A. Chainani

Large magnetoresistance in La1−xSrxMnO3 and its dependence on magnetization

In this letter we report large magnetoresistance (MR) in ceramic samples of La1?xSrxMnO3 (0.1?x?0.4) in the temperature range 4.2 K?T?350 K in fields up to 6 T. We find that a large negative and isotopic MR exists for the whole composition range studied and the absolute value of resistivity change on application of magnetic field is more for samples with lower x which have higher resistivity. We find that the large MR occurs in the ferromagnetic state only and MR has a close relation with the magnetization M.

The large magnetoresistance of La1-xSrxCoO3 at low temperatures

We report here the resistivity ( rho ) and the magnetoresistance (MR) of the ferromagnetic perovskite oxide system La1-xSrxCoO3 (0.1 0.2) the magnitude of the MR is typically small (<10%), it is large in the composition range where x<or=0.2, where the system is close to the metal-to-insulator transition. We compare these observations with those made for the La1-xSrxMnO3 system.

Photoemission study of porous silicon

We report x‐ray photoelectron spectra from a porous silicon film (PSF) with a photoluminescence peak at 1.8 eV, as a function of argon ion etching time to probe the composition in the surface and the subsurface regions. The results clearly indicate that the surface layer is essentially a fluorine admixed SiO2 phase, while the Si:O:F composition of the subsurface region 2:1:0.2. With the possibility of the existence of hydrogen in this composition it appears that beyond the highly oxidized surface, PSF is a fluorine substituted siloxene derivative, which can be responsible for the visible photoluminescence.

Electronic Structure of and the Metal-Insulator Transition in La1-xSrxCoO3-δ: A Soft-X-Ray Absorption Study

We report the soft-X-ray absorption spectra at the oxygen K-edge of La1-xSrxCoO3-δ (x = 0.0, 0.1, 0.2, 0.3 and 0.4) series with experimentally determined δ values. We show that the doping of holes by replacing La3+ with Sr2+ induces states within the band gap of the insulating undoped compound for small x and these doped states have a very substantial oxygen 2p character. This indicates that the insulating compounds belong to the charge transfer insulator regime. With increasing Sr content, the doped states broaden into a band overlapping the top of the primarily oxygen p-derived band, leading to an insulator-metal transition at x ≥ 0.2.

Calculated oxygen 1s core-level photoemission spectra from cuprate superconductors

The observed O 1s X-ray photoemission spectra of the cuprate superconductors often exhibit a satellite at a higher binding energy to the main peak. The origin of this satellite is not fully understood. We have done model cluster calculations to investigate the origin of this satellite using the configuration interaction approach. The calculated spectra for the divalent and superconducting cuprates essentially exhibit a single peak. On distorting the cluster in-plane, the peak shifts to higher binding energies. This substantiates a deterioration of the surface leading to the observed satellite structure in the O 1s core-level photoemission spectra of the cuprate superconductors.

Electrical resistivity anomalies in the perovskites La1−xSrxMnO3

Abstract The temperature dependence of the resistivity of La 1−x Sr x MnO 3 indicates that the samples are semiconducting for x = 0.0 and 0.1, but metallic for x ⩾ 0.2 at lower temperatures. The metallic compositions exhibit broad maxima in the range 150–250 K and also a magnetic hysteresis at 300 K. Below 30 K, we see an increase in the resistivity for the metallic samples, the temperature dependence of which indicates the importance of electron-electron interactions in these systems.