Perovskite manganites, which have the the general formula R1-xAxMnO3 (R = La, Pr, or Nd and A = Ca, Sr, Ba, or Pb), have generated much recent interest because they exhibit “colossal magnetoresistance” (CMR), i.e. a small change in an applied magnetic field dramatically changes the electrical resistance of the material. Materials that exhibit this effect are being developed for various field-sensing applications but currently, the mechanism by which CMR occurs is not known. Conduction in these materials is explained by the “double exchange” mechanism, where the conductivity is attributed to electrons hopping back and forth between neighboring manganes ions. Such hopping is a maximum when the magnetic moments of the magnese ions are aligned parallel and a minimum when they are aligned antiparallel. In short, these materials show metallic conductivity when they are ferromagnetic and insulating behavior when they are antiferromagnetic. Moreover, they change from metallic to insulating behavior as a function of temperature.