(1) transition was also observed, apart from the blue emission. The peak position (600 nm) of the Mn2+ emission was shifted to longer wavelength compared to that (584 nm) of bulk ZnS:Mn. With the increase of the Mn2+ concentration, the PL of ZnS:Mn was significantly enhanced. The concentration quenching effect was not observed in our experiments. Such PL phenomena were attributed to the absence of Mn2+ pairs in a single ZnS:Mn nanocrystal, considering the nonradiative energy transfer between Mn2+ ions based on the Poisson approximation. (c) 2005 Elsevier B.V. All rights reserved.

Structural and optical investigation of Mn-doped ZnS nanocrystals

Using a solution-based chemical method, we have prepared ZnS nanocrystals doped with high concentration of Mn2+. The X-ray diffraction analysis confirmed a zinc blende structure. The average size was about 3 nm. Photoluminescence spectrum showed room temperature emission in the visible spectrum, which consisted of the defect-related emission and the T-4(1)-(6)A(1) emission of Mn2+ ions. Compared with the undoped sample, the luminescence of the ZnS:Mn sample is enhanced by more than an order of magnitude, which indicated that the Mn2+ ions can efficiently boost the luminescence of ZnS nanocrystals.

Generation of a supersinglet of three three-level atoms in cavity QED

We propose a scheme to generate a supersinglet of three three-level atoms in microwave cavity quantum electrodynamics based on the resonant atom-cavity interaction. In the scheme, three three-level atoms in suitable initial states are sequentially sent through three cavities originally prepared in their vacuum states. After an appropriate atom-cavity interaction process, in the subsequent measurement on the third cavity field the atoms are projected onto the desired supersinglet. The practical feasibility of this method is discussed.

Investigation of phtoluminesecence under hydrostatic pressure in different sized ZnS : Mn nanoparticles

The PL spectra for the 10, 4. 5, 3. 5, 3, 1 nm sized ZnS:Mn2+ nanoparticles and corresponding bulk material under different pressures were investigated. The orange emission band originated from the T-4(1)-(6)A(1) transition of Mn2+ ions showed obvious red shift with the increasing of pressures. The pressure coefficients of Mn-related emissions measured from bulk, 10, 4. 5, 3.5 and 3 nm samples are -29.4 +/- 0.3, -30.1 +/- 0.3, -33.3 +/- 0.6, -34.6 +/- 0.8 and -39 +/- 1 meV/GPa, respectively. The absolute value of the pressure coefficient increases with the decrease of the size of particles. The size dependence of crystal field strength Dq and Racah parameter B accounts for the size behavior of the Mn-related emission in ZnS:Mn nanoparticles. The pressure behavior of Mn-related emission in the 1 nm sized sample is somewhat different from that of other nanoparticles. It may be due to smaller size of 1 nm sample and the special surface condition since ZnS nanoparticles are formed in the cavities of ziolite-Y for the 1 nm sample.

Ferromagnetism in Mn and Cr doped GaN by thermal diffusion

Doping of magnetic element Mn and Cr in GaN was achieved by thermal diffusion. The conductivity of the samples, which were all n-type, did not change significantly after the diffusion doping. X-ray diffraction measurements revealed no secondary phase in the samples. Experiments using superconducting quantum interference device (SQUID) showed that the samples were ferromagnetic at 5 and 300 K, implying the Curie temperature to be around or over 300 K, despite their n-type conductivity. (c) 2004 Elsevier B.V. All rights reserved.

A convenient way of determining the ferromagnetic transition temperature of metallic (Ga,Mn)As

We have studied magnetic and transport properties of insulating and metallic (Ga,Mn)As layers before and after annealing. A dramatic increase of the ferromagnetic transition temperature T-C by postgrowth annealing has been realized in both insulating and metallic (Ga,Mn)As. The as-grown insulating (Ga,Mn)As can be turned into metallic by the low-temperature annealing. For all the metallic (Ga,Mn)As, a characteristic feature in the temperature dependence of sheet resistance appears around T-C. This phenomenon may provide a simple and more convenient method to determine the T-C of metallic (Ga,Mn)As compared with superconducting quantum interference device (SQUID) measurement. Moreover, the T-C of the metallic (Ga,Mn)As obtained by this way is in good agreement with that measured by a SQUID magnetometer. (C) 2005 American Institute of Physics.

Investigation of Mn-implanted n-Si by low-energy ion beam deposition

Mn ions were implanted to n-type Si(0 0 1) single crystal by low-energy ion beam deposition technique with an energy of 1000 eV and a dose of 7.5 x 10(17) cm(-2). The samples were held at room temperature and at 300degreesC during implantation. Auger electron spectroscopy depth profiles of samples indicate that the Mn ions reach deeper in the sample implanted at 300degreesC than in the sample implanted at room temperature. X-ray diffraction measurements show that the structure of the sample implanted at room temperature is amorphous while that of the sample implanted at 300degreesC is crystallized. There are no new phases found except silicon both in the two samples. Atomic force microscopy images of samples indicate that the sample implanted at 300degreesC has island-like humps that cover the sample surface while there is no such kind of characteristic in the sample implanted at room temperature. The magnetic properties of samples were investigated by alternating gradient magnetometer (AGM). The sample implanted at 300degreesC shows ferromagnetic behavior at room temperature. (C) 2004 Elsevier BN. All rights reserved.

Magnetic properties of Mn-implanted n-type Ge

Mn+ ions were implanted into n-type Ge(1 1 1) single crystal at room temperature at an energy of 100 keV with a dose of 3 x 10(16) cm(-2). Subsequent annealing was performed on the samples at 400 degreesC and 600 degreesC in a flowing nitrogen atmosphere. The magnetic properties of the samples have been investigated by alternating gradient magnetometer at room temperature. The compositional properties of the annealed samples were studied by Auger electron spectroscopy and the structural properties were analyzed by X-ray diffraction measurements. Magnetization measurements reveal room-temperature ferromagnetism for the annealed samples. The magnetic analysis supported by compositional and structural properties indicates that forming the diluted magnetic semiconductor (DMS) MnxGe1-x after annealing may account for the ferromagnetic behavior in the annealed samples. (C) 2004 Elsevier B.V. All rights reserved.

Memory effect in a system of zincblende Mn-rich Mn(Ga)As nanoclusters embedded in GaAs

Zincblende Mn-rich Mn(Ga)As nanoclusters embedded in GaAs matrices are fabricated by in situ postgrowth annealing diluted magnetic semiconductor (Ga,Mn)As films with Mn concentration ranging from 2.6% to 8% at 650 degrees C. Magnetization measurements show that memory effect and slow magnetic relaxation, the typical characteristics of the spin-glass-like phase, occur below the blocking temperature of 45 K in samples with high Mn concentration, while for samples with low Mn concentration, ferromagnetic order remains up to 360 K. The behavior of low-temperature spin dynamics can be explained by the hierarchical model. (c) 2007 American Institute of Physics.

Electrical and optical properties of InAs/GaAs quantum dots doped by high energy Mn implantation

Mn ions were doped into InAs/GaAs quantum dots samples by high energy. implantation and subsequent annealing. The optical and electric properties of the samples have been studied. The photoluminescence intensity of the samples annealed rapidly is stronger than that of the samples annealed for long time. By studying the relationship between the photoluminescence peaks and the implantation dose, it can be found that the photoluminescence peaks of the quantum dots show a blueshift firstly and then move to low energy with the implantation. dose increasing. The latter change in the photoluminescence peaks is probably attributed to that Mn ions entering the InAs quantum dots, which release the strain of the quantum dots. For the samples implanted by heavy dose (annealed rapidly) and the samples annealed for long time, the resistances versus temperature curves reveal anomalous peaks around 40 K.

Electronic structure of Mn-doped ZnO quantum wires: A mean-field theory study

Based on the effective-mass model and the mean-field approximation, we investigate the energy levels of the electron and hole states of the Mn-doped ZnO quantum wires (x=0.0018) in the presence of the external magnetic field. It is found that either twofold degenerated electron or fourfold degenerated hole states split in the field. The splitting energy is about 100 times larger than those of undoped cases. There is a dark exciton effect when the radius R is smaller than 16.6 nm, and it is independent of the effective doped Mn concentration. The lowest state transitions split into six Zeeman components in the magnetic field, four sigma(+/-) and two pi polarized Zeeman components, their splittings depend on the Mn-doped concentration, and the order of pi and sigma(+/-) polarized Zeeman components is reversed for thin quantum wires (R < 2.3 nm) due to the quantum confinement effect.

Influences of As flux on the lattice constants, magnetic and transport properties of (Ga, Mn)As epilayers

A series of (Ga, Mn)As epilayers have been prepared on semi-insulating GaAs (001) substrates at 230 degrees C by molecular-beam epitaxy under fixed temperatures of Ga and Mn cells and varied temperatures of the As cell. By systematically studying the lattice constants, magnetic and magneto-transport properties in a self-consistent manner, we find that the concentration of As antisites monotonically increases with increasing As flux, while the concentration of interstitial Mn defects decreases with it. Such a trend sensitively affects the properties of (Ga, Mn)As epilayers. (c) 2006 Elsevier Ltd. All rights reserved.

Electronic noise of diluted magnetic semiconductor (Ga,Mn)As around Curie point

National Natural Science Foundation of China 10674129