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1.
A new spintronics material with the Curie temperature above room temperature, the ZnSiAs2 chalcopyrite doped with 1 and 2 wt % Mn, is synthesized. The magnetization, electrical resistivity, magnetoresistance, and the Hall effect of these compositions are studied. The temperature dependence of the electrical resistivity follows a semiconducting pattern with an activation energy of 0.12–0.38 eV (in the temperature range 124 K ≤ T ≤ 263 K for both compositions). The hole mobility and concentration are 1.33, 2.13 cm2/V s and 2.2 × 1016, 8 × 1016 cm−3 at T = 293 K for the 1 and 2 wt % Mn compositions, respectively. The magnetoresistance of both compositions, including the region of the Curie point, does not exceed 0.4%. The temperature dependence of the magnetization M(T) of both compositions exhibits a complicated character; indeed, for T ≤ 15 K, it is characteristic of superparamagnets, while for T > 15 K, spontaneous magnetization appears which correspond to a decreased magnetic moment per formula unit as compared to that which would be observed upon complete ferromagnetic ordering of Mn2+ spins or antiferromagnetic ordering of spins of the Mn2+ and Mn3+ ions. Thus, for T > 15 K, it is a frustrated ferro- or ferrimagnet. It is found that, unlike the conventional superparamagnets, the cluster moment μ c in these compositions depends on the magnetic field: ∼12000–20000μB for H = 0.1 kOe, ∼52–55μB for H = 11 kOe, and ∼8.6–11.0μB at H = 50 kOe for the compositions with 1 and 2 wt % Mn, respectively. The specific features of the magnetic properties are explained by the competition between the carrier-mediated exchange and superexchange interactions.  相似文献   

2.
    
《Il Nuovo Cimento C》1984,7(6):604-610
Summary The temperature of protons, α particles, silicon and iron ions in the solar wind have been determined analysing 140 energy spectra measured aboard the ISEE-2 spacecraft during 1978 and 1979. The data cover the range of proton temperaturesT p from 104 K to 105 K, never explored in detail before. The experimental results show that in this range of temperatures and for solar-wind velocitiesv sw smaller than 370 km s−1, the temperature of the α-particlesT α is smaller thanT p.T α actually increases faster thanT p withv sw; however, forv sw≤420 km s−1 the ratioT α/T p is always less than 4, while previous observations at higher temperatures (105 K to 106 K) are consistent with a constant ratioT α/T p=4. The temperature of the silicon ions, moreover, tends to become independent ofT p for proton temperatures greater than 3·104 K. Paper presented at the 2o Convegno Nazionale di Fisica Cosmica, held at L'Aquila, 29 May–2 June 1984.  相似文献   

3.
Krishnamurthy  V. V.  Watanabe  I.  Nagamine  K.  Kitagawa  J.  Ishikawa  M.  Komatsubara  T. 《Hyperfine Interactions》2001,136(3-8):385-389
Magnetic and quadrupolar ordering phenomena in a Ce3Pd20Ge6 single crystal have been investigated by muon spin rotation/relaxation (μ+SR) spectroscopy. We have observed spontaneous precession of muons in zero-field below T N =0.7 K in the antiferromagnetic state. The precession frequency follows the power law: ν(T)=ν(0)(1−T/T N ) n . The exponent n=0.43(2) is close to the mean-field value of 0.5. The muon longitudinal spin relaxation rate 1/T 1 is found to be nearly independent of temperature in the range of 0.3 to 2 K, i.e., across either T N or T Q =1.2 K, the quadrupolar ordering temperature. Two likely mechanisms for the temperature independent behavior of 1/T 1 are suggested. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

4.
The dielectric properties, X-ray emission spectra, and M?ssbauer effect in ceramics made of PbFe1/2Nb1/2O3 (PFN) compound were studied. The relaxation dynamics revealed above Curie temperature TC at a frequency of 3 × 10−2–105 Hz is described in detail. Analysis of the X-ray emission and M?ssbauer spectra showed that at room temperature (T = 300 K), the iron ions in PFN are mainly in the high-spin valence state Fe3+. The M?ssbauer spectral parameters obtained at T = (300, 353, and 393 K) indicate an octahedral environment for Fe3+ in both the ferroelectric and paraelectric phases.  相似文献   

5.
BiFeO3 (BFO) ceramics were prepared by a modified solid-state-reaction method which adopts a higher heating/cooling rate during the sintering process than usually used. It was found that the calcination temperature T cal (from 400 to 750°C) does not influence the BFO phase formation, while the sintering temperature T sin (from 815 to 845°C) dominates the phase purity. The optimum sintering temperature was in the range from 825 to 835°C. The optimized samples exhibit saturated ferroelectric hysteresis loops with a remnant polarization of 13.2 μC/cm2. The measured piezoelectric coefficient d 33 was 45 pC/N. No remnant magnetization was observed in all of the samples. The pyroelectric properties were studied as a function of temperature and frequency. A pyroelectric coefficient as high as 90 μC/m2 K was obtained at room temperature in the optimized sample. An abrupt decrease of the pyroelectric coefficient was observed at temperatures between 70 and 80°C. On the basis of our results, BFO may have the potential for pyroelectric applications.  相似文献   

6.
The half-life of the β -decay of 198Au has been measured for room temperature and 12K. The resulting values of T 1/2 (RT) = 2.684±0.004 d and T 1/2 (12K) = 2.687±0.005 d agree well within statistical uncertainties. Evidence for the temperature dependence of the half-life was not observed.  相似文献   

7.
The electroluminescent characteristics of an InGaAsSb/GaAlAsSb heterostructure LED emitting at 1.85 μm are studied in the temperature range 20–200°C. It is shown that the emission power exponentially drops as P ≅ 0.4exp(2.05 × 103/T) with a rise in temperature primarily because of an increase in the Auger recombination rate. It is found that band-to-band radiative recombination goes in parallel with recombination through acceptor levels, the latter causing the emission spectrum to broaden. With a rise in temperature, the activation energy of the acceptor levels decreases by the law ΔE≅ 32.9 − 0.075T and the maximum of the LED’s emission spectrum shifts toward the long-wavelength range ( max = 0.693 − 4.497 × 10−4 T). Based on the dependence E g = max − 0.5kT and experimental data, an expression is derived for the temperature variation of the bandgap in the In0.055Ga0.945AsSb active area, E g ≅ 0.817 − 4.951 × 10−4 T, in the range 290 K < T < 495 K. The resistance of the heterostructure decreases exponentially with rising temperature as R 0 ≅ 5.52 × 10−2exp(0.672/2kT), while cutoff voltage U cut characterizing the barrier height of a p−n junction decreases linearly with increasing temperature (U cut = −1.59T + 534). It is found that the current through the heterostructure is due to the generation-recombination mechanism throughout the temperature interval.  相似文献   

8.
Electrical resistivity ρ and Hal coefficient R are measured as a function of the temperature (T = 1.7−310 K) and the magnetic field (up to H = 28 kOe) in zero-gap semiconductor CuFeS2 samples subjected to hydrostatic compression and under various heat-treatment conditions. At low temperatures, anomalies are observed in the kinetic effects related to the presence of ferromagnetic clusters: the magnetoresistance at T = 4.2 K and T = 20.4 K acquires a hysteretic character and thermopower α changes its sign at T < 15 K. The temperature dependence of conduction-electron concentration n in CuFeS2 has a power form in the temperature range T = 14−300 K, which is characteristic of the intrinsic conductivity in zero-gap semiconductors. In CuFeS2, we have n(T) ∝ T 1.2; in isoelectron compound Cu1.13Fe1.22Te2, we have n(T) ∝ T 1.93. Heat treatment is found to affect the intrinsic conductivity of CuFeS2, as the action of hydrostatic compression (carrier concentration changes); that is, the carrier concentration changes. However, a power form of the n(T) and ρ(T) dependences is retained.  相似文献   

9.
In the present paper, Pb(Mg1/3Nb2/3)O3 (PMN) ceramics prepared by the columbite method were investigated. The dielectric study indicates typical relaxor properties, with a frequency dispersion in the range of 200–350 K. The relaxor-to-paraelectric phase transition was evidenced by the continuous decrease of the local order parameter derived from the permittivity-temperature data. As a result of the critical behavior, the main Raman modes show anomalies at: (i) ∼150 K; (ii) ∼220 K (i.e. close to the critical temperature reported for the field-induced ferroelectric state in PMN single crystal); (iii) ∼260 K (i.e. the temperature of the permittivity maximum); (iv) ∼350 K (the temperature for initiation of the cluster freezing process T *); (v) ∼620 K (Burns temperature). The frequency split of the doublet at ∼605 and ∼500 cm−1 presents a critical behavior related to the local symmetry lowering and to the structure ordering due to a phase transformation which takes place below T *. The tunability in the paraelectric state was interpreted in terms of reorientation of the non-interacting nanopolar clusters in a double-well potential. The temperature dependence of the nanopolar domain size also shows anomalies in the range of T *. The size and dynamics of the polar nanodomains is essential in determining the functional properties of the Pb(Mg1/3Nb2/3)O3 relaxor.  相似文献   

10.
We report measurements of the temperature dependence of the electrical resistivity, ρ(T), and magnetic pen-etration depth, λ(T), for polycrystalline samples of Eu0.5K0.5Fe2As2 with T c = 31 K. ρ(T) follows a linear temperature dependence above T c and bends over to a weaker temperature dependence around 150 K. The magnetic penetration depth, determined by radio frequency technique displays an unusual minimum around 4 K which is associated with short-range ordering of localized Eu3+ moments. The article is published in the original.  相似文献   

11.
Europium oxide (Eu2O3) substituted compound has been prepared by solid-solid reaction of the powders of Eu2O3, BaCO3 and CuO at 950°C for 16 hours. The thin films have been deposited by high vacuum evaporation technique (vacuum ≈ 10−6 torr). The variation of current (I) with voltage (V) at room temperature (RT) i.e. 294 K and in ice (273 K) are found to be linear. The variation of electrical resistivity (ρ) with temperature (T) by heating the sample above RT has been determined. Resistivity is found to decrease with increase in temperature. Further the variation of electrical resistivity (ρ) with temperature (T) from 77 K, liquid nitrogen temperature (LNT), to 270 K has also been determined. It is observed that resistivity suddenly becomes zero at around 87 K. Thus the prepared material has superconducting properties with superconducting transition temperature, T c at 87 K.   相似文献   

12.
13.
A detailed study on the weak localization phenomenon vis-a-vis electron-electron interaction effects in magnetic metallic glasses has been carried out. We measured the electrical conductivity and magnetoconductivity within the temperature range 1.8≤T≤300K. A maximum on the conductivity versus temperature curve exists atT=T m. The conductivity was observed to follow aT 1/2 law forT<T m andT 2 law forT>T m. Magnetoconductivity data of these alloys indicate the prominence of electron-electron interaction at low temperatures. The authors have determined the inelastic scattering field and spin-orbit scattering field from the magnetoconductivity data. The inelastic scattering field obeys aT p law (p=2) at low temperatures.  相似文献   

14.
Charge fluctuations in quasi-one-dimensional hole-doped Sr14Cu24O41 (Ca-0) and Sr2Ca12Cu24O41 (Ca-12) spin-ladder cuprates have been studied with the use of 63Cu-17O NMR. Spin-echo decay rates 17(1/T 2) and 63(1/T 2) have been measured in the temperature range of T = 10–300 K. The variation of 17(1/T 2) and 63(1/T 2) in the Ca-0 compound is monotonic in the entire temperature range of the NMR study. In the Ca-rich compound, pronounced peaks have been observed in the decay rates 17(1/T 2) and 63(1/T 2) at temperatures of 25 and 50 K, respectively. This result indicates the presence of collective low-frequency (τcT 2) charge density fluctuations in superconducting Ca-12 with an activation energy of E A = 100(10) K. The fluctuations gradually slow down as the temperature decreases. The amplitude of the charge density fluctuations is only 0.01–0.02 hole per site. 17O-63Cu spin-echo double-resonance (SEDOR) experiments in Sr14 − x Ca x Cu24O41 oxides with x = 0 and 12 have been performed depending on the temperature and orientation of single crystals in a magnetic field. The constants of an indirect heteronuclear 17O-63Cu interaction of nuclear spins mediated by conduction electrons have been measured. The estimates of the indirect interaction constants for nearest neighbors O1-Cu and O2-Cu, as well as SEDOR experiments with selective excitation of separate sections of 17O and 63Cu NMR spectra, provide convincing evidence of the microscopically inhomogeneous spatial distribution of spin density developing in a crystal. Original Russian Text ? Yu.V. Piskunov, V.V. Ogloblichev, S.V. Verkhovsky, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 11, pp. 850–855.  相似文献   

15.
The effective Debye temperatures Θeff determined for solids by different physical methods have been analyzed and compared. Attention has been focused on the original parameter of the Debye theory of heat capacity, i.e., the translational calorimetric Debye temperature Θ c t (0), and the X-ray Debye temperature Θ x in the framework of the Debye-Waller theory for the C60 fullerite. It has been established that the true Debye law T 3 is satisfied for the C60 fullerite over a very narrow range of temperatures: 0.4 K ≤ T ≤ 1.8 K. For this reason, the experimental Debye temperatures Θ c t (0) obtained for the C60 fullerite by different authors in the range T > 4.2 K are characterized by a large scatter (by a factor of ∼5). It has been revealed that the value Θ c t (0) = 77.12 K calculated in this paper with the use of the six-term Betts formula from the harmonic elastic constants $ \tilde C_{ijkl} $ \tilde C_{ijkl} of the C60 single crystal in the limit T = 0 K is closest to the true Debye temperature. It has been demonstrated using the method of equivalent moments that the real spectral frequency distribution of translational lattice vibrations g(ω) for the C60 fullerite deviates from a parabolic distribution. The effective Debye temperatures Θeff involved in applied problems of thermodynamics of crystals and elastic scattering of different radiations from lattice vibrations have been determined. The quantitative measure of anharmonicity of translational and librational lattice vibrations of the C60 fullerite has been determined. This has made it possible to empirically evaluate the lattice thermal conductivity κ of the C60 fullerite at T ≈ 300 K: κ(300) = 0.80 W (m/K), which is in good agreement with the experimental thermal conductivity κexp = 0.78 W (m/K) at T ≈ 250 K.  相似文献   

16.
The electrical conduction mechanisms in various highly resistive GaN layers of Al x Ga1−x N/AlN/GaN/AlN heterostructures are investigated in a temperature range between T=40 K and 185 K. Temperature-dependent conductivities of the bulk GaN layers are extracted from Hall measurements with implementing simple parallel conduction extraction method (SPCEM). It is observed that the resistivity (ρ) increases with decreasing carrier density in the insulating side of the metal–insulator transition for highly resistive GaN layers. Then the conduction mechanism of highly resistive GaN layers changes from an activated conduction to variable range hopping conduction (VRH). In the studied temperature range, ln (ρ) is proportional to T −1/4 for the insulating sample and proportional to T −1/2 for the more highly insulating sample, indicating that the transport mechanism is due to VRH.  相似文献   

17.
The effect of atomic disorder on the electron transport and the magnetoresistance (MR) of Co2CrAl Heusler alloy (HA) films has been investigated. We show that Co2CrAl films with L21 order exhibit a negative value for the temperature coefficient of resistivity (TCR) in a temperature range of 10 < T < 290 K, and the temperature dependence of electric conductivity varies as T 3/2 similarly to that of the zero-gap semiconductors. The atomic or the site disorder on the way of L21 → B2 → A2 → amorphous state in Co2CrAl HA films causes the deviation from this dependence: reduction in the absolute value of TCR as well as decrease in the resistivity down to ϱ(T = 293 K) ∼ 200 μΩ cm in comparison to ϱ(T = 293 K) ∼ 230 μΩ cm typical for the Co2CrAl films with L21 order. The magnetic-field dependence of MR of the Co2CrAl films with L21 order is determined by two competing contributions: a positive Lorentz scattering and a negative s-d scattering. The atomic disorder in Co2CrAl films drastically changes MR behavior due to its strong influence on the magnetic properties.  相似文献   

18.
The real part R s and the imaginary part X s of the surface impedance Z s=R s+ iX s of Tl2Ba2CaCu2O8−δ and YBa2Cu3O6.95 single crystals have been measured with high precision at frequency ω/2π=9.4 GHz in the temperature range 0<T<140 K. In the Tl2Ba2CaCu2O8−δ crystal a linear temperature dependence R s(T) has been found for T⩽50 K, and the magnetic field penetration depth λ(4.2 K)=X s(4.2 K)/ω μ 0≈3760 Å has been measured. Along with well known features of the function Z s(T) in high-quality YBa2Cu3O6.95 single crystals, such as the linearity of λ(T) and R s(T) for T<T c/3 and a maximum of R s(T) at TT c/2, the linearity range of λ(T) extends to T≃50 K, and this curve has a plateau in the range 60<T<85 K. The curve of R s(T) in both the superconducting and normal states of YBa2Cu3O6.95 is well described by a two-fluid model with the electron-phonon mechanism of quasiparticle relaxation. A formula describing the curve of λ 2(0)/λ 2(T) throughout the studied temperature range is also given. Zh. éksp. Teor. Fiz. 112, 2210–2222 (December 1997)  相似文献   

19.
High temperature superconductors HoBa2Cu3O7−δ (T c ≅93 K), Ho0.5Y0.5Ba2Cu3O7−δ (T c ≅93 K) and ErBa2Cu3O7−δ (T c ≅95 K) were investigated by the zero-field μSR-technique. The muon spin depolarisation rate connected with the fluctuation frequency of rare-earth ion magnetic moments was measured. It was found that the samples with holmium show a fast increase of the muon spin depolarisation rate at temperatures below 20 K, while in ErBa2Cu3O7−δ the depolarisation rate remains low in the whole temperature region studied (4.2 K-270 K). The sharp difference between the behaviours of the muon spin depolarisation rate may be explained by the difference between the ground state of Ho3+ and Er3+ ions in the crystalline field of the lattice.  相似文献   

20.
In the temperature range of T = 150–400 K, the dependence of spectral widths (cm−1) on temperature, 182 + 0.38(±0.01)T and 217 + 0.48(±0.01)T, respectively, has been obtained for dimole emission of O2(a, 0) + O2(a, 0) → O2(X, 1) + O2(X, 0) + hν (λ = 703 nm) and O2(a, 0) + O2(a, 0) → O2(X, 0) + O2(X, 0) + hν (λ = 634 nm). It was shown that the ratio of dimole emission rate constants does not depend on temperature in the range of 150–400 K and is 1.06 ± 0.01.  相似文献   

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