Magnetoresistance anisotropy and field dependence have been studied in single crystals of iron and cobalt in fields up to 150 kOe in the temperature range 1-4.2 K. The crystals of iron and cobalt had residual resistance ratios up to ∼4600 and ∼400, respectively. The relation Δρρ0=aBn has been studied for both metals and in the case of iron the exponent n approaches values in the range 1.8-1.9 for fields up to 90 kOe and then decreases to the range 1.3-1.5 at 150 kOe. This decrease in the exponent has been observed for all field and current directions measured suggesting that extensive magnetic breakdown may occur. A preliminary measurement on iron to 215 kOe shows n decreasing to less than 1 for some field directions. Cobalt shows saturation behavior for most field and current directions but values of n>1 are observed for certain specific directions. The magnetoresistance rotation curves for iron exhibit sharp minima consistent with narrow bands of open orbits in the < 100 > and < 110 > directions. Minima are also observed which indicate open orbits in the < 310 >, < 410 >, and < 530 > directions. The behavior of cobalt suggests open orbits parallel to the basal plane and possibly along the c axis. Both metals show Shubnikov-de Haas oscillations which appear to be related to small pockets of the Fermi surface corresponding to 10-3-10-4 electrons per atom. In iron oscillations with frequencies in the range 1-6.2 MG have been observed while in cobalt three oscillations with frequencies of 1.07, 3.57, and 11.63 MG have been observed. The low-frequency oscillation in cobalt has been studied as a function of angle and indicates that two distinct branches exist as the field is rotated away from the c axis. Oscillations are observed on only one branch at a time and the behavior suggests the possible presence of magnetic breakdown. The data on both iron and cobalt have been compared to models of the Fermi-surface topology in these metals.
ASJC Scopus subject areas
- Condensed Matter Physics