We have used a torque magnetometer to measure de Haas - van Alphen oscillations in the magnetization of two-dimensional electrons in GaAs/AlGaAs heterostructures and multiple-quantum-well systems for temperatures ranging from 0.125 K to 4.2 K and in magnetic fields of up to 15 T. Our results indicate that for high magnetic fields the density of states can be described by a series of Lorentzian-broadened Landau levels with a broadening that is independent of the magnetic field, B, and Landau level index, n. However, at low magnetic fields the Lorentzian-broadened density of states becomes indistinguishable from a Gaussian one with a broadening that is proportional to . The high-field behaviour of the Landau level line-shape is shown to differ appreciably from the low-field case as reported by other workers using both magnetization and other experimental methods. The reliability of this and other experimental techniques is discussed.

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The EPR spectrum at 9.1 GHz of the M = l/2~-l/2 transition for Mn2+ in polycrystalline dolomite has been studied using a detailed computer simulation of the line shapes in the powder pattern spectrum. The accuracy of the analytical procedure was verified for the spectrum of Mn2+ in calcite, yielding magnetic constants which were in excellent agreement with previous polycrystalline and single crystal results. The EPR parameters obtained for Mn2+ in dolomite are g = 2.0020(2), A = -9.48(2) mT for Mn 2 + substituted in the Ca lattice site and g = 2.0028(2), A = -9.25(2) mT, D = 14.60(5) mT for substitution at the Mg site.

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