Spin Diffusion in Double-Exchange Manganites

The theoretical study of spin diffusion in double-exchange magnets by means of dynamical mean-field theory is presented. We demonstrate that the spin-diffusion coefficient becomes independent of the Hund’s coupling $J_H$ in the range of parameters $J_{H}S\gg W\gg T$, $W$ being the bandwidth, relevant to colossal magnetoresistive manganites in the metallic part of their phase diagram. Our study reveals a close correspondence as well as some counterintuitive differences between the results on Bethe and hypercubic lattices. Our results are in accord with neutron-scattering data and with previous theoretical work for high temperatures.

Figure 1

Interacting DOS $N(\omega )$ for several values of $J_{H}S$ for the Bethe (solid lines) and hypercubic (dashed lines) lattices.

Figure 2

${\mathcal{D}}_s\chi z/a^2$ versus $n$ for several $J_{H}S$ for the Bethe (solid lines) and hypercubic (dashed lines) lattices.

Figure 3

${\mathcal{D}}_s\chi /a^2$ as a function of $x$. Experimental values of ${\mathcal{D}}_s$ are from Fig. 5 of Ref. 3, ${\chi }^{\mathrm{e}\mathrm{x}\mathrm{p}}$ is described in the text, theoretical results are from Eq. (9) for $J_{H}S\gg 1$.