Magnetotransport and the Fermi surface of iron

Abstract

Transverse magnetoresistance oscillations have been measured in applied fields up to 220 kOe using both dc techniques and ac modulation techniques with second-harmonic detection. Single crystals of iron with residual resistance ratios of 3000 to 10 000 have been measured in the temperature range 1.1 to 4.2 K. Frequencies in the range 0.9 to 50 MG have been detected and compared to previous de Haas—van Alphen (dHvA) results. New frequencies are observed which were not present in dHvA results and these are interpreted as arising from interference areas fed by open-orbit networks. Prominent frequencies at 0.9 and 11.2 MG for $\overrightarrow{\mathrm{B}}\parallel \mathrm{}\left[001\right]\mathrm{}$ and at 0.97 MG for $\overrightarrow{\mathrm{B}}\parallel \mathrm{}\left[110\right]\mathrm{}$ are interpreted in terms of a modified Fermi-surface topology in close agreement with the most recent band-structure calculation of Callaway and Wang, which produces interference areas close to the observed new frequencies. These frequencies exhibit large second-harmonic amplitudes, and preliminary results on the temperature dependence of the amplitudes show a reduced temperature dependence, as expected for interference areas fed by open orbits. Closed-orbit magnetoresistance oscillations are also observed at frequencies close to those previously reported in dHvA experiments. These have large amplitudes for field directions corresponding to open-orbit minima and suggest amplitude enhancement by Landau-level modulation of magnetic breakdown gaps connected to the open-orbit network. The ac magnetoresistance results show the presence of closely spaced frequencies due to open-orbit interferences and closed orbits, which resolves questions from the dc results where only one frequency was resolved at a value shifted from dHvA results.