Correlation length in La{sub 1{minus}x}Ca{sub x}MnO{sub 3} (abstract)
- Reactor Radiation Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)
- University of Maryland, College Park, Maryland 20742 (United States)
Small-angle neutron scattering (SANS) has been used to measure the ferromagnetic correlation length in La{sub 0.67}Ca{sub 0.33}MnO{sub 3}. This is of interest in these materials because the transport mechanism responsible for colossal magnetoresistivity involves valence fluctuation on the Mn sites, and thus, spin fluctuations. There should then be a direct relationship between the magnetoresistivity and the spin{endash}fluctuation correlation length. The magnetic SANS was determined by substracting 15 K data from the data at and above T{sub C} (250 K). When the quasistatic approximation is valid, the magnetic SANS measures the static equal-time two-spin correlation function. In an ideal isotropic ferromagnet, the fluctuations that drive the phase transition are the transverse (below T{sub C}) spin waves, which have a divergent correlation length at and below T{sub C}. Our measurements show that the magnetic scattering function for temperatures above T{sub C} is approximately Lorentzian. However, the extracted correlation length is anomalously small, starting at about 6 {Angstrom} at 400 K and increasing only to about 11 {Angstrom} at the nominal T{sub C}=250 K. The correlation length continues to increase below T{sub C} to about 14 {Angstrom} at 225 K. Inelastic scattering measurements suggest that there are significant diffusive fluctuations near T{sub C} in addition to the spin waves. We are performing SANS measurements in a magnetic field to try to separate the correlation lengths of these two types of fluctuations. {copyright} {ital 1997 American Institute of Physics.}
- OSTI ID:
- 496594
- Report Number(s):
- CONF-961141--
- Journal Information:
- Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 8 Vol. 81; ISSN JAPIAU; ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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