| Autor: |
R Mahendiran, Tiwary, S. K., Raychaudhuri, A. K., Ramakrishnan, T. V., Mahesh, R., Rangavittal, N., Rao, C. N. R. |
| Jazyk: |
angličtina |
| Rok vydání: |
1996 |
| Předmět: |
|
| Zdroj: |
Scopus-Elsevier |
| ISSN: |
2381-3652 |
| Popis: |
Results of a detailed investigation of the structure and electron-transport properties of $La_{1-x}A_xMnO_3$ (A =Ca, Sr) over a wide range of compositions are presented along with those of parent $LaMnO_3$ containing different percentages of $Mn^{4+}$. The electrical resistivity $(\rho)$ and magnetoresistance (MR) of polycrystalline pellets have been measured in the 4.2–400 K range in magnetic fields up to 6 T and the Seebeck coefficient (S) from 100 to 400 K. The electrical measurements were supplemented by ac susceptibility and magnetization measurements. MR is large and negative over a substantial range of compositions and peaks around temperatures close to the ferromagnetic transition temperatures $(T_c)$. An insulator to metal-like transition occurs near the $T_c$ and the temperature dependence of $\rho$ below $T_c$ is related to the magnetization although $\rho$ in the metallic state is generally much larger than the Mott’s maximum metallic resistivity. The occurrence of giant magnetoresistance is linked to the presence of an optimal proportion of $Mn^{4+}$ ions and is found in the rhombohedral and the cubic structures where the Mn-O distance is less than 1.97 \AA and the Mn-O-Mn angle is $170^o\pm10^o$. The field dependence of MR shows the presence of two distinct regimes. The thermopower S shows a positive peak in the composition range at a temperature where MR also peaks; S becomes more negative with increase in $Mn^{4+}$. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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