# Structure, electron-transport properties, and giant magnetoresistance of hole-doped $LaMnO_3$ systems

Mahendiran, R and Tiwary, SK and Raychaudhuri, AK and Ramakrishnan, TV and Mahesh, R and Rangavittal, N and Rao, CNR (1996) Structure, electron-transport properties, and giant magnetoresistance of hole-doped $LaMnO_3$ systems. In: Physical Review B, 53 (6). pp. 3348-3358.

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## Abstract

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 $Mn^{4+}$.

Item Type: Journal Article Copyright of this article belongs to The American Physical Society. Division of Chemical Sciences > Solid State & Structural Chemistry UnitDivision of Physical & Mathematical Sciences > Physics 06 Mar 2007 19 Sep 2010 04:33 http://eprints.iisc.ernet.in/id/eprint/9257