Chemical disorder and charge transport in ferromagnetic manganites

Disorder broadening due to randomly distributed ${\mathrm{La}}^{3+}$ and ${\mathrm{A}}^{2+}$ (A=Ca,Sr,Ba) cations is combined with a virtual-crystal treatment of the average system to evaluate the effects on both majority and minority transport in the ferromagnetic ${\mathrm{La}}_{2\mathrm{/}3}$ ${\mathrm{A}}_{1\mathrm{/}3}$ ${\mathrm{MnO}}_3$ system. The low-density minority carriers which lie in the band tail are localized by disorder, while the majority carriers retain long mean free paths reflected in the observed strongly metallic conductivity. In addition to obtaining transport parameters, we provide evidence that local distortions are due to nearby ionic charges rather than to ion size considerations.