Scaling Behavior of Anomalous Hall Effect and Longitudinal Nonlinear Response in High-Tc Superconductors

Based on existing theoretical model and by considering our longitudinal nonlinear response function, we derive a nonliear equation in which the mixed state Hall resistivity can be expressed as an analytical function of magnetic field, temperature and applied current. This equation enables one to compare quantitatively the experimental data with theoretical model. We also find some new scaling relations of the temperature and field dependency of Hall resistivity. The comparison between our theoretical curves and experimental data shows a fair agreement.Comment: 4 pages, 3 figure

Structural and magnetic properties of Cu substituted manganites studied by EXAFS and dc magnetization measurements

We report extended X-ray absorption fine structure (EXAFS) measurements at the Mn K-edge and dc magnetic measurements performed on (La1 12xCax)(Mn1 12yCuy)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\u2013Teller 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

Formation and mobility of oxygen vacancies in RuSr2GdCu2O8

Oxygen vacancies are introduced in the RuO2 and possibly CuO2 planes of RuSr2GdCu2O8 by annealing in vacuum above 600 K. The diffusive jumps of the O vacancies are accompanied by a reorientation of the local distortion, and are probed by measuring the elastic energy loss and modulus versus temperature at 1\u201310 kHz. An intense acoustic absorption peak develops near 670 K at 1 kHz and finally stabilizes after heating up to 920 K in vacuum. The analysis of the peak shows a barrier for the O diffusion of .1.4 eV, and a slowing down of Curie-Weiss type, with TC54002470 K, due to the interaction among the O vacancies. A secondary peak is attributed to O vacancies trapped at defects in the RuO2 planes, or to vacancies in the CuO2 planes. No sign of structural phase transformation is found up to 920 K

Effect of Cu2+ and Ni2+ substitution at the Mn site in (La0.63Ca0.37)MnO3: a neutron powder diffraction investigation

The crystal and magnetic structures of the (La0.63Ca0.37)(Mn1xTMx)O3 compounds (x = 0.00, 0.03,0.08; TM = Cu2+, Ni2+) were investigated between 5K and 300K by means of dc magnetic measurements and neutron powder diffraction analysis followed by Rietveld refinement. Both substituting cations lead to a reduction of the long range ferromagnetic ordering temperature; ferromagnetism is strongly suppressed in the 8% Cu-substituted sample, wherel ong- and short-range FM magnetic orders coexist together with short-range A-type AFM order. This particular feature can be related to the Jahn\u2013Teller character of Cu2+, absent in Ni2+, and suggests the occurrence of a quantum critical point in the (La0.63Ca0.37)(Mn1xCux)O3 system

Crystal and magnetic structure of Cr- and Ni-substituted (La0.50Ca0.50)MnO3

The crystal and magnetic structure of (La0.50Ca0.50)(Mn1 12xBx )O3 (x = 0.00, 0.03, 0.08; B = Cr, Ni) has been investigated between 5 and 300 K by means of dc magnetic measurements and neutron powder diffraction followed by Rietveld refinement. In the pristine compound an orthorhombic to monoclinic phase transition is detected on cooling, accompanied by a CE-type antiferromagnetic (AFM) ordering arising. Ni2+ and Cr3+ substitutions have similar effects on the structural and magnetic properties of (La0.50Ca0.50)MnO3, despite the fact that these ions are characterized by different external electronic configurations. After substitution, the orthorhombic to monoclinic phase transition is hindered. As a consequence, charge and orbital orderings are suppressed, as is the superexchange; double exchange takes place inducing ferromagnetic (FM) interactions. No evidence for stable magnetic interaction between Cr3+ or Ni2+ and the neighbouring Mn ions was detected. Nevertheless, in the Ni-substituted samples a detectable quantity of monoclinic phase forms during cooling, inside which AFM interactions take place. The amount of this secondary monoclinic phase decreases on increasing Ni substitution; the global FM magnetic moment decreases as well, due to a spin-cluster glass-type state arising. As a result a FM state is found to coexist with a spin-cluster glass-type state

A.C. susceptibility and magnetization of high-Tc superconductors: Critical state model for the intergranular region

A.C. susceptibility and magnetization measurements on a sintered YBa2Cu3O7 12y sample are presented. The measured magnetization is separated into two terms: one depending on the grains, the other on the intergranular region magnetization. For intergranular region we intend a desordered array of holes surrounded by a shell whose thickness is \u3bb at the surface of the grains connected through Josephson junctions. At these holes the fluxoids are pinned. In presence of a fluxoid gradient, a net macroscopic magnetization current results from the sum of all the microscopic components, as in the traditional type II superconductors. The contribution of the intergranular region to the magnetization is well explained in terms of the critical state model, if a critical current density strongly dependent on the magnetic field is assumed

Small angle neutron scattering study of magnetic clustering in (Pr0.55Ca0.45)(Mn1-yCry)O3 manganites

In the present paper we report a small angle neutron scattering (SANS) study of magnetic clusters formation in (Pr0.55Ca0.45)(Mn1yCry)O3 (y = 0.00, 0.03, 0.06) manganites which was performed by analyzing, above and below the magnetic phase transitions, the momentum transfer q dependence of the SANS intensity on temperature and on the applied magnetic field 0 < H < 5 T. Thermal scans between 5 and 300 K in zero field, 1 and 5 T as well as isothermal field-scans at three different temperatures were collected in the suitable q range on each sample. These measurements allowed us to determine the spatial dimensions, density and distribution of the non-overlapping ferromagnetic clusters before, during and after their formation, both in the insulating high temperature and in the percolating low temperature phases. Our results indicate that the magnetic clusters formation is favoured by Mn/Cr partial substitution, thus emphasizing the importance of magnetic polarons in the natural tendency of manganites to phase separation and the possibility to tune by chemical substitution the relative weight of one phase component with respect to the other one

Crystal and magnetic structure of Cr- and Ni-substituted (La0.50Ca0.50)MnO3

The crystal and magnetic structure of (La0.50Ca0.50)(Mn1 12xBx )O3 (x = 0.00, 0.03, 0.08; B = Cr, Ni) has been investigated between 5 and 300 K by means of dc magnetic measurements and neutron powder diffraction followed by Rietveld refinement. In the pristine compound an orthorhombic to monoclinic phase transition is detected on cooling, accompanied by a CE-type antiferromagnetic (AFM) ordering arising. Ni2+ and Cr3+ substitutions have similar effects on the structural and magnetic properties of (La0.50Ca0.50)MnO3, despite the fact that these ions are characterized by different external electronic configurations. After substitution, the orthorhombic to monoclinic phase transition is hindered. As a consequence, charge and orbital orderings are suppressed, as is the superexchange; double exchange takes place inducing ferromagnetic (FM) interactions. No evidence for stable magnetic interaction between Cr3+ or Ni2+ and the neighbouring Mn ions was detected. Nevertheless, in the Ni-substituted samples a detectable quantity of monoclinic phase forms during cooling, inside which AFM interactions take place. The amount of this secondary monoclinic phase decreases on increasing Ni substitution; the global FM magnetic moment decreases as well, due to a spin-cluster glass-type state arising. As a result a FM state is found to coexist with a spin-cluster glass-type state

Physical characterization of RuSr2GdCu2O8 sintered samples: An analysis of the magnetic measurements performed by a SQUID magnetometer

In this paper we present the resistive and magnetic characterization of sintered RuSr2GdCu2O8 samples. We show how the physical properties, related both to the superconducting and magnetic state, are affected by the final annealing step: one week in flowing oxygen. In doing so we perform a detailed analysis of the complexity of the dc magnetic measurements performed on such type of samples below the superconducting transition: in particular we discuss the structural and experimental reasons that make magnetic measurements in such a system so difficult. These reasons come from the simultaneous presence of two magnetic lattices and of the diamagnetism related to the superconducting state. The situation justifies, at least in part, the wide spread of results presented in the literature and the controversial visibility of the Meissner effect. We remark moreover the not negligible effect of the residual field and how it is possible to take it, at least in the zero field cooled magnetic procedure, into account