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We present the results of structural characterization of Cd1 � xMnxGeAs2 chalcopyrite-type crystals with low Mn content x varying from 0 to 0.037. High resolution X-ray powder diffraction method of measurements and Rietveld refinements procedure used for analysis of obtained diffraction patterns revealed high crystal quality of the samples. The substitutional alloying of Cd1 � xMnxGeAs2, with Mn ions at Cd sites, has been confirmed. The analytical equations describing the linear reduction of the lattice parameters with increase of Mn content were deduced and compared with the literature results of theoretically estimated lattice parameters of compounds of the same kind. Copyright © 2015 John Wiley & Sons, Ltd.

The systematic magnetic and structural properties of as-prepared, “Fe” catalyst based multiwalled carbon nanotubes (MWCNTs), and chemically modified MWCNTs were studied. The structural characterization by means of transmission electron microscopy, X-ray diffraction, and Raman spectroscopy was performed. DC magnetization up to 9 T was studied. We examined the influence of chemical treatment (purification procedure) on the magnetic properties of MWCNT's. The significant changes in the saturation magnetization after chemical treatment were observed. However, we noticed high magnetic coercivity values for as-prepared as well as chemically modified samples.

The systematic studies of both magnetic and magnetotransport properties of Zn 0.947 Mn 0.053 GeAs 2 diluted magnetic semiconductor are presented. The paramagnetic behaviour of the sample confirms that the solubility of Mn in the studied alloy is of the order of 5 at%. The Curie―Weiss behaviour of magnetic susceptibility is preserved only at low temperatures, T < 100 K indicating the presence of short-range magnetic interactions in the system due to the presence of groups of Mn counting few ions. The high-field magnetization together with magnetoresistance data is used to estimate the amount of magnetic ions active in the semiconductor matrix. The obtained results showed that the amount of magnetically active Mn ions in the semiconductors matrix is two orders of magnitude lower than the value obtained from X-ray fluorescence measurements. The magnetotransport studies revealed that only about 30% of all Mn ions are electrically active in the semiconductor matrix.

In this paper we report on the crystal growth and magnetic as well as structural studies of SiC: Fe. SiC crystals were grown by Physical Vapor Transport method. We used Fe enriched source material to dope crystals. The magnetic properties were examined by AC/DC magnetometry. AC magnetic susceptibility as well as DC magnetization measurements revealed ferromagnetic type of magnetic ordering. The structural measurements using powder X-ray diffraction were performed.

Low-temperature charge-carrier transport in simple magnetoresistive nanodevices, consisted of narrow constrictions of submicron width in the epitaxial layer of a ferromagnetic (Ga,Mn)As semiconductor, has been investigated and correlated with magnetic properties of the layer. The devices containing constrictions; revealed abrupt jumps of a reduced resistance that appeared when the sweeping magnetic field crossed the regions of the coercive field of the layer magnetization. In contrast, the non-constricted reference device displayed abrupt jumps of an enhanced resistance at the same values of magnetic field. We interpret the both features, whose positions on the magnetic-field scale reflect the hysteresis loop of magnetization, as manifestation of domain wall contribution to the (Ga,Mn)As layer resistance. The negative contribution of a domain wall to the resistance in the constricted device results most likely from the suppression of the weak localization effects by a domain wall located at the constriction. (Less)

ZnO and ZnMnO doped with N and/or As layers were fabricated by thermal oxidation of ZnTe and ZnMnTe grown by MBE on different substrates. The Hall measurements demonstrated p -type conductivity with the hole concentration of ∼5 · 1019 cm–3 for ZnO:As and ZnO:As:N on GaAs substrates and ∼ 6 · 1017 cm–3 for ZnTe:N on ZnTe substrates. Optical study showed meaningful differences between samples with different acceptor, grown on different substrates. Magnetoptical experiment demonstration Zeeman splitting in ZnMnO samples. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Using quasi-chemical reaction methods, we calculated concentrations of equilibrium defects for zinc selenide crystals doped with ZnSe〈Te〉 during the growth process and with ZnSe:Te from the vapour phase. It was found that the main irradiation peak at ħωm ≈1.7 eV for ZnSe〈Te〉 samples is defined with the associates formed by single-charge intrinsic defects – positive interstitial zinc atoms and its negative vacancies . These vacancies, reaching the concentrations of 1022 cm–3 in ZnSe:Te crystals, are also responsible for the luminescence and absorption peaks at the energies of 2.4 eV. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

MnTe layers of high crystalline quality were grown on Al2O3 substrates (0001)-oriented by molecular beam epitaxy (MBE). Characterization of MnTe by X-ray diffraction (XRD) revealed a hexagonal structure of NiAs-type with lattice parameters a = 4.166 A and c = 6.694 A. The energy gap of MnTe, evaluated from the optical transmission spectra measured at 10 K, was found to be 1.7 eV. The Neel temperature obtained from neutron diffraction (ND) measurements was 284.1 K. ZnO:N layers were fabricated by thermal oxidation of metallic Zn and ZnTe grown by MBE on different substrates. In order to achieve p-type conductivity, the starting materials were doped by nitrogen. The XRD spectra of the oxidized samples showed peaks related to hexagonal ZnO. The Hall measurements demonstrated p-type conductivity with the hole concentration of ∼2.2 × 1019 cm–3 and ∼6.7 × 1017 cm–3 for ZnO:N deposited on GaAs and ZnTe, respectively. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Successful growth of the ZnO and ZnO:Mn crystals by the CVT method and their characterisation are reported. The source material was synthesized at 650 °C from oxygen and zinc vapours and subsequently – baked (as a powder) to achieve stoichiometry. Crystal growth (at ∼1100 °C, with the rate ∼1–2 mm/day) proceeded in graphite-covered quartz ampoules containing pure (6N) hydrogen or nitrogen or chlorine and a little of water vapour and carbon. The crystals, both as-grown and annealed in pure oxygen, were characterised by the measurements of: transmission spectra in energy gap and far infrared regions, photoluminescence and reflectivity spectra, electrical transport properties and EDXRF – the energy dispersive X-ray fluorescence (for Mn content determination). In the surface region – the impurities and the Mn content were studied by the secondary ion mass spectroscopy (SIMS). Manganese and native defects (VO) were investigated by electron paramagnetic resonance (EPR) and Raman spectroscopy. Results of the measurements are presented and discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present a general approach to the problem of a ferromagnetic phase transition in diluted magnetic semiconductors with free carriers. The Curie temperature of ferromagnetic transition is calculated in the mean field approximation. The approach allows to analyze the effects of magnetic fluctuations and disorder on the Curie temperature. We also propose a new mechanism of exchange interaction between magnetic impurities at vanishing concentration of free carriers.

In some IV-VI semimagnetic semiconductors, the RKKY interaction can dominate over the standard d-d superexchange and become the driving mechanism for ion-ion coupling. In effect, for low hole concentrations the Mn ion system is in a paramagnetic phase, whereas for higher ones it reveals typical ferromagnetic behavior. In this paper, recent work on IV-VI ferromagnetic (SnMnTe, PbSnMnTe and GeMnTe) systems will be presented. In particular, the influence of the presence of two types of magnetic ions (transition metal: Mn and rare earth metal: Eu or Er) incorporated into a semiconductor matrix on magnetic properties of resultant semimagnetic semiconductor will be described.

Publisher Summary This chapter discusses low-dimensional structures of II–VI diluted magnetic semiconductors (DMS) with manganese and describes the carrier concentration induced ferromagnetism in Mn-based IV–VI DMS with a particular emphasis on Mn content and conducting hole concentration dependent paramagnetic–ferromagnetic–spin glass transitions in bulk crystals and thin layers of SnMnTe and related materials. The chapter also discusses the transport, magnetic, and optical properties of bulk crystals and thick epitaxial layers; low-dimensional quantum structures of IV–VI DMS with Eu; the magnetic and electrical properties of IV–VI semiconductors with Gd; and the magnetic and optical properties of all semiconductor ferromagnetic multilayers built of ferromagnetic EuS and nonmagnetic IV–VI (PbSe and PbS) semiconductors. The chapter describes DMS containing transition metals other than manganese. These materials never attracted as much attention as the ones containing Mn, mainly because of severe difficulties in their preparation, particularly when large percentages of the magnetic components were involved.

The Shubnikov-de Hass effect (SdH) is investigated in n-type Hgl−xMnxTe mixed crystals for several compositions in the range 0.02 ≦ x ≦ 0.04. Experiments are carried out on samples with electron concentrations between 2 × 1015 and 8.5 × 1017 cm−3 at temperatures from 2 to 25 K. Prom the temperature dependence of the amplitude of the SdH oscillations the effective masses of electrons are determined. The data are analyzed in terms of a model developed to account for anomalies observed earlier in the SdH effect in this material. Der Shubnikov-de Haas-Effekt (SdH) wird in n-leitenden Hg1−xMnx Te-Mischkristallen fur verschiedene Zusammensetzungen im Bereich 0,02 ≦ x ≦ 0,04 untersucht. Die Experimente werden an Proben mit Elektronenkonzentrationen zwischen 2 × 1015 und 8,5 × 1017 cm−3 bei Temperaturen von 2 bis 25 K durchgefuhrt. Aus der Temperaturabhlingigkeit der Amplitude der SdH-Oszillationen werden die effektiven Massen der Elektronen bestimmt. Die Werte werden mit einem Modell analysiert, das zur Erklarung der Anomalien entwickelt wurde, die schon fruher fur den SdH-Effekt in diesem Material beobachtet wurden.

Measurements are made of the Shubnikov-de Haas (SdH) effect at 4.2 K up to 180 kOe in HgSe samples with electron concentration in the range 1.7 × 1017 to 2.2 × 1018 cm−3. The theoretical analysis is based on the Pidgeon and Brown model. The spin splitting of SdH oscillations shows an angular dependence. The anisotropy of the spin splitting exceeds 15% between and direction and depends on energy and the quantum number of the Landau levels. The theory gives satisfactory agreement with the experimental data. A new set of band structure parameters is established. Additional peaks in SdH oscillations, which are not predicted by the model, are also observed. Es wird der Shubnikov-de Haas (SdH)-Effekt bei 4,2 K bis zu Feldern von 180 kOe an HgSe-Proben mit einer Elektronenkonzentration im Bereich zwischen 1,7 × 1017 und 2,2 × 1018 cm−3 gemessen. Die theoretische Analyse basiert auf dem Modell von Pidgeon und Brown. Die Spin-aufspaltung der SdH-Oszillationen zeigt eine Winkelabhangigkeit. Die Anisotropie der Spinauf-spaltung ubersteigt 15% zwischen und und hangt von der Energie und Quantenzahl der Landau-Niveaus ab. Die Theorie liefert befriedigende Ubereinstimmung mit den experimentellen Werten. Ein neuer Satz von Bandstrukturparametern wird aufgestellt. Zusatzliche Maxima der SdH-Oszillationen, die von dem Modell nicht vorhergesagt werden, werden ebenfalls beobach-tet.

Oscillations of the magnetoresistivity in CdvHg1−vSe for v = 0.05; 0.075; 0.10 and 0.19 are reported. From the temperaturedependence of the amplitudes of the oscillations, the effective mass of electrons was determined. The effective mass is dependent on concentration. In order to find the energy band gap, E0, and the matrix element, P, the k · p method, including interaction with higher bands and finite Δ, was used. It was foundthat the dependence of E0 on composition at 4.2 K is linear for v < 0.2. Es wird uber die Magnetowiderstandsanderung in CdvHg1−vSe fur v = 0,05; 0,075; 0,10 und 0,19 berichtet. Aus der Temperaturabhangigkeit der Amplituden der Oszillationen wurde die effektive Elektronenmasse berechnet. Die effektive Masse ist von der Konzentration abhangig. Um die Energiebandlucke E0 und das Matrixelement P zu finden, wurde die k · p-Methode unter Einschlus der Wechselwirkung mit hoheren Bandern und endlichem Δ benutzt. Es wurde gefunden, das die Abhangigkeit von E0 von der Konzentration bei 4,2 K fur v < 0,2 linear ist.