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Features of magnetic-field-dependent microwave absorption in HgSe samples doped with Co and Ni impurities in different concentrations are investigated. The electron-spin resonance spectra of weakly coupled Co atoms and peculiarities of the magnetic-absorption variation in a magnetic field passing through the zero value are established. The main parameters of the electron-spin resonance spectra and temperature and angular dependences of microwave absorption in weak fields are determined.

The electron-spin-resonance spectra of transition metal ions Fe in the HgSe matrix are analyzed. The spectra have an appearance typical of the Fe3+ ion, i.e., they consist of five fine-structure lines with a splitting that corresponds to a weak crystal field. The spectra are observed at temperatures of up to 50 K. The spectral lines are deformed and have a Dyson shape. An analysis of the temperature dependences of the line amplitudes shows that a transition from paramagnetic ordering to ferromagnetic ordering occurs with decreasing temperature, with the Curie temperature T ≈ 7 K.

Samples of a gapless HgSe semiconductor with different iron impurity concentrations are investigated. HgSe:Fe samples are examined by the electron-spin-resonance technique. Multiple resonance lines caused by unpaired spins of different origins are analyzed. The properties of electrons localized at shallow impurities are described using a hydrogen-like model. The effect of an internal field on the resonance lines is established. It is found that the conduction of HgSe is not only nonparabolic, but also nonspherical.

Magnetoresistance oscillations are considered in the case of microwave-radiation absorption in HgSe samples with a different Fe-impurity concentration. From the simultaneous analysis of the field and temperature dependences of the Shubnikov–de Haas oscillations, the effective mass, the Dingle temperature, and the quantum-limit field corresponding to the Fermi level are obtained. A method for analyzing the spectra with several oscillation frequencies, i.e., the beating effect, is proposed. The results are compared with data obtained by Hall measurements.

The low-temperature magnetoresistive effect in the semiconductor HgSe:Fe in weak magnetic fields at microwave frequencies is examined. The negative and positive components of magnetoabsorption based on the magnetoresistive effect in the degenerate conduction band are analyzed. The special features of experiments carried out in the investigated frequency range are noted. The momentum and electron-energy relaxation times are determined from the experimental field and temperature dependences.

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.

We consider a method for determining the magnetic susceptibility of “poor” conductors using electron paramagnetic resonance data. A method is described on the basis of double integration of the positive part of the derivative of the absorption line that has a Dyson shape. The skin depth is taken into account. Analysis is carried out for germanium samples doped by arsenic in the range of high concentrations corresponding to the insulator-metal transition.

The phenomenon of the low-temperature transition from antiferro- to ferromagnetic ordering of impurity spins in a nonmagnetic compensated n-Ge:As semiconductor near the metal-insulator phase transformation has been experimentally observed. The effect is manifested by rather sharp changes in the spin density and g-factor in the electron spin resonance spectra. As the relative content of a compensating impurity (gallium) is reduced below 0.7, the transition temperature begins to decrease and, at a degree of compensation below 0.3, drops below the studied temperature range (i.e., below 2 K).

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.

To determine the electronic properties of metal-carbon clusters, palladium clusters are introduced into nanoporous carbon samples. The structural and magnetic properties of the nanocomposite thus obtained are investigated. A ferromagnetic resonance (FMR) component is observed in the electron spin resonance (ESR) spectra measured in a wide temperature range. The electron density of states (DOS) of clusters consisting of a palladium atom surrounded by carbon atoms is calculated, and it is shown that, due to the interaction between electronic terms of carbon and metal, such a cluster should exhibit magnetism. The investigation of the structures of the porous skeleton of nanoporous carbon and of palladium clusters has allowed us to reveal how carbon and palladium atoms are brought into close contact so that to give rise to the observed ferromagnetism.

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.

Cobalt clusters were embedded into a nanoporous carbon powder (with pores about 2 nm in size) prepared from a B4C carbide powder. Electron spin resonance (ESR) measurements were carried out within a broad temperature range. At all temperatures, the ESR spectrum consisted of two overlapping resonance Lorentzian lines. The temperature dependences of the integrated intensities and linewidths and of the resonance fields were determined. A theoretical analysis of these dependences shows that they can be described in terms of the theory of a disordered magnetic medium with two spin systems with different properties.

The variation in the width and shape of the ESR line of nitrogen in 4H-SiC in the concentration range corresponding to the insulator-metal phase transition was investigated. It is shown that the spin relaxation in the region of hopping and metal conduction occurs at electrical multipoles (clusters) whose sizes decrease from rather large to small (characteristic of interimpurity distances) as the concentration of impurity centers increases. Analysis of the temperature dependences of the resistance made it possible to estimate the critical concentration for the insulator-metal phase transition (ND-NA)c≈1.5×1019 cm−3. The values of other characteristic concentrations that determine the effects of electron-electron interaction in the system under study were also found.

Special features of electron spin resonance in the vicinity of the insulator-metal phase transition in n-type 4H-SiC:N were investigated. It was shown that, in the insulating state, an antiferromagnetic phase of the spin-glass type is formed in this region. As a result, with increasing doping level, the content of the paramagnetic phase decreases, and, at an impurity concentration close to critical (corresponding to the transition), the resonance line of nitrogen atoms disappears. Instead of it, a line of deep-level impurity centers is observed at the same position in the metallic state. In addition, two new lines are observed in the metallic state in strong fields; these lines are attributed to free charge carriers.

Measurements of the electrophysical properties of nanoporous carbon (NPC) samples (conductivity and Hall effect), as well as studies of the same samples using electron spin resonance (ESR), are summarized. Free holes are shown to play the major part in charge transport in such materials, thus permitting identification of the ESR signal with free holes. An analysis of the shape of the resonance lines, as well as of their dependence on temperature and the technology employed in sample preparation, established the ESR signals to consist of two superimposed resonance lines associated with carriers, free or localized to various extents, whose magnetic susceptibility obeys Pauli and Curie-Weiss laws, respectively. The temperature dependences of the ESR signal parameters were studied, and the experimental relations were compared with theory to determine the model-parameters. An analysis of the temperature behavior of these parameters suggests the conclusion that NPC samples are heterophase porous systems whose properties are dominated by structural characteristics.

The microwave magnetoresistance (MR) of neutron transmutation doped (moderately compensated) Ge:Ga in the insulator-metal transition region was studied using ESR technique. As the hole concentration increases, the MR mechanism changes in the insulator state near the phase transition point: the hopping conductivity that is characterized by the impurity wave-function contraction by the magnetic field is replaced by the state of weak localization. In the latter case, the temperature dependence of the diffusion coefficient is of great importance near the transition point (1.2×1017 cm−3). This dependence decreases in the metallic state. In the metallic state, the diffusion coefficient is independent of temperature and the MR temperature dependence is described by the dephasing mechanism due to phonon scattering. The electron-electron interaction contribution to the dephasing time should be considered for heavier doping.

Capacitance-related methods and electron spin resonance were used to study the deep-level centers formed in n-4H-SiC as a result of irradiation with 8-MeV protons. For the samples, Schottky diodes and p-n structures formed on the layers either obtained by sublimational epitaxy or produced commercially by CREE Inc. (United States) were used. It was found that the type of centers introduced by irradiation is independent of the technology of the material growth and the type of charged particles. On the basis of the results of annealing the defects and the data of electron spin resonance, the possible structure of the centers is suggested.

Capacitance methods and electron spin resonance (ESR) were applied to study deep centers in n-6H-SiC irradiated with 8 MeV protons. Schottky diodes and p-n structures grown by sublimation epitaxy or commercially produced by CREE Inc. (United States) were used. The type of the irradiation-induced centers is independent of the material fabrication technology and the kind of charged particles used. Irradiation results in an increase in the total concentration of donor centers. The possible structure of the centers is suggested on the basis of data on defect annealing and ESR.

The magnetoresistance of heavily doped Ge:As near the metal-insulator phase transition has been studied both on the metal and insulator sides of the transition. Measurements were made at microwave frequencies using a noncontact technique of electron spin resonance. The field and temperature dependences of the magnetoresistance derivative in metallic samples reveal two main features of the phenomenon: a negative magnetoresistance at weak fields, due to the weak localization effect, and a positive magnetoresistance at strong fields, arising from the electron-electron interaction in the diffusion channel. Only a weak negative magnetoresistance with a characteristic low-field behavior is observed in insulating samples. The results are compared with the theory of quantum corrections.

Electron spin resonance (ESR) is investigated in the vicinity of metal-insulator transition in compensated n-Ge:As. It is found that the 10-GHz signal is observed from both sides of the transition up to a temperature of 100 K. ESR spectrum in metallic samples looks like a single line of the Dyson type, with the line shape varying with temperature. The Dyson line in the insulating samples transforms into the Lorentz line which splits into two lines at temperatures below 4.1 K. One line has an ordinary shape, the other has an anomalous step-like shape in the magnetic field, increasing with decreasing temperature. This effect has not been satisfactorily explained so far. Two mechanisms are proposed for the spin relaxation observed, one of which is related to donor-acceptor pairs and the other, to phonons. The Pauli and Curie paramagnetism is found in metallic and insulator samples, respectively.

Magnetic-field-dependent microwave absorption and electron spin resonance are used to investigate magnetoresistive effects in strongly doped n-InAs. It is shown that these effects can be traced back to negative, positive, or oscillatory magnetoresistance (i.e., the Shubnikov-de Haas effect). While the experimental data are in agreement with the predictions of theory in the latter two cases, for the negative magnetoresistance there are features that are difficult to interpret, especially the absence of any effect at very small fields, much smaller than the characteristic field Hϕ that appears in the theory of quantum corrections, and the two-dimensionality of bulk samples in fields much larger than Hϕ implied by the observed dependences on temperature and to some extent on the magnetic field.

The magnetoresistance of a lightly doped p-Ge1−x Six alloy is studied in the range of compositions x = 1–2 at %. The results are compared with the available data for lightly doped p-Ge. The studies have been carried out using ESR measurements at a frequency of 10 GHz in the temperature range 10–120 K. It is established that micrononuniformity in the distribution of Si in the Ge lattice (Si clusters) suppresses the interference part of the anomalous magnetoresistance and, in addition, results in an averaging of the effects of light and heavy holes. This observation suggests a sharp decrease in the inelastic scattering time in the case of a Ge1−x Six solid solution as compared to that of Ge.