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We present studies of magnetotransport properties of Ge 1− x − y Pb x Mn y Te bulk crystals with chemical composition changing from 0.180 x y T SG around 90 K. The presence of strong anomalous Hall effect (AHE) with hysteresis is observed at T T SG . The data analysis allowed calculation of a correction to the Hall constant R H for T T SG and the AHE constant, R S . R S is around 10 −6 m 3 /C. R S and R H do not change strongly with temperature. The scaling law analysis has proved that the AHE in this system is due to the extrinsic mechanisms dominated by the skew scattering with relatively small contribution of the side jump process. Strong localization occurs in our system at T T SG and causes a presence of a minimum in the resistivity vs. temperature dependence. The magnetoresistance of our samples shows complex behavior at T T SG . The negative magnetoresistance is observed at T T nearly linear positive magnetoresistance is observed at temperatures from 20 K up to T ≈ T SG , where it reaches maximum. Positive linear magnetoresistance is related to the granular nature of our samples while the maximum near T SG is related to the giant spin-splitting of the valence band.

We present the studies of structural, magnetotransport, and magnetic properties of Ge1−x Eu x Te bulk crystals with the chemical composition, x, changing from 0.008 to 0.025. For the samples with x > 0.015 the sample synthesis leads to formation of Ge1−x Eu x Te spinodal decompositions with a broad range of chemical contents. The presence of Ge1−x Eu x Te spinodal decompositions is responsible for the antiferromagnetic order in our samples with x > 0.015. For the samples with x

We present studies of magnetic properties of Ge 1− x − y Pb x Mn y Te bulk crystals with chemical composition varying in the range of 0.180 x y J pd , having values from 0.47 eV to 0.80 eV gives spin-glass transition temperature, T SG , values close to the experimental values for the Ge-rich phase. The magnetic order observed for the Pb-rich phase is also due to the carrier mediated magnetic interaction. The experimental transition temperatures are fitted with J pd value ranging from 0.22 eV to 0.28 eV.

L. Kilanski, M. Szyma«ski, B. Brodowska, M. Gorska, R. Szymczak, A. Podgorni, A. Avdonin, A. Reszka, B.J. Kowalski, V. Domukhovski , M. Arciszewska, W. Dobrowolski, V.E. Slynko and E.I. Slynko Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warszawa, Poland Faculty of Materials Engineering, Warsaw University of Technology, Woaoska 141, 02-507 Warszawa, Poland Institute of Materials Science Problems, Ukrainian Academy of Sciences, 5 Wilde Str., 274001 Chernovtsy, Ukraine

The influence of possible presence of Co2+ ion pairs in a bulk Zn1-xCoxO mixed crystal on the low-frequency part of the Raman spectrum is discussed. Two effects can be taken into account in the theoretical considerations when analyzing the energy level scheme corresponding to Co ions. The first is a local lattice deformation in the vicinity of Co2+ ion due to a presence of the second ion, smaller than the host ZnO lattice cation. Such deformation creates a trigonal field, which can only slightly modify the energy levels of v ion. The second effect, which results from an antiferromagnetic superexchange interaction between two Co2+ ions is responsible for a new set of energy levels. The Raman data taken at low temperature on the sample corresponding to the composition x = 0.016 demonstrated the presence of two structures at about 6 cm(-1) and 13 cm(-1). These structures may be interpreted as electronic transitions between the ground state and the first excited state of a single Co2+ ion in the substitution site of ZnO lattice and as a similar transition for Co2+ ion pair, respectively.

The purpose of this study was to investigate the magnetotransport properties of the Ge(0.743)Pb(0.183)Mn(0.074)Te mixed crystal. The results of magnetization measurements indicated that the compound is a spin-glass-like diluted magnetic semiconductor with critical temperature TSG = 97.5 K. Nanoclusters in the sample are observed. Both, matrix and clusters are magnetically active. Resistivity as a function of temperature has a minimum at 30 K. Below the minimum a variable-range hopping is observed, while above the minimum a metallic-like behavior occurs. The crystal has high hole concentration, p = 6.6E20 cm-3, temperature-independent. Magnetoresistance amplitude changes from -0.78 to 1.18% with increase of temperature. In the magnetotransport measurements we observed the anomalous Hall effect (AHE) with hysteresis loops. Calculated AHE coefficient, RS = 2.0E6 m3/C, is temperature independent. The analysis indicates the extrinsic skew scattering mechanism to be the main physical mechanism responsible for AHE in Ge(0.743)Pb(0.183)Mn(0.074)Te alloy., Comment: 4 pages, 3 figures

We consider theoretically the topological contribution to the anomalous Hall effect in narrow-gap IV–VI magnetic semiconductors in which the relativistic terms are relatively large and determine both the non-parabolicity of the energy spectrum and strong spin–orbit interaction. We use the relativistic Dirac model and linear response theory to calculate this contribution. Experimental data on the anomalous Hall effect in these compounds are also presented and discussed.

We present the experimental evidence for the presence of spinodal decomposition of the magnetic ions in the Ge/1-x-y/Cr/x/Eu/y/Te samples with chemical composition varying in the range of 0.015 < x < 0.057 and 0.003 < y < 0.042. The ferromagnetic transition at temperatures 50 < T < 57 K was observed, independent of the chemical composition. The long-range carrier mediated itinerant magnetic interactions seem to be responsible for the observed ferromagnetic order. The magnetic irreversibility with coercive field H/C/ = 5?63 mT and the saturation magnetization M/S/ 2?6 emu/g are found to strongly depend on the chemical composition of the alloy., 4 pages, 4 figures

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.

Interesting possibilities of application gives co‐occurrence of ferroelectric and ferromagnetic properties. GeMnTe is known to possess such unique properties. Here, we report preliminary AC magnetic susceptibility and magnetization studies of GeMnTe co‐doped with another magnetic ion — Europium, aimed at investigating of Eu ions influence on the magnetic properties of the resulting quaternary compound. We found that the Curie temperature of GeMnEuTe substantially (about 3 times) exceeds the values of TC reported in GeMnTe crystals and layers with similar Mn composition, equal ∼40 K. The origin of this substantial Curie temperature enlargement is not fully explained yet. However, the spin‐echo resonance data may suggest that the Mn2+ ions system is in a mixed valence state and that an additional channel of interaction between magnetic ions is open.

Magnetic and transport properties of ferromagnetic semiconductors (FMSs) near the ferromagnetic-paramagnetic phase transition were studied in two classes of FMSs: in the III–V-based In1−xMnxSb and Ga1−xMnxAs epitaxial films and in IV–VI-based Sn1−xMnxTe and Sn1−x−yMnxEryTe alloys in bulk crystal form. Magnetoresistance data for both FMS classes are in excellent agreement with the theory of Majumdar and Littlewood, indicating that near the Curie temperature, magnetic fluctuations play a key role as scattering centers. These results also show that the Majumdar–Littlewood model can be applied to magnetically very dilute systems.