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Unconventional Ferromagnetic Transition in La1-xCaxMnO3

J. W. Lynn, R. W. Erwin, J. A. Borchers, Q. Huang, A. Santoro, J-L. Peng, Z. Y. Li

cond-matarXiv:cond-mat/9604170

Abstract

Neutron scattering has been used to study the magnetic correlations and long wavelength spin dynamics of La1-xCaxMnO3 in the ferromagnetic regime (0<=x<1/2). For x=1/3 (Tc=250K) where the magnetoresistance effects are largest the system behaves as an ideal isotropic ferromagnet at low T, with a gapless (<0.04meV) dispersion relation E=Dq2 and D(T=0)~170 meV-A-1. However, an anomalous strongly-field-dependent diffusive component develops above ~200K and dominates the fluctuation spectrum as T approaches Tc. This component is not present at lower x.

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