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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.

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.

Process of the solid-phase diffusion of manganese into single crystals ZnGeP2 are investigated by electron paramagnetic resonance and X-ray element microanalysis. Conditions for formation of a solid solution with Mn2+ concentration of 1018 cm-3 were found. A diffusion coefficient of manganese in single crystal of ZnGeP2 at a diffusion annealing temperature was determined.

A low-temperature (3–100 K) electron spin resonance (ESR) study of the spin system of neutral As donors in Ge showed that on the insulator side of the insulator-metal transition the single-spin density exponentially disappears as T → 0. Such spins are bound into pairs to give an antiferromagnetic (AF) phase. Upon increasing the temperature the AF phase is destroyed, the single-spin density and, as a result, the ESR absorption signal becomes stronger. The temperature dependences of the densities of the pairs and single spins are typical for a chaotic distribution of neutral donors. In this case, there is no Neel temperature. For a low degree of compensation, the crystal lattice of Ge with the AF phase is actually a nanostructured system characterized by anisotropic internal stresses that are the strongest along one of the [110] directions. These stresses give rise to the anisotropy of the g-factor which is responsible for experimentally observed splitting of the ESR line. The compensating impurities destroy the AF phase and reduce this splitting. Local stresses are present in this case, too, but now they appear because of the Coulomb interaction of oppositely charged impurities and have no preferred orientation.

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.

It is shown that, on the insulator side of the insulator – metal transition, the single spin density exponentially disappears as T 0. Such spins are bound into pairs to give an antiferromagnetic (AFM) phase. Upon an increase in temperature the AFM phase is destroyed, the single-spin density, and, as a result, ESR absorption signal becomes stronger. The temperature dependencies of the densities of the pairs and single spins are typical of a chaotic distribution of neutral donors. In this case, there is no Neel temperature. In low degree of compensation, the crystal lattice of Ge with the AFM phase is actually a nanostructured system characterized by anisotropic internal stresses that are the strongest along one of the [110] directions. These stresses give rise to anisotropy of the g-factor which is responsible for experimentally observed splitting of the ESR line. The compensating impurities destroy the AFM phase and reduce this splitting. Local stresses are present in this case, too, but now they appear because of the Coulomb interaction of oppositely charged impurities and have no preferred orientation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

We show for n -type semiconductors, using Ge:As and 4H -SiC:N as examples, that the spin density measured by electron spin resonance (ESR) falls sharply near the insulator–metal (IM) transition. Two reasons might be responsible for this phenomenon: potential fluctuations with concentration of the electrons in local minima or local antiferromagnetic spin pairing (“spin glass”) in the insulating state just below the IM transition. In the investigated semiconductors manifestation of the latter is observed as a change from Curie to a Curie–Weiss behaviour with negative constant Θ. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The first observation of low temperature magnetoresistance (MR) of interference nature in the case of a light doping is reported. This MR occurs in both n- and p-type Ge samples in weak magnetic fields at frequency of 10 GHz and temperatures below 30 K. It is registered on the background of the classical MR effect associated with electrons in different valleys of n-Ge and with different (heavy and light) holes of p-Ge. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The first observation of low-temperature magnetoresistance (MR) of interference nature in the case of a light doping is reported. The MR occurs in n- and p-type Ge samples at a frequency of 10 GHz at temperatures below 30 K in weak magnetic fields on the background of the classical MR effect associated with electrons in different valleys (n-Ge) and with heavy and light holes (p-Ge).

Ternary diamond-like compounds in II–IV–V2 semiconductor system heavily-doped with transition d-element Mn have been recently prepared. The materials grown in both forms — single crystal layers and polycrystalline bulks — exhibit well defined ferromagnetic hysteresis with a saturation behavior in the magnetization curve up to above room temperature. Curie temperatures are of TC=310 K to 320 K for ( Cd 1-x Mn x) GeP 2 and ( Zn 1-x Mn x) GeP 2 compounds. The chemical states in the bulk of ZnGeP 2: Mn and interface of Mn -doped ferromagnetic layer on ZnGeP 2 (001) crystal, have been clarified by electron paramagnetic resonance and in situ photoemission spectroscopy. The as-prepared surface consists of Ge -rich, metallic Mn -compound. In and below the sub-surface region, dilute Mn 2+ species as precursors of the DMS phase exist. Mn 2+ ions are paramagnetic active on Zn 2+ sites in the bulk and show five EPR sets of equidistant peaks. Theoretical band-gap calculation suggests a predominant antiferromagnetic order in stoichiometric ( Cd , Mn ) GeP 2 but the systems with vacancies as ( Cd , V C , Mn ) GeP 2 or ( Cd , Ge , Mn ) GeP 2 are ferromagnetic and energetically stable. These materials are of great promise for room-temperature spintronics applications.

The electron spin resonance investigation in the insulator phase of compensated n-Ge:As shows that near the insulator–metal transition the weakly localized electrons are connected in the pairs with the antiparallel coupled spins. As a result, the antiferromagnetic spin glass structure is produced. The main manifestations of the phenomenon are the fall of the (free) spin density and a g-factor shift to the strong magnetic field with the electron concentration growth in the pretransition range. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Anomalously intense dispersion has been observed in the magnetic resonance signals of manganese clusters in the chalcopyrite crystal ZnGeP 2 :Mn with a high concentration of manganese. The EPR signals detected correspond to at least two types of isolated manganese ions. One of these apparently possesses acceptor properties, which makes manganese a self-contained impurity for the formation of a ferromagnetic state in accordance with recent theoretical predictions.

Magnetic properties of a volumetric area in the heterosystem of ferromagnetic (Zn,Mn,Ge)P 2 —diamagnetic ZnGeP 2 have been studied. The formation of the ferromagnetic layer on the surface of ZnGeP 2 crystal accompanies with Mn-diffusion inward the crystal bulk. Manganese penetrates deep into the crystal and occupies Zn sites in the chalcopyrite lattice. Mn 2+ ions are paramagnetic active in the sites and show five EPR sets of equidistant peaks. Photo-EPR spectra discover optically active behavior of point defects likely V P in ZnGeP 2 and (Zn,Mn,Ge)P 2 at low temperatures. The defects have a tetrahedral symmetry and are surrounded with four phosphorus atoms. The measurement of magnetization M versus temperature T at zero-field-cooling results in Curie temperature of T C =318 K . The low temperature M ( T ) dependence displays uneven feature ascribed to competitive the second magnetic sublattice in (Zn,Mn,Ge)P 2 due to Mn ions in a different valence state.

Anomalously intense dispersion was observed in the magnetic resonance signals of manganese clusters in the chalcopyrite crystal ZnGeP2:Mn with a high concentration of manganese. The EPR signals detected corresponded to two types of isolated manganese ions. One of these apparently possesses acceptor properties, which makes manganese a self-contained impurity for the formation of a ferromagnetic state in accordance with recent theoretical predictions.

The effect of an elastic spontaneous distortion of the crystal lattice of a doped semiconductor Ge:As was observed near the insulator–metal (IM) phase transition. The effect was discovered in a study of the electron spin resonance at electron concentrations 0.8≤ n / n C ≤1 ( n C =3.7×10 17 cm −3 is the critical electron density for the IM phase transition) at low temperatures T ≤100 K. A study demonstrated that the phenomenon can be understood in terms of the Peierls model of a spin transition in the disordered spin system of the semiconductor. The spin-Peierls transition gives rise to a new type of defects in doped uncompensated or weakly compensated n-type semiconductor in the form of a domain structure.

The study of the electron paramagnetic resonance in Ge:As has revealed that the insulating state in uncompensated semiconductors is preserved near the insulator-metal phase transition because of the appearance of lattice distortions. The latter are caused by the interaction of the spins localized on impurity atoms due to the spin-Peierls transition. In Ge:As, this effect manifests itself in the concentration range n = n = 3 × 1017–3.7 × 1017 cm−3.

Diamond-like ZnGeP2 single crystals with a chalcopyrite structure highly doped with manganese have been obtained by means of reactive solid-phase diffusion. According to the EPR data, the concentration of Mn2+ ions reaches up to 1017−1018 cm−3.

The low-temperature transformation from antiparallel to parallel spin orientation in a nonmagnetic compensated system Ge:As semiconductor near the metal-insulator phase transition has been experimentally observed. This effect is manifested in the temperature dependences of the impurity magnetic susceptibility obtained by integration of the spin resonance absorption line. These dependences show that the spin density falls in the medium temperature range (10-100 K) and grows at low temperatures. The effect is confirmed by the specific temperature features of the g-factor and inverse magnetic susceptibility. As the relative content of a compensating impurity (gallium) is made lower than 0.7, the transition temperature begins to decrease and, at a degree of compensation < 0.3, falls outside the temperature range under study (i.e., below 2 K).

Behavior of the paramagnetic susceptibility in Si:P at low temperatures was investigated by Electron Spin Resonance in order to detect the antiferromagnetic and ferromagnetic ordering in the vicinity of the insulator-metal phase transition. A procedure was developed to operate sufficiently smooth changes of the spin density, by proton irradiated.

Spontaneous crystallization from a solution in a melt at a pressure of (0.8–1)×10−3 Pa was used to obtain single crystals of a new nonperovskite-like superconducting phase Ba2Cu3O6−x space group P ccm, a=13.065, b=20.654, and c=11.431 A). The superconducting properties of the crystals were investigated by modulated microwave absorption. The superconducting transition temperatures were 5 K (sample No. 1), 7 K and 13 K (sample No. 2). The superconductivity in the Ba2Cu3O6−x crystals is attributed to the presence of CuO2 chains of edge-sharing copper-oxygen squares. Nonperovskite-like Ba2Cu3O6−x crystals are a new class of one-dimensional (1D) superconductors.

Method for determining the magnetic susceptibility in the high doped semiconductors is considered. A procedure that is based on double integration of the positive part of the derivative of the absorption line having a Dyson shape and takes into account the depth of the skin layer is described. Analysis is made for the example of arsenic doped germanium samples at a rather high concentration corresponding to the insulator metal phase transition., Pages 13, figures 9, references 10

Electron paramagnetic (EPR) and ferromagnetic resonance (FMR) have been studied in the system of (Zn,Mn)GeP2 ferromagnetic layer grown on undoped ZnGeP2 single crystal. Strong FMR signals are registered in the wide temperature range up to room temperature. EPR and photo-EPR of intrinsic defects are observed in ZnGeP2 substrate. EPR spectra characteristic of Mn2+ ions on Zn2+ sites in the bulk appear after the growth of the ferromagnetic layer on ZnGeP2 crystal indicating the efficient Mn-diffusion into the bulk crystal by the annealing treatments.

A problem of the final time of the effective mass averaging in the system of light and heavy holes is manifested in a study of magnetoresistance (MR) in p‐Ge at low temperatures and a frequency of 10 GHz. It is shown that the effective mass averaging takes place in the time which is more than 10−10 sec and is significantly more than the time of momentum relaxation. The experimentally estimated averaging time turned out to be connected with the time of the energy relaxation.

A study of the electron spin resonance in Ge:As revealed that, in uncompensated semiconductors with shallow impurity levels, the insulator state is preserved near the insulator‐metal phase transition because of the appearance of lattice distortions caused by interaction of spins localized on impurity atoms. We consider this effect as variation of the spin‐Peierls transition. In Ge:As, this effect is manifested at carrier concentrations n = 3×1017–3.7×1017 cm−3. Owing to the random distribution of impurities in the Ge lattice, the properties of this transition differ from those of a similar transition in substances in which uncompensated spins are localized on constituent ions of the host lattice.

Low-temperature magnetic susceptibility of heavily doped Ge: As samples has been investigated by methods SQUID magnetometry and ESR spectroscopy near the metal-insulator phase transition. Paramagnetic component of the impurity magnetic susceptibility was investigated by ESR previously. Using both techniques make possible to determined the diamagnetic component of impurity susceptibility. The value of the impurity diamagnetic susceptibility equals to 5×10-8 cm3/g and corresponds to the localization radius of the As donor- electron near the metal-insulator phase transition.

The influence of the conditions of synthesis and annealing on the ratio of the volumes and the temperature Tcn at which transition to the superconducting state begins is investigated on the basis of diamagnetic susceptibility measurements and x-ray phase analysis for bismuth 2212 and 2223 phases obtained from solution in a KCl melt. It is found that the value of Tcn for the 2212 phase decreases as the temperature and the holding time are increased in synthesis. The 2212–2223 transition in the fluxed KCl melt takes place in the presence of an oxygen deficiency, and the width of the transition interval to the superconducting state of the 2223 phase depends on the cooling rate of the fluxed melt after isothermal holding and also on subsequent annealing in air. Temperatures Tcn=107 K, 90 K, and 20 K are observed for unannealed crystals of the 2223 phase with average dimensions 50×50 µm. Air annealing leads to oxygen saturation of their lattice, and Tcn=107 K throughout the entire structure of the crystal.

Electron spin resonance investigation in the insulator phase of compensated n‐Ge:As shows that near the insulator — metal transition the weakly localized electrons are connected in the pairs with the antiparallel coupled spins. As a result, the antiferromagnetic spin glass structure is created. The main manifestations of the phenomenon are the fall of the free (unpaired) spin density, the free spin increase with temperature, and characteristic antiferromagnetic g‐factor shift with the electron density in the pretransition range.

The anomalous magnetoresistance (MR) of the interference origin was first observed in the weakly doped nongenerated n‐Ge:Sb and p‐Ge:Ga. Early proposed for the MR detection, the electron spin resonance technique was used for this investigation. It was found that the anomalous MR was observed in these materials in the temperature range of the classical (nonhopping) motion and in the magnetic fields not higher than some hundred Oersteds. Some peculiarities of the classical MR were observed and explained too.

The microwave low temperature magnetoresistivity of the low doped (nondegenerated) p-Ge was investigated with the use of the electron spin resonance technique. This technique permits to detect the derivative of the microwave absorption with respect to magnetic field and its change with this field. In our case, this change is proportional to the magnetoconductivity of the sample under investigation. Because of the averaging time of the effective masses of the light and heavy holes is much more then microwave frequency (10 GHz), this method permits to investigate the reaction of the each kind of the holes on the magnetic field separately. The experimental results are compared with the theory of the classical magnetoresistivity effect.

Impurity paramagnetic susceptibility of n-Ge has been measured in the vicinity of the insulator– metal phase transition by two techniques: ESR and SQUID. A comparison of these methods demonstrated that their results qualitatively coincide at low temperatures, but differ at high temperatures. The advantage of the ESR technique is in its substantially higher relative precision, but SQUID makes it possible to obtain on principle absolute values of the magnetic susceptibility. It was found that, in the present-day state of development, the SQUID method has a substantially poorer precision, compared with ESR

The structure and properties of GaAs layers grown by molecular-beam epitaxy at low temperature (150-250 °C) have been studied. The samples were found to contain up to 1.5 at.% extra As, which formed nano-scale clusters under annealing. The dependences of the excessive As concentration and As-cluster size and density on the growth and annealing conditions were established. LT-GaAs layers were found to have high electrical resistivity, however, our investigations of microwave absorption in a weak magnetic field revealed a characteristic signal usually attributed to the superconducting phase. It has been proved that this microwave absorption is unlikely to be due to either the arsenic clusters in LT-GaAs films or indium in the substrate, as it was assumed previously. We suggest a new hypothesis that the superconducting phase in LT-GaAs is Ga nanoclusters formed on the growth surface.

A study of the electron spin resonance in Ge:As revealed that, in uncompensated semiconductors with shallow impurity levels, the insulator state is preserved near the insulator-metal phase transition because of the appearance of lattice distortions caused by interaction of spins localized on impurity atoms and the resulting spin-Peierls transition. In Ge:As, this effect is manifested at carrier concentrations n = 3 1017–3.7 1017 cm-3. Owing to the random distribution of impurities in the Ge lattice, the properties of this transition differ from those of a similar transition in substances in which uncompensated spins are localized on constituent ions of the host lattice.