Effects of high vacancy concentrations on the magnetic properties of La{sub 1{minus}x}Mn{sub 1{minus}y}O{sub 3} (0.02{le}x, y{le}0.13)
- Blackett Laboratory, Imperial College, London, SW7 2BZ (United Kingdom)
- Instituto de Ciencia de Materiales de Madrid, C. S. I. C, Cantoblanco, 28049 Madrid (Spain)
- Department of Materials, Imperial College, London, SW7 2BZ (United Kingdom)
It has been found that the synthesis conditions and subsequent annealing treatments can significantly change the magnetic and transport behavior of the colossal magnetoresistive materials of the general formula La{sub 1{minus}z}A{sub z}MnO{sub 3}, where A is a divalent ion. In order to clarify the role of vacancies within this structure, resistivity and magnetization measurements have been carried out on a series of samples derived from the parent compound LaMnO{sub 3}, with La and Mn vacancies introduced by systematically varying the oxygen annealing conditions. Previous studies have shown that for a given carrier concentration, the Curie temperature of the paramagnetic to ferromagnetic transition (T{sub c}) increases as the tolerance factor of the perovskite structure increases and then begins to decrease slowly for even higher tolerance factors. Generally, T{sub c} also increases with the Mn{sup 4+} content, consistent with a double exchange mechanism responsible for ferromagnetism. In this study T{sub c} was found to decrease as the vacancy concentration (and therefore the Mn{sup 4+} concentration) and tolerance factor both increase. The magnetic and transport data are discussed in the light of structural information obtained from neutron diffraction studies. In the present study it is found that La and Mn vacancies play a significant role in determining the physical properties of these materials: for high vacancy concentrations (x,y{ge}0.080) the magnetic properties are analogous to those of spin glasses associated with disorder and frustration. Semiconductorlike resistivity was observed for all samples at all temperatures. {copyright} {ital 1998 American Institute of Physics.}
- OSTI ID:
- 565619
- Journal Information:
- Journal of Applied Physics, Vol. 83, Issue 1; Other Information: PBD: Jan 1998
- Country of Publication:
- United States
- Language:
- English
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