1,721,050 research outputs found
Synthesis of ternary phases in the C-Mg-Ni system by combustion
No full textBy applying the combustion synthesis technique on stoichiometric elemental powder compacts and subsequent suitable isothermal annealing treatements, the following three crystalline compounds were prepared: MgxCyNi3, MgNi2(C), Mg2Ni(C). The samples were analyzed by means of X-ray and synchrotron powder diffraction and scanning electron microscopy, coupled with electronic microprobe analyses. Their electric and magnetic properties were investigated between 1.5 and 300 K
Structural and magnetic properties of Cu substituted manganites studied by EXAFS and dc magnetization measurements
No full textWe report extended X-ray absorption fine structure (EXAFS) measurements at the Mn K-edge and dc
magnetic measurements performed on (La1−xCax)(Mn1−yCuy)O3 samples (x = 0.37 and 0.75 and y = 0.03
or 0.08), thus comparing the effects determined by the partial Mn substitution with Jahn–Teller Cu2+ ions
with those induced by the already studied analogous substitution of Mn with non-Jahn-Teller Cr3+.
Hence, in the present paper we complete our study on the influence of chemical Mn site substitutions
on the nanoscale phase inhomogeneity characteristic of these strongly correlated electron systems.
We observe that the Cu2+ substitution determines two very different effects in the two compositions
belonging from the opposite sides of the phase diagram. In the x = 0.37 case itweakens the ferromagnetic
ordering thus favouring the antiferromagnetic charge ordered phase component, while in the x = 0.75 one
it does not significantly modify the charge ordering already present in the system, differently from what
previously observed in presence of non-Jahn-Teller Cr3+ substitution
Magnetic characterization of sintered MgB2 samples: effect of substitution or 'doping' with Li, Al and Si
No full text
Thermoelectric and thermomagnetic effects in the mixed state analysis of the thermal angle
No full textIn this paper thermoelectric and thermomagnetic coefficients in the mixed state are discussed. Besides the contribution of the Abrikosov vortices, also the role of the vortex-antivortex pairs and of the quasi-particles unbounded and localized in the vortex core is considered. The vortex-antivortex contribution to the Seebeck and Nernst effects is calculated in detail. To study the role of normal excitation we propose to measure the thermal angle, alpha(th) that represents the direction of the vortex velocity. In fact, taking the unbounded quasiparticles into account, or not, as the temperature varies, alpha(th) shows an important difference in behavior, easy to detect experimentally. Measurements of the Seebeck effect and Nernst effect on a Bi(2223) tape are presented and the thermal-angle behavior is discussed. The experimental data are in agreement with the models that consider the unbounded quasiparticles contribution, but some caution must be taken as to the role of the Josephson vortices
Supercurrent lengthscale in sintered YBCO and critical state model.
No full textMagnetization measurements on sintered YBa2Cu3O7−y in two geometries (slab and cylinder) show the coexistence of two transport mechanisms: intergranular and intragranular currents. Both mechanisms can be explained in the framework of the critical state model. Using a simple law for the critical current versus magnetic field dependence, it is possible to calculate the magnetization and the in-phase and out-of-phase AC susceptibility and the agreement with the experimental data is good. Magnetization measurements on tubular samples have been performed too; these measurements, together with χAC measurements allow to determine the dimensions of magnetized regions
Neutron powder diffraction investigation on the crystal and magnetic structure of (Ho0.50+xCa0.50-x)(Mn1-xCrx)O3
No full textThe crystal and magnetic structure of (Ho0.50+xCa0.50-x)(Mn1-xCrx)O3 (x = 0:00, 0.01, 0.02, 0.03) has been investigated between 5 and 300 K by means of neutron powder diffraction followed by Rietveld refinement and dc magnetic measurements. During cooling an orthorhombic to monoclinic phase transition occurs on account of the charge and orbital ordering taking place in the Mn sub-lattice; at low temperature phase separation takes place
and the main monoclinic phase coexists with a secondary orthorhombic phase, whose amount slightly increases with the increase of Cr content. Cr3C is not involved in orbital ordering or superexchange interactions. The charge and magnetic ordering are decoupled: the Mn moments order according to a CE-type structure in all samples
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