The effect of disorder and fluctuations on the magnetotransport of a double-exchange ferromagnet (abstract)
- Naval Research Laboratory, Washington, D. C. 20375 (United States)
The discovery of colossal magnetoresistance (CMR) in the doped perovskite manganites has reawakened interest in the double-exchange mechanism proposed to Zener. To account for the close relation between ferromagnetism and metallic transport in lanthanum manganites doped with divalent cation (Ca, Sr, Ba) Zener claimed that an electron could delocalize on lattice of spins and still conform to Hund{close_quote}s Rule if a ferromagnetic coupling between spins were mediated by that same electron. Thus, the onset of metallic behavior (delocalization) is intimately linked to ferromagnetic ordering of the spin lattice. Clearly, the double-exchange mechanism provides some necessary physics but is not sufficient in explaining the key mystery of the CMR materials: What causes the large peak in the resistivity vs. temperature and why is it removed by an applied magnetic field. The effect of disorder and fluctuations on the double-exchange mechanism may provide the answers. Several sources of disorder in these materials act to form a mobility edge via Anderson localization: intrinsic divalent/trivalent cation disorder, off-diagonal disorder caused by the spin lattice and oxygen vacancy disorder. A mean-field calculation reveals that below the Curie temperature those carriers aligned opposite to the magnetization experience a narrowing band as the temperature is reduced. Fermi glass behavior is induced in this minority carrier band by the Fermi level falling below the mobility edge. However, the mean-field result does not contain a peak in resistivity since the majority carrier band does not behave as a Fermi glass and effectively {open_quote}{open_quote}shorts out{close_quote}{close_quote} the more resistive minority conduction channel. The formation of the resistivity peak requires the inclusion of ferromagnetic fluctuations above the Curie temperature that tend to {open_quote}{open_quote}mix{close_quote}{close_quote} the two conduction channels. (Abstract Truncated)
- OSTI ID:
- 279994
- Report Number(s):
- CONF-951101--
- Journal Information:
- Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 8 Vol. 79; ISSN JAPIAU; ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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