de Haas-van Alphen Effect in Iridium

Measurements of the de Haas-van Alphen (dHvA) extremal areas have been performed in three main symmetry planes of an Ir single crystal using magnetic fields up to 120 kG. A newly designed modulation-technique magnetometer was used in modulation and sample-rotation experiments; some measurements used the torque technique. Large torque or magnetization oscillations were observed from all four closed sheets of the Fermi surface predicted by the band-structure calculations of Andersen and Mackintosh. The measured cross-sectional areas of two hole sheets centered at $X$ in the Brillouin zone and called $X3\mathrm{}$ and $X4\mathrm{}$ were found to be, respectively, 30% smaller and 6% larger than the calculated ones. The observed areas of two electron sheets centered at $\Gamma$ were larger than the calculated ones by not more than 0.5%. The results agree with magnetoresistance data, confirming that Ir is an uncompensated metal and that its Fermi surface does not support open orbits. A few effective-mass values were determined from torque and modulation measurements of the temperature dependence of the amplitude of dHvA oscillations in magnetic fields up to 21 kG. A simulataneous determination of effective masses associated with two dHvA frequencies beating with each other was obtained. A spin-splitting zero was observed in the $\Gamma 6$ sheet in the (111) plane. The Dingle temperature was determined from the magnetic field dependence of the amplitude of torque oscillations. A generalized formula describing the magnetoresistance of an uncompensated metal was used to calibrate a copper-wire magnetoresistor for magnetic field measurements.