Increasing Ni Doping Research Articles

Effect of nickel doping concentration on structural and magnetic properties of ultrafine diluted magnetic semiconductor ZnO nanoparticles

The ZnO:Ni 2+ nanoparticles of mean size 2–12 nm were synthesized at room temperature by the simple co-precipitation method. The crystallite structure, morphology and size were determined by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The wurtzite structure of ZnO gradually degrades with the increasing Ni doping concentration and an additional NiO-associated diffraction peak was observed above 15% of Ni 2+ doping. The change in magnetic behavior of the nanoparticles of ZnO with varying Ni 2+ doping concentration was investigated using a vibrating sample magnetometer (VSM). Initially, these nanoparticles showed strong ferromagnetic behavior, however, at higher doping percentage of Ni 2+, the ferromagnetic behavior was suppressed and paramagnetic nature was observed. The enhanced antiferromagnetic interaction between neighboring Ni–Ni ions suppressed the ferromagnetism at higher doping concentrations of Ni 2+.

Fluctuation-induced conductivity of polycrystalline Ni doped Cu0.5Tl0.5Ba2Ca2Cu3−yNiyO10−δ (y=, 0.5, 1.0, 1.5) superconductors

The fluctuation-induced conductivity of Ni free and Ni doped Cu0.5Tl0.5Ba2Ca2Cu3−yNiyO10−δ (y=0, 0.5, 1.0, 1.5) samples is investigated for comparison of dimensionality of fluctuations above the mean-field critical temperature. The temperature dependence of paraconductivity can be described by a power law following Aslamazov–Larkin (AL) type equations for these polycrystalline superconductors. It is observed from these studies that at higher temperatures, the fluctuations in the order parameter of the carriers follow two-dimensional (2D) AL behavior, whereas at lower temperatures (closer to transition temperature) their behavior is three-dimensional (3D) AL. From the analysis of our results, we have also evaluated the exponents of dimensionality, the coherence lengths, and the crossover temperatures. The crossover temperature from 2D to 3D have substantially been shifted to lower temperatures with increasing Ni doping, which is most likely related to the scattering of the carriers by remnant spins of Ni atoms. These scattering promote a reduction in the coherence length of the carriers along c-axis. These studies have also shown that the carrier concentration in the conducting CuO2 planes is the most essential; the role of antiferromagnetism in the mechanism of superconductivity is secondary.

Electrical transport and 1/f noise properties of LaFe1−xNixO3 (x = 0.3, 0.4 and 0.5) thin films

The electrical transport and 1/f conduction noise properties of LaFe1−xNixO3 (x = 0.3, 0.4 and 0.5) thin films have been studied. The temperature dependent resistivity data have been fitted with Mott's variable-range hopping model. From the resistivity data we have estimated various parameters, namely, the hopping distance (Rh), the hopping energy (Eh) and the density of states at the Fermi level (N(EF)). The decrease in the hopping energy and the increase in the density of states at room temperature have been observed with the increase in Ni doping for all samples. The Ni doping increases the density of charge carriers and enhances delocalization induced phenomena in the system. The magnitude of the normalized noise SV/V2 increases with the decrease in the Ni concentration over the whole temperature range. The conduction noise is also proportional to the square of the bias current, which confirms that the noise arises from the conduction fluctuations. The Hooge parameter (γ) calculated at room temperature is compared with its value in semiconductors and manganite/oxide materials. The observed features have been explained on the basis of charge-carrier doping in LaFeO3. The noise measurements in conjugation with the electrical properties of the film propose the propitious characteristic of the system.

Effects of Ni doping on B-site ordering and magnetic behaviors of double perovskite Sr2FeMoO6

Sr2FeMoO6 of double perovskite structure has attracted much attention recently, owing to its substantial low-field magnetoresistance reported at room temperature. In our study, a mechanical activation process is devised for successful formation of Ni-doped double perovskite Sr2(Fe1 − xNix)MoO6 (0.00 ≤ x ≤ 0.20). For the first time, a single phase of double perovskite is synthesized in air by using MoO2 as the starting material. Ni doping in Sr2FeMoO6 significantly affects its long-range B-site ordering and magnetic behaviors, where the B-site long-range order parameter is progressively enhanced with increasing Ni doping level. Both magnetization and the Curie temperature in Sr2FeMoO6 are enhanced significantly by Ni doping, where they both depend almost linearly on the degree of B-site long-range ordering.

산소 결핍된 TiO2-δ:Ni 박박의 자기적 성질 연구

We studied the magnetic and the related electronic properties of Ni-doped rutile films (including oxygen deficiency ) prepared using a sol-gel method. A room-temperature ferromagnetism was observed in the : Ni films with the saturation magnetization () decreasing with increasing Ni doping and remaining constant above 6 at% Ni doping. The observed ferromagnetism below 6 at% Ni doping is interpreted as due to magnetic polaron formed by a trapped electron in oxygen vacancy and magnetic impurity ions around it. For small Ni doping, up to was obtained. The ferromagnetism for Ni doping above 6 at% is interpreted as due to the existence of Ni clusters that can explain the p-n conductivity transition observed by Hall effect measurements.

Effect of Ni doping in rare-earth manganite La 0.7Pb 0.3Mn 1−xNi xO 3 ( [formula omitted

With Ni doping, La 0.7Pb 0.3Mn 1− x Ni x O 3 ( x = 0 – 0.5 ) system exhibits decrease of conductivity and increase of metal–insulator transition temperature. This is considered to occur because of the decrease of effective double exchange (DE) interaction due to Ni doping. The presence of majority of Ni 2+ states as indicated by the XPS study, govern the transport and magnetic properties of this system. The spin-wave stiffness constant D, characterising the magnon in the low-temperature ( T<T p) ferromagnetic phase, estimated from the magnetisation ( M) data, decreases with increasing Ni content. Unlike spin-glass-like pure insulating state below the Curie Temperature ( T C ), observed in other similar transition metal ion-doped systems, magnetisation (both zero field cooled (ZFC) and field cooled (FC) measured down to 10 K) and resistivity data of the samples indicate the existence of ferromagnetic cluster-like-state, which becomes more vivid with increasing Ni doping. Like many other colossal magnetoresistive (CMR) systems, small polaron hopping conduction is observed in the high-temperature ( T > T p ) semiconducting phase showing increase of activation energy as conductivity decreases.

Influence of electron-phonon interaction on the lattice thermal conductivity ofCo1−xNixSb3

We have investigated the effect of electron-phonon scattering in a series of n-type nickel-doped ${\mathrm{CoSb}}_{3}$ skutterudite materials. Samples were polycrystalline of the form ${\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}{\mathrm{Sb}}_{3}$ with $x=0,$ 0.001, 0.003, 0.005, 0.0075, and 0.01. The lattice thermal conductivity decreases dramatically with increasing Ni doping for $xl~0.003.$ For higher Ni concentration the reduction of the lattice thermal conductivity saturates. Our theoretical analysis indicates that this reduction of the lattice thermal conductivity cannot be explained solely by point-defect scattering of the phonons. Rather, we can fit the lattice thermal conductivity of Ni-doped ${\mathrm{CoSb}}_{3}$ by introducing an electron-phonon scattering mechanism, and this demonstrates that the electron-phonon interaction can play an important role in the reduction of the heat conduction in n-type skutterudites.