Kohler's Rule and the Transverse Magnetoresistance of Very DiluteCuMn,CuFe, andCuCo Alloys

The transverse magnetoresistance has been measured at 4.2 °K in polycrystalline alloys of Cu containing Co, Fe, or Mn, three solutes of respectively increasing magnetism. The solute concentrations are in the range 9-4000 at. ppm. Deviations from Kohler's rule in the low-field condition confirm the relative anisotropies of the solute potential scattering previously obtained from the Hall effect, and incidentally lead to a value of $\frac{{\tau }_B}{{\tau }_N}$ of 0.9 for Co in Cu. The dependence upon solute concentration of the negative magnetoresistance in the CuMn alloys (23-271 ppm) shows an unexplained property: It is concentration independent and in agreement with previous work for the more concentrated samples, but becomes dependent upon concentration below about 70 ppm where no previous measurements exist. The importance of sample size effects in such measurements upon very dilute alloys is illustrated.