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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.

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.

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.