Magnetoresistance of Very Pure Polycrystalline Aluminum

The behavior of the resistance of polycrystalline aluminum wires as a function of magnetic field and purity at temperatures of 4, 15, and 19.6 K is reported. Both longitudinal and transverse configurations were measured. The residual resistance ratios of the specimens varied from 1600 to 31 000. The measured magnetoresistance ($\frac{\Delta R}{R_0}$) is separated into a saturating and a linear part. The value of the saturating component is high at 19.6 K but is shown to be less than 6, even in the limit of infinite specimen purity. The linear component varies with both temperature and purity. Possible sources for the large saturating magnetoresistance values and for the variations observed in the linear portion are discussed. An analysis scheme is presented which allows prediction of the saturating component from zero-field resistance values. A deviation from Matthiessen's rule observed here, and by several other experimenters, is presented and discussed.