L.H. Zhao

Magnetization behavior of lightly doped La2CuO4+δ system

Abstract We have prepared a series of single-phase La 2 CuO 4δ samples by careful heat treatment in air. The sample magnetization measurements were performed from 4.2 K to 300 K. It was found that the magnetization behavior is strongly dependent on the annealing processing. With increasing annealing time and taking proper routes, the temperature dependence of the magnetization M ( T ) changes from a significant broad antiferromagnetic (AFM) transition around 250 K followed by a paramagnetic feature to a sharp AFM transition followed by a diamagnetic effect at 34 K. A possible explanation for this phenomenon with phase separation and superconductivity is presented.

The role of excess Cu on La2CuO4 system

The Cu-rich La2CuO4+delta ([La]:[Cu] = 2:1 + x) samples with 0 less than or equal to x less than or equal to 0.18 are characterized using X-ray diffraction, transmission electron microscopy and electron energy loss spectrum methods. The excess Cu is identified to occupy the La site and the maximum of such substitution, i.e., the maximum of excess Cu content, x, is examined to be about 0.06. From the magnetization measurements of the samples with different excess Cu, we find that the substitution of Cu for La can remarkably enhance the three-dimensional antiferromagnetic exchange interaction, thus, promoting electronic phase separation in La2CuO4+delta system with delta < 0.01

Observation of ferromagnetic correlation in phase-separated Cu-rich La2CuO4.003

Angle-resolved photoemission near the (K) over bar point in the surface Brillouin zone (SBZ) reveals the existence of a state 2.8 eV below the Fermi level which has the properties of an interface state. For Fe coverage Theta 0.5 mi, the feature gets stronger again and saturates at Theta = 1.0-1.3 ml. After subtracting the contribution from the surface state of clean Cu{1 1 1}, the feature grows in intensity with Theta increasing. For larger coverage (Theta > 3-4 ml), the intensity of the feature remains nearly constant relative to that of the bulk Cu features. Its binding energy is independent of the photoelectrom momentum perpendicular to the surface. The energy dispersion curve of the interface state lies in the gap of the projected bulk Cu band structure near the (K) over bar point. We conclude that the -2.8 eV feature comes from the interface between Fe overlayer and Cu{1 1 1} substrate

Magnetization investigation of phase separation in La2CuO4+δ system

Abstract Magnetization measurements were performed on Cu-, Sr-doped and undoped La 2 CuO 4+δ samples before and after electrochemical oxidation. Experimental results showed that different samples exhibited different behaviors at various phase separation stages. Possible explanation is presented.

Enhancement of phase separation in light Cu-doped La2CuO4+δ system: evidence from TEM and magnetization measurements

Abstract Cu-doped and undoped La2CuO4+δ samples prepared under the same conditions have been investigated. It is distinctly shown that phase separation only exists in Cu-doped one, in which a stripe structure was observed at room temperature. This leads to a suggestion as that Cu doping may promote phase separation and the stripe structure is directly related to the phase separation.

Phase separation induced ferromagnetic correlation in Cu-rich La2CuO4.003 sample

Abstract The magnetic properties have been examined following the phase separation process for Cu-rich La 2 CuO 4.003 sample. The ferromagnetic correlation, which is represented as magnetic hysteresis loop, was found for the first time to evolve with the progress of phase separation. It is suggested that the detected ferromagnetic correlation is the result of spin polarization embedded in the hole-rich region due to phase separation.

Phase Separation and Stripe-Like Modulation Observation in Cu-doped La2CuO4+δ System

Cu-doped La2CuO4+δ samples were prepared and characterized by various techniques. It was found that Cu-doped La2CuO4+δ is much easier to phase separate into antiferromagnetic and superconductive phase than the La2CuO4+δ one prepared under the same conditions. One kind of stripe-like modulation was observed on its ab-plane by RHTEM at room temperature. After annealing the samples under Ar gas, this stripe modulation disappeared, and the phase separation no longer exists as well. The antiferromagnetic transition temperature also changed dramatically during these processes. The origin of the stripe-like modulation and the mechanism of phase separation are discussed

Effect of sputtering atmosphere on superconductivity of La2−xSrxCu1−yO4 thin films

c-axis oriented La2-xSrxCu1-yO4 (x similar to 0.15) films were grown by de magnetron sputtering on Y-stabilized ZrO2, SrTiO3 and LaAlO3 substrates. It was found that the zero resistance temperature, T-c0, and the lattice parameters of the films are strongly dependent on the sputtering O-2:Ar gas ratios. A strong thickness dependence of T-c0 was also found in this kind of film, T-c0 of 22 K was obtained on similar to 2000 Angstrom thickness film grown on LaAlO3 substrate. The O-2:Ar ratios primarily modify the copper content, rather than the oxygen content of the films. The variation of the Cu content of the films strongly dominates the superconductivity of the films. Copyright (C) 1996 Published by Elsevier Science Ltd.