Ni-doped Compounds Research Articles

Synthesis, structure, oxygen stoichiometry, and electrical properties of doped ruddlesden-popper strontium cobaltite Sr1·875Ce0·025CoO4-δ, Sr1·875Ce0·025Co0·75Ni0·25O4+δ novel compounds

We report the synthesis of Sr1·875Ce0·025CoO4-δ and Sr1·875Ce0·025Co0·75Ni0·25O4+δ for the first time, each compound was synthesised using Co-precipitation and Sol-Gel methods, at 1050 °C for 144 and 120 h respectively. Oxygen stoichiometry was determined using Iodometric titration, we have noticed oxygen hypostoichiometry for Ce-doped compound and hyperstoichiometry state after Ni-doping. Electrical properties were studied for sintered pellets, Electrical resistance was measured in the range (−0.5–+0.5 v). Specific electrical resistivity and electrical conductivity were calculated from resistance measurements. It was found that the Ce-doped compound has about three times higher conductivity (σC1 = 0.000000058423295 s cm−1) Compared with the Ni-doped one (σN2 = 0.000000022384787 s cm−1). Electrical Capacitance was measured at 1 kHz frequency, the relative dielectric constant εr, and the loss tangent tanδ were calculated accordingly. The results showed that the Ni-doped compound has higher capacitance but lower εr and dissipation factor values.

Thermal conductivity of giant magnetocaloric Mn compounds

Temperature dependence of the thermal conductivity of Mn1.03As0.70Sb0.30 and Ru-doped or Ni-doped (MnFeRu)2(PSi) was studied. These compounds undergo a first-order magnetic transition (FOMT) near room temperature and exhibit a giant magnetocaloric effect at around the Curie temperature. The thermal conductivity of Ru-doped and Ni-doped compounds is abruptly reduced at the Curie temperature during the first cooling. This is due to the micro-cracks generated during the FOMT. On heating, the thermal conductivity shows positive temperature dependence. The Ru-doped and Ni-doped compounds show small humps in the temperature dependence of the thermal conductivity near TC. The thermal conductivity of ferromagnetic metals is given by the sum of the phonon component, the electronic component, and the magnetic component. The results are discussed by taking account of the temperature dependence of each component.

Crystal growth, electronic structure, and properties of Ni-substituted FeGa3

Crystals of the Fe1−xNixGa3 limited solid solution (x<0.045) have been grown from gallium flux. We have explored the electronic structure as well as magnetic and thermoelectric properties of Fe0.975Ni0.025Ga3 in comparison with Fe0.95Co0.05Ga3, following the rigid band approach and assuming that one Ni atom donates twice the number of electrons as one Co atom. However, important differences between the Co- and Ni-doped compounds are found below 620K, which is the temperature of the metal-to-insulator transition for both compounds. We have found that Fe0.975Ni0.025Ga3 displays lower degree of spatial inhomogeneity on the local level and exhibits diamagnetic behavior with a broad shallow minimum in the magnetic susceptibility near 35K, in sharp contrast with the Curie–Weiss paramagnetism of Fe0.95Co0.05Ga3. Transport measurements have shown the maximum of the thermoelectric figure-of-merit ZT of 0.09 and 0.14 at 620K for Fe0.975Ni0.025Ga3 and Fe0.95Co0.05Ga3, respectively.

Investigation of Mn, Fe, and Ni incorporation in CeCo2Al8.

Single crystals of CeCo(2-x)M(x)Al(8) (M = Mn, Fe, Ni; 0 ≤ x < 1) were grown and characterized by X-ray diffraction and magnetic susceptibility. The unit cell volumes of Mn-doped compounds increase and those of Ni-doped compounds decrease with increasing dopant concentration. All samples display a magnetic ordering near 6 K with magnetic moments of the analogues ranging from 2.61 to 2.81 μ(B)/mol Ce and slightly higher than Ce(3+) only magnetic moment. The unit cell volumes of Fe-doped compounds also increase with increasing Fe concentration. However, the cell volume of CeCo(2-x)Fe(x)Al(8) decreases for x = 1.00 and is not Curie-Weiss possibly because of valence fluctuation.

Incoherent effect of Fe and Ni substitutions in the ferromagnetic-insulator La0.6Bi0.4MnO3+δ

A comparative study of the effect of Fe and Ni doping on the bismuth based perovskite La0.6Bi0.4MnO3.1, a projected spintronics magnetic semiconductor has been carried out. The doped systems show an expressive change in magnetic ordering temperature. However, the shifts in ferromagnetic transition (TC) of these doped phases are in opposite direction with respect to the parent phase TC of 115 K. The Ni-doped phase shows an increase in TC ∼200 K, whereas the Fe-doped phase exhibits a downward shift to TC∼95 K. Moreover, the Fe-doped is hard-type whereas the Ni-doped compound is soft-type ferromagnet. It is observed that the materials are semiconducting in the ferromagnetic phase with activation energies of 77 &amp; 82 meV for Fe &amp; Ni-doped phases, respectively. In the presence of external magnetic field of 7 T, they exhibit minor changes in the resistivity behaviors and the maximum isothermal magnetoresistance is around −20% at 125 K for the Ni-phase. The results are explained on the basis of electronic phase separation and competing ferromagnetic and antiferromagnetic interactions between the various mixed valence cations.

High temperature ferromagnetism in Ni-doped In2O3 and indium-tin oxide

Observation of high temperature ferromagnetism in Ni-doped In2O3 and indium-tin-oxide (ITO) samples prepared by a solid state synthesis route is reported. Both Ni-doped compounds showed a clear ferromagnetism above 300K with the magnetic moments of 0.03–0.06μB∕Ni and 0.1μB∕Ni at 300 and 10K, respectively. Ni-doped In2O3 samples showed a typical semiconducting behavior with a room temperature resistivity of ρ∼2Ωcm, while Ni-doped ITO samples were metallic with ρ∼2×10−2Ωcm. Analysis of different conduction mechanisms suggested that variable range hopping model explains our ρ-T data for the Ni-doped In2O3 sample the best.

Phase separation and ferromagnetic transition inB-site substitutedNd1/2Ca1/2MnO3

$B$-site substitution effects on the structural and magnetic properties are investigated in ${\mathrm{Nd}}_{1/2}{\mathrm{Ca}}_{1/2}$$({\mathrm{Mn}}_{0.97}{M}_{0.03})$${\mathrm{O}}_{3}$ $(M=\mathrm{Al},$ Zn, Sc, Fe, Ni, Co, and Cr). With decreases of temperature below $\ensuremath{\sim}200 \mathrm{K},$ these compounds transform into a two-phase state. With further decrease of temperature below $\ensuremath{\sim}100 \mathrm{K},$ the Cr-, Co-, and Ni-doped compounds show the ferromagnetic transition, while the other compounds show only the antiferromagnetic component. We discuss these dopant-dependent ferromagnetic transition in terms of the effective one-electron bandwidth of the ${e}_{g}$ band.

The Gd ESR measurements in GdBa 2(Cu 1−xM x) 3O y (M= Ni, Co, and Fe) compounds

Electron-Spin-Resonance measurements are performed in GdBa2(Cu1−xMx)3Oy (M= Ni, Co, and Fe) compounds by using X, K, and Q-band measurements. The frequency dependence of the linewidths are observed. For GdBa2Cu3Oy compounds, the interactions among Gd ions are explained by the indirect exchange interaction of 6 kOe and the dipolar interaction of 3 kOe. In the Ni doped compounds, the linewidth broadening due to the decreasing of the exchange fields is observed. The same broadening is also observed in the Fe doped and quenched compounds. In this report, the magnetic behaviors of doped ions are discussed from the Gd ESR measurements.

Magnetic interactions of Gd in GdBa2(Cu1-xNix)3Oy compounds.

Electron-spin resonance (ESR) and dc-susceptibility are measured for ${\mathrm{GdBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{y}}$ compounds. From the Curie-Weiss susceptibility and the frequency dependence of the linewidth, we determine Gd dipolar fields of about 3 kOe and exchange fields of about 9 kOe in this system. In order to make the origin of the exchange fields clear, ESR measurements are also performed for Ni-doped compounds. The Gd linewidths and the N\'eel temperature depend on the Ni concentrations. The origin of the exchange field in ${\mathrm{GdBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{y}}$ compounds is discussed on the basis of the results obtained.