Spin Dynamics of the Magnetoresistive Pyrochlore Tl_2Mn_2O_7

Abstract

Neutron scattering has been used to study the magnetic order and spin dynamics of the colossal magnetoresistive pyrochlore Tl_2Mn_2O_7. On cooling from the paramagnetic state, magnetic correlations develop and appear to diverge at T_C (123 K). In the ferromagnetic phase well defined spin waves are observed, with a gapless ($\Delta <0.04$ meV) dispersion relation E=Dq^{2} as expected for an ideal isotropic ferromagnet. As T approaches T_C from low T, the spin waves renormalize, but no significant central diffusive component to the fluctuation spectrum is observed in stark contrast to the La${}_{1-x}$(Ca,Ba,Sr)${}_x$MnO${}_3$ system. These results argue strongly that the mechanism responsible for the magnetoresistive effect has a different origin in these two classes of materials.

4 pages (RevTex), 4 figures (encapsulated postscript), to be published in Phys. Rev. Lett

References in corpus (1)

• Softening and Broadening of the Zone Boundary Magnons in Pr0.63Sr0.37MnO3

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