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The method of superconducting quantum interference device (SQUID) magnetometry is used to measure and study low-temperature (T ≤ 100K) susceptibility in a series of samples of heavily doped Ge:As samples on the insulator side of the insulator–metal phase transition. Subtracting the known values of the magnetic susceptibility of the lattice from the measurement results, the values of the impurity magnetic susceptibility of the system are obtained. Using the method of electron spin resonance, the paramagnetic component of the impurity susceptibility is determined. Subtraction of the paramagnetic component from the total impurity susceptibility is used to obtain, for the first time, the values of the impurity diamagnetic susceptibility (~5 × 10–8 cm3/g). The obtained result is consistent with estimates obtained for the localization radius of an electron at an As donor. Lowering the temperature to T ≤ 4 K leads to an increase in the diamagnetic susceptibility, which is consistent with the observed increase in the paramagnetic susceptibility. The observed effect is accounted for by the transition of impurity electrons from the singlet state to the triplet one.

The microwave magnetoresistivity of lightly doped (nondegenerate) p-Ge has been studied by the electron spin resonance method. This technique can be employed to record the derivative of the microwave absorption with respect to the magnetic field on the assumption that changes in this absorption are proportional to changes in the conductivity of a semiconductor. At the 10-GHz frequency of the electromagnetic field, the averaging time of the effective masses of light and heavy holes at low temperatures is substantially longer than the oscillation period. This makes it possible to study the individual responses of light and heavy holes to the magnetic field. It is shown that the microwave magnetoabsorption associated with light holes only slightly depends on the direction of the magnetic field relative to the crystallographic axes of Ge. At the same time, the signal related to heavy holes changes by several times when a sample is rotated in a magnetic field. The experimental results are correlated with the theory of the classical magnetoresistive effect.

A study of electron spin resonance in uncompensated Ge:As semiconductor samples in the vicinity of the insulator-metal second-order phase transiti on reveals that the interaction of spins localized at As atoms brings about a distortion of the crystal lattice and enhances the localization. This effect occurs in the range of electron concentrations n = 3 × 1017—3.7 × 1017 cm-3, just below the critical point of the phase transition. The effect is explained in the context of a model considering the spin-Peierls transition in the random impurity sublattice of the semiconductor, and its features, as compared to other known materials where the spin-Peierls transition is observed, are understood.

The effect of spin interaction on the width and shape of the electron spin resonance line in compensated and uncompensated n-Ge:As has been studied. It is shown that, in the case of a magnetic field oriented along the [100] axis, the width of the resonance line decreases irrespective of the degree of compensation as the critical concentration of the insulator-metal transition is approached, owing to enhancement of the exchange interaction of spins and to an increase in the spin relaxation time. When the magnetic field is directed along other axes, an additional line broadening appears in compensated samples. This broadening is determined by the influence exerted on the g factor by fluctuations of the internal electrostatic field via the stresses generated by these fluctuations. For well-conducting samples, in which the thickness of the skin layer becomes smaller than that of the sample, the line takes on an asymmetric (Dysonian) shape. In this case, the ratio between the wings of the derivative, characteristic of this line shape, is determined by the ratio between the rates of spin diffusion and spin relaxation.

The changes in the spectrum and g factor of electron spin resonance due to the interaction of spins in the insulator state of n-Ge near the insulator-metal phase transition are studied. It is found that, in this region, the g factor decreases as the doping level is increased and exhibits anisotropy in the immediate vicinity of the transition. The effects of compensation and induced antiferromagnetic ordering on the g factor are analyzed. It is shown that, as the transition point is approached, the high-temperature limit of observation of the electron spin resonance rises sharply.