Electrical properties of Na-doped (SN)x single crystal

Electrical resistivity of (SN)_x crystal along the b-axis increases in Na ion solution by several times in a few tens of minutes. Temperature dependence of resistivity and transverse magnetoresistance at 4.2 K in Na-doped (SN)_x do not change remarkably from the pristine (SN)_x. These experimental results are discussed in terms of electron transfer from the dopant (Na) to (SN)_x into consideration, comparing with the case of halogen doping.     

Hall effect and magnetoresistance of (SN)x films

Hall effect and electrical conductivity have been investigated between 77 K and 300 K and the magnetoresistance at 4.2 K for a number of (SN)_x films deposited at substrate temperatures between — 10 and 50°C. The small magnitude of the Hall mobility (? 1 cm² Vsec^?1 at 300 K) and its activated temperature dependence are interpreted in terms of a heterogenous model for (SN)_x films with thin depletion layers separating highly conductive islands. The hole concentration in these islands (p ≈ 10²¹ cm^?3, the microscopic mobility (μ ≈ 500 cm² Vsec^?1 at 4.2 K) and the temperatures dependence of μ are found to be close to values for (SN)_x crystals.     

Temperature dependences of electrical resistivity and magnetic susceptibility in (SN)x single crystal

Pauli-paramagnetism is observed in high quality (SN)x single crystal. Density of state at Fermi level is estimated to be 0.14 ± 0.06 states/(eV spin molecule) from the observed magnetic susceptibility. Curie Weiss like laws are observed in γ-ray irradiated and low quality (SN)x crystals which show the resistivity minimum at 30–40 K. The resistivity minimum is discussed in terms of carrier scattering by localized paramagnetic centers.     

Optical correlation of functions distorted as f(x′)=>f(xa)

The use of coordinate transformation preprocessing is used to produce a space-variant correlator invariant to functions distorted as f(x′)=f(x^a). Such distortions arise in non-linear scanning devices, imaging from curved surfaces, aberrations in an imaging system, and in the Doppler shift of target with non-uniform motion.     

Exchange bias in structure-phase separated K0.8Fe2−xNixSe2 (x=0.015) single crystal: Interface evidence

Exchange bias behavior is observed in Ni slightly doped K_0.8Fe_2−xNi_xSe₂ (x=0.015) single crystal. Two distinguished phases with epitaxial growth were observed in X-ray diffraction experiments, indicating the structure phase separation in our samples. The magnetic hysteresis loop shifts in both horizontal and vertical directions when the sample was cooled down to 3 K in a magnetic field. The nature of this magnetic anisotropy could be understood as a result of the freezing properties of the local spin disorders in cluster like spin-glass system. Our results suggest that the sample contains short range weak ferromagnetic clusters (phase 2) embedding in the antiferromagnetic backgrounds (phase 1), in which the random distribution of Ni on Fe or Fe-vacancy sites quenched the superconductivity and induced spin disorders.     

Negative c-axis magnetoresistance in graphite

We have studied the c-axis interlayer magnetoresistance (ILMR), Rc(B) in graphite. The measurements have been performed on strongly anisotropic highly oriented pyrolytic graphite (HOPG) and single crystalline Kish graphite samples in magnetic field up to B=9 T, and the temperature interval 2 K?T?300 K. We have observed negative magnetoresistance, dRc/dB<0, for B‖c-axis for both samples above a certain field Bm(T)>5.4 T and 0.2 T for HOPG and Kish graphite, respectively. The results can be understood consistently by assuming that ILMR is related to a tunneling between zero-energy Landau levels of quasi-two-dimensional Dirac fermions, in a close analogy with the behavior reported for α-(BEDT-TTF)₂I₃ [N. Tajima, et al., Phys. Rev. Lett. 102 (2009) 176403], another multilayer Dirac electron system.     

Charge order melting and magnetic transition in Nd0.5(1+x)Ca0.5(1−x)Mn(1−x)CrxO3 system

The magnetic property of double doped manganite Nd_0.5(1+x)Ca_0.5(1−x)Mn_(1−x)Cr_xO₃ with a fixed ratio of Mn³⁺:Mn⁴⁺=1:1 has been investigated. For the undoped sample, it undergoes one transition from charge disordering to charge ordering (CO) associated with paramagnetic (PM)-antiferromagnetic (AFM) phase transition at T<250 K. The long range AFM ordering seems to form at 35 K, rather than previously reported 150 K. At low temperature, an asymmetrical M-H hysteresis loop occurs due to weak AFM coupling. For the doped samples, the substitution of Cr³⁺ for Mn³⁺ ions causes the increase of magnetization and the rise of T_c. As the Cr³⁺ concentration increases, the CO domain gradually becomes smaller and the CO melting process emerges. At low temperature, the FM superexchange interaction between Mn³⁺ and Cr³⁺ ions causes a magnetic upturn, namely, the second FM phase transition.     

Magnetism, magnetocaloric effect and positive magnetoresistance in Fe-doped antipervoskite compounds SnCMn3−xFex (x=0.05-0.20)

The effects of Fe substitution on the structure, magnetic properties, magnetocaloric effect and positive magnetoresistance (MR) effect in antipervoskite compounds SnCMn_3−xFe_x (x=0.05-0.20) have been investigated systematically. Partial substitution of Fe for Mn leads to the monotonic reduction in both the Curie temperature T_C and saturated magnetization (M_S). It can be attributed to the reduction of electronic density of state at the Fermi energy by Fe-doping. The maximum values of magnetic entropy change (−ΔS_M) and positive MR gradually decrease as x increases, due to the broadening of magnetic phase transition. The refrigerant capacity increases initially with x≤0.05, then decreases gradually as x increases further, which is suggested to originate from the competition between the decreasing −ΔS_M and broadening temperature span. Our result indicates that the chemical doping on Mn site is an effective method for manipulating the properties of antiperovskite compounds AXMn₃.     

Temperature dependence of the magnetoresistance of single crystal aluminium

The magnetoresistance of single crystal aluminium was measured with the magnetic field in the three main crystallographic directions [100], [110] and [111], in the temperature range 4.2–20 K and in magnetic fields up to 7 T. The exponent of a Tⁿ-law is shown to be decreasing with increasing fields.     

Feeding times in (HI, xnγ) reactions

Feeding times, T_f, for population of the quasi-rotational bands in a number of doubly even nuclei formed in (dHI, xn) reactions have been measured with the recoil-distance Doppler-shift technique. Values of 11±3, 5±2.5, 3±3 and 12_?4^+2.5 ps were obtained for T_f the ^{166, 168, 170}Hf and ¹⁷⁸Os nuclei populated by the ^150,152,154Sm(²⁰Ne,4n) and ¹⁵⁴Sm(²⁸Si,4n) reactions, respectively. In all cases the fraction of slow-feeding component was less than a few percent.     

Hot electron drift velocity in Hg1−xCdxTe (x=0.205)

Hot electron drift velocity in Hg_1?xCd_xTe (x=0.205) at 77 K is calculated by the Monte Carlo technique. Band nonparabolicity, admixture of wave functions, and two-mode nature of the polar optic phonons are included in addition to the effects of deformation potential acoustic, alloy and ionized impurity scattering. Good agreement with the experimental data is achieved.     

Room temperature magnetic entropy change and magnetoresistance in La0.70(Ca0.30−xSrx)MnO3:Ag 10% (x=0.0−0.10)

The magnetic and magnetocaloric properties of polycrystalline La_0.70(Ca_0.30−xSr_x)MnO₃:Ag 10% manganite have been investigated. All compositions are crystallized in single phase orthorhombic Pbnm space group. Both, the insulator–metal transition temperature (T^IM) and Curie temperature (T_c) are observed at 298 K for x=0.10 composition. Though both T^IM and T_c are nearly unchanged with Ag addition, the MR is increased. The MR at 300 K is found to be as large as 31% with magnetic field change of 1 T, whereas it reaches up to 49% at magnetic field of 3 T for the La_0.70Ca_0.20Sr_0.10MnO₃:Ag_0.10 sample. The maximum entropy change (ΔS_Mmax) at near its T_c (300.5 K) is 7.6 J kg⁻¹ K⁻¹ upon the magnetic field change of 5 T. The La_0.70Ca_0.20Sr_0.10MnO₃:Ag_0.10 sample having good MR (31%^1 T, 49%^3 T) and reasonable change in magnetic entropy (7.6 J kg⁻¹.K⁻¹, 5 T) at 300 K can be a potential magnetic refrigerant material at ambient temperatures.     

Phase transition in V1+xTe2 (0.04⩽x⩽0.11)

1T-V_1+xTe₂ was synthesized in a composition range of 0.04?x?0.11. The reversible first order transition was observed by DTA (DSC), powder X-ray diffraction, magnetic susceptibility (χ), and d.c. electrical resistivity (?) measurements. Transition temperature (T_t is 474 K for V_1.04Te₂, and decreases with increasing x. Heat of transition, ΔH was estimated to be as high as 500 cal mol^?1 from the endothermical peak in DSC. The expansion of the c-axis is observed at T_t. χ exhibits a jump at T_t, showing the paramagnetic temperature dependence both below and above T_t. ? measurements show the metallic-like behavior with a slight decrease at T_t. Preliminary electron diffraction examination suggests the formation of a super-structure below T_t.     

The scattering effects of the redistribution function RIII(x′, n′; x, n) on spectral line formation

The effects of frequency and angular redistribution on line formation are examined in static isothermal atmospheres for scattering described by the redistribution function R_III(x′, n′; x, n). For an optically thin atmosphere, it is found that the emergent line intensities obtained using R_III are essentially the same as R_I and R_II. In the case of a semi-infinite atmosphere, the emergent line intensities obtained using R_III, whether angle-averaged or angle-dependent, did not differ substantially from the complete redistribution results.     

Properties of the solid solution (1−x)Na0.5Bi0.5TiO3-(x)BiFeO3

This study shows that remarkable electric and magnetic properties are encountered within the (1−x)Na_0.5Bi_0.5TiO₃ (NBT)-(x)BiFeO₃ (BF) solid solution. Dual ferroelectric and magnetic properties are observed in the BF-rich part of the solid solution implying intrinsic multiferroic character of the compounds. In addition, a relaxation phenomenon is evidenced within the overall compositional domain of the solid solution. This study emphasizes that in the NBT-rich part, the relaxor behaviour is very similar to that of NBT, while beyond x=0.5, it turns to a different mechanism of relaxation probably induced by the presence of oxygen vacancies resulting from the mixed valence of the iron cations.     

The inverse problem for the third order equation uxxx + q(x)ux + r(x)u = −iζ3u

The spectral problem u_xxx + q(x)u_x + r(x)u = ?iξ³u is considered. A set of spectral data which is sufficient for the reconstruction of the potentials q(x) and r(x) is found and the problem of this reconstruction, this inverse problem solved.     

Polarization memory of luminescence from photo-generated carriers in aSixC1−x:H (x∼0.2)

Photoluminescence of aSi_xC_1?x:H (x～0.2) is studied with a particular interest on the localization of carriers. Taking the polarization memory of luminescence as a probe, we clarify the localized character of photo-generated carriers as functions of excitation photon energy, emitted photon energy, temperature and time. The picosecond time-resolved measurement of the polarization memory is shown useful to study dynamical relaxation processes of carriers in disordered systems.     

Low-field transport properties of (1−x)La0.7Ca0.2 Sr0.1MnO3+x(ZnO) composites

Composite samples (1−x)La_0.7Ca_0.2Sr_0.1MnO₃(LCSMO)+x(ZnO) with different ZnO doping levels x have been investigated systematically. The structure and morphology of the composites have been studied by the X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The XRD and SEM results indicate that no reaction occurs between LCSMO and ZnO grains, and that ZnO segregates mostly at the grain boundaries of LCSMO. The magnetic properties reveal that the ferromagnetic order of LCSMO is weakened by addition of ZnO. The results also show that ZnO has a direct effect on the resistance of LCSMO/ZnO composites, especially on the low-temperature resistance. With increase of the ZnO doping level, T_P shifts to a lower temperature and the resistance increases. It is interesting to note that an enhanced magnetoresisitance (MR) effect for the composites is found over a wide temperature range from low temperature to room temperature in an applied magnetic field of 3 kOe. The maximum MR appears at x=0.1. The low field magnetoresistance (LFMR) results from spin-polarized tunneling. However, around room temperature, the enhanced MR of the composites is caused by magnetic disorder.     

Electromagnetic properties of low-temperature co-fired xPZT+(1−x)NiCuZn-ferrite composites

To adjust the dielectric constant and the initial permeability of NiCuZn-ferrite materials for suppressing electromagnetic interference, Pb_0.95Sr_0.05(Zr_0.52Ti_0.48)O₃ (PZT) was introduced. The effects of PZT additive on the phase composition, densification, microstructures and electromagnetic properties of the ceramics with composition of xPZT+(1−x)NiCuZn-ferrite (where x=0-25 wt%) were investigated. The results show that these composites are mainly of spinel phase, exhibiting relatively high dielectric constant and initial permeability due to the mutual effects of magnetization of NiCuZn-ferrite phase and polarization of PZT phase. Meanwhile, relatively high-quality factor (Q) and excellent frequency stability were obtained for the samples with PZT additive. These materials are expected to be used as embedded inductors or embedded capacitors.