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The magnetic susceptibility of Pb1-xCexA (A=S, Se and Te) crystals with Ce3+ concentrations 0.006≤x≤0.036 was investigated in the temperature range from 2 K to 300 K. The magnetic susceptibility data was found to be consistent with a 2F5/2 lowest manifold for Ce3+ ions with a crystal-field splitting Δ=E(Γ8)−E(Γ7) of about 340 K, 440 K and 540 K for Pb1-xCexTe, Pb1-xCexSe, and Pb1-xCexS, respectively. For all the three compounds the doublet Γ7 lies below the Γ8 quadruplet which confirms the substitution of Pb2+ by Ce3+ ions in the host crystals. The observed values for the crystal-field splitting are in good agreement with the calculated ones based on the point-charge model. Moreover, the effective Lande factors were determined by X-band (∼9.5 GHz), electron paramagnetic measurements (EPR) to be g=1.333, 1.364, and 1.402 for Ce ions in PbA, A = S, Se and Te, respectively. The small difference with the predicted Lande factor g of 10/7 for the Γ7 (J=5/2) ground state was attributed to crystal-field admixture.

The magnetic susceptibility of Pb1-xCexX (X = S, Se and Te) crystals with several Cerium concentrations ranging from x = 0.006 to 0.036 has been measured between 2 K and 300 K. The experimental susceptibility curves were found to be consistent with a 2F5/2 lowest manifold for Ce3+ ions; the cubic crystal-field splitting values of 2F5/2 were estimated to be about 340 K, 440 K and 540 K for Pb1-xCexTe, Pb1-xCexSe, and Pb1-xCexS, respectively. For all the studied samples, it was found that the 7 doublet lies below the 8 quadruplet. These results confirm that Ce3+ ions substitute Pb2+ in the host crystals. Furthermore, the effective Landé factors were determined by X-band (~9.5 GHz) Electron Paramagnetic Measurements (EPR) to be g = 1.333, 1.364, and 1.402 for Ce ions in PbX, X = S, Se, and Te, respectively.

Cd0.2Zn0.8Te monocrystals with the sizes of about 15 mm have been produced by self-selecting vapour growth (SSVG). High degree of structural perfection of monocrystalline Cd0.2Zn0.8Te was achieved. Excellent compositional uniformity was observed as well. To our knowledge, no comparable results are reported for this solid solution. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

36th International School on the Physics of Semiconducting Compounds, Jaszowiec, POLAND, JUN 09-15, 2007; International audience; Low-temperature Raman spectra of a bulk mixed crystal Zn1-xCoxO (x = 0.016) are shown and analyzed. Besides the common modes of the ZnO host lattice, electronic transitions related to the presence of Co2+ ions at the Zn sites are observed. In spite of the low Co concentration the presence of collective excitations corresponding to Co and CoO precipitates is also revealed.

The Mn/ZnO(0001) system was investigated by synchrotron radiation photoemission. The Mn/ZnO interface with 4 ML of manganese deposited onto the ZnO surface was annealed up to 500◦C. No Mn capping layer was found at the surface after annealing as was confirmed by scanning Auger spectroscopy experiment. We used a resonant photoemission to extract the Mn3d partial density of states in photoemission spectra. The Mn3d states contribute to the electronic structure of the system within 10 eV of the Fermi level. They show three features: a main peak at 3.8–4.5 eV, a valence structure at the top of the valence band (1–3 eV), and a broad satellite situated between 5.5 and 9 eV below EF. The satellite/main branching ratio was determined to be 0.43, which is a fingerprint of strong hybridization between the Mn3d electrons and the valence band of the crystal. The hybridization effect in Zn1−xMnxO surface alloy is comparable to Zn1−xMnxS and much higher than in Zn1−xMnxSe, Zn1−xMnxTe, and Ga1−xMnxAs semimagnetic compounds.

We report on Raman scattering spectra of two systems ZnO:Ti and ZnO:Mn. The spectra have been measured vs. temperature, excitation laser light wavelength, and light polarization. A new, strongly temperature dependent Raman peak has been found in the ZnO:Ti system as a satellite of the E2 (high) phonon peak. The peak is interpreted as an A1 electronic transition strongly coupled to the phonon spectrum of the crystal. Several new phonon bands are found in both materials. The new peaks are interpreted either as the disorder activated phonon modes or local vibrations of Ti and Mn related complexes in ZnO. © 2005 Elsevier Ltd. All rights reserved.

Measurements of transport and non-linear optical (NLO) properties of the new, synthesized semiconductor Pb0.9835Pr0.0165Te in the vicinity of low-temperature metal–semiconductor phase transformations were performed. A correlation between the temperature behaviour of transport properties near the phase transition and NLO susceptibilities of second- and third-order was observed. FTIR spectra show the substantial role played by the Pr3+ localized levels in the observed anomalies.Among the transport properties, the resistivity, Seebeck coefficient and specific heat were measured. The presence of the minimum at about in the temperature dependence of the resistivity ρ(T) is due to the metal–semiconductor transition in Pb1−xPrxTe and the low-temperature upturn observed in the resistivity is well fitted by the Mott law. Substitution of PbTe by other rare earths shows the crucial role played by Pr in the observed dependences.Experimental temperature measurements using photo-induced NLO (pumped by a UV-laser as well as by second harmonics of the YAG–Nd lasers) and a probing YAG–Nd (at λ = 1.06 µm) laser, show the existence of two maxima in the photo-induced second harmonic generation (PISHG) at temperatures 17 and 30 K, the behaviours of which substantially depend on the wavelength of the pump beam. At the same time the third-order two-photon absorption possesses maxima near 50 K, i.e. at about . Such discrepancies in the positions of the temperature maxima are caused by the difference in contributions of the photo-induced anharmonic phonons near the surfaces PISHG and the bulk. Varying the penetration depth of the photo-inducing light one can operate with the output NLO properties.

Sn 1− x Mn x Se 2 crystals have been grown by a modified Bridgman method aiming to form a new semimagnetic semiconductor whose particularity will be to have a layered CdI 2 -type crystal structure. This paper reports the first detailed structural and photoemission study of this new material. X-ray diffraction analysis performed on two different samples showed that only one had the expected lattice symmetry, the other one being a mixture of SnSe and α-MnSe phases. Although the preparation method of these specimen was the same they differed by the manganese quantity inserted to substitute tin in the SnSe 2 lattice. This study also reveals that Mn-solubility into this lattice is not high. Photoelectron spectroscopy using X-ray and synchrotron radiation were also carried on. As it was expected, chemical states of tin and selenium in layered Sn 1− x Mn x Se 2 are Sn 4+ and Se 2− , respectively. Manganese is present as Mn 2+ ion, like it is the case in II 1 −x Mn x VI materials. Investigations of layered Sn 1− x Mn x Se 2 valence band revealed that the Mn 3d density of states is constituted of localized states at 3.5 eV of binding energy with delocalized states at lower and higher energy. Differences in Mn 3d density of states have been observed with respect to a biphased Sn 1− x Mn x Se 2 compound.

We report on a comprehensive study of the Sm/GaN(0 0 0 1 ) interface using synchrotron radiation photoemission. Spectra were taken after stepwise Sm deposition onto a clean GaN(0 0 0 1 ) surface at room temperature and after annealing. Based on the analysis of resonant photoemission spectra taken for hν=136 eV (divalent samarium resonance) and hν=141 eV (trivalent samarium resonance) we find that both divalent and trivalent samarium states are present in the GaN–Sm interface layer after each step of deposition. The average valence of the system increases from 2.57 for a coverage of 0.6 A to 2.73 for 3.2 A. Above this coverage the average valence drops and reaches a final value of 2.63 for a coverage of 10 A. The Ga3d core level evolution confirms that two valence Sm states are present in the interface region. A large chemical shift of the Ga3d core level after samarium deposition and a moderate decrease in the Ga3d attenuation curve indicate that a reactive interface is created when Sm atoms are deposited on the GaN(0 0 0 1 ) surface. Annealing of the Sm/GaN system to 500 °C induces a valence change from Sm2+ to Sm3+ and promotes diffusion of Sm from the interface into the bulk.

We analyze optical and magnetic properties of ZnO crystals grown by chemical transport method using chlorine as the transporting agent. Doping during the growth process with several transition metal ions is applied in an attempt to create observable magnetic ordering in the crystals. Our magnetic resonance and magnetization measurements indicate a paramagnetic phase in all obtained crystals. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

CdSxTe1-x has been used as a model substance to investigate crystal growth from the vapour, twinning phenomena and the electrical properties of grain boundaries. A self-selecting vapour growth method produced solid solutions of CdSxTe1-x (x?0.067) with compositional uniformity of

Origin of a fast component of the photoluminescence (PL) decay of Mn 2+ intra-shell 4T1 ? 6A 1 transition in bulk and quantum dot structures is discussed based on the results of PL, PL kinetics and ...

A study of the effect of annealing on the magnetic properties of single crystals Sn 1− x Eu x Te is reported. The width of the electron paramagnetic resonance line of the crystal is found to decrease upon annealing but its g -value of 1.991 is nearly unaffected. Magnetization results indicate that the pair exchange interaction is weakly antiferromagnetic with a value of −0.67 K for the non-annealed sample and −0.29 K after annealed sample. Susceptibility measurements performed as a function of temperature also indicate the presence of EuTe clusters in the as-grown Sn 1− x Eu x Te crystals. Therefore it was deduced that the Eu 2+ ions tend to form clusters, particularly pairs, in the as-grown crystal and these clusters disappear after annealing, as the Eu 2+ ions occupy isolated sites in the SnTe host lattice.

A lamellar semimagnetic semiconductor, Sn 1− x Mn x Se 2 , has been investigated by photoemission, both in the UV and X-ray photoenergy ranges. The partial Mn 3d DOS has been determined from resonant photoemission spectra; the valence of the several constituting atomic species was ascertained from XPS results.

The electronic structure of the Hg-chalcogenides HgTe and HgSe was studied by means of high resolved photoemission along the ΓΣ K -direction with the aim of investigating prototype materials for the inverted band structure model in detail. The samples were prepared by cleavage of the non polar (110)-surface plane to minimize the effects of surface charges. Assuming free electron parabola for the final states and considering reciprocal umklapp vectors the bulk band structure of the complete valence band was determined. This enabled a comparison to a state of the art–theoretical band structure calculation and to older experimental results obtained with different methods. In the case of HgTe with large spin–orbit splitting also the individual Γ 7 , Γ 6 , and Γ 8 -bands could be resolved at the valence band maximum, confirming the model of the inverted band structure directly. An attempt was made to apply this direct method also to HgSe.

The magnetization of Sn1-x Eux Te, with x = 0.011 and 0.042, was measured at 20 mK in magnetic fields up to 90 kOe. Magnetization steps (MSTs) from pairs and triplets were observed. The MSTs give J /kB = -0.311±0.006 K for the dominant Eu-Eu exchange constant. Comparisons of the magnetization curves with numerical simulations indicate that, instead of being distributed randomly, the Eu ions tend to bunch together. A phenomenological approach which uses the concept of a local Eu concentration xL is quite successful in describing the data for these two samples.

Resonant photoemission spectroscopy has been applied to study the group of Pb 1− x RE x B VI (RE=Eu, Gd; B=Te, Se, S) diluted magnetic semiconductors. Energy distribution curves, as well as constant-initial-state or constant-final-state photoemission spectra have been taken for photon energies near to the intra-ion Eu 4d→4f or Gd 4d→4f transitions. The Eu 4f and Gd 4f contributions to the electronic structures of the crystals have been determined by comparison of photoemission spectra taken on and off resonance. The localized character of the Eu(Gd) 4f 7 shell has been confirmed by the analysis of the shape of the corresponding spectral feature. The influence of the host crystal ionicity on the position of the RE 4f shells with respect to the valence band is discussed.

Monocrystals of sphalerite-type CdTe 1-x Se x were grown by self-selecting vapour growth SSVG in the horizontal configuration. As measured on a series of points of a (110) split plane, the rocking curve half-width was below 30 arcsec, while the lattice parameter measurements demonstrated the molar fraction x varying within 0.0024 (0.24 %) The values of x obtained from photoluminescence spectra taken from samples of different quality were in the ranges of 0.0034 (0.34 %) and 0.0047 (0.47 %). ()n the basis of the photoluminescence measurements, the maximum difference in x within the crystallised material was estimated to be 0.01 ( 1 %).

Electronic states of 4f samarium ions were investigated by photoemission spectroscopy in samarium-rich CdSmTe sample obtained by MBE. The photon energy of synchrotron radiation allowed to investigate Fano-type resonance and antiresonance. The energy distribution curve spectra were attributed to the Sm 4d-4f transition. The shape of the constant initial states spectra was compared with this one obtained for atomic samarium. PACS numbers: 73.20.At, 79.60.-i, 79.60.Bm

Single Zn 1− x Co x S crystals with x up to about 0.285 were grown by the chemical vapour transport method using iodine as the transporting agent. The obtained single crystal grains were typically of up to 3–6 mm in size. The crystal quality was studied with the help of high-resolution diffractometry. The FWHM of rocking curves was of the order of 40″. Lattice constants measured by both, the powder diffractometry and high-resolution diffractometry, are reported and compared with the literature data. The extrapolated lattice constant for hypothetical CoS compound of sphalerite-type structure is 5.343(1) A. The interatomic distances in Zn 1− x Co x S and in related Fe and Mn containing sulphides are briefly discussed.

Magnetization measurements were performed on five ${\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Eu}}_{x}\mathrm{S}$ samples, with $0.0092l~xl~0.059$. Two of the samples were measured at 20 mK in magnetic fields $\mathbf{H}$ up to 50 kOe parallel to the $[111]$ and $[100]$ directions. The other three samples were measured at 0.6 K in fields up to 180 kOe. The 20 mK data exhibit magnetization steps (MST's) arising from pairs. These MST's depend on the direction of H, so that anisotropic interactions must be included in the data analysis. The MST's lead to a value ${J/k}_{B}=\ensuremath{-}0.228\ifmmode\pm\else\textpm\fi{}0.007$ K for the dominant antiferromagnetic exchange constant. Computer simulations identify this $J$ as the nearest-neighbor exchange constant ${J}_{1}$, and show that the Eu distribution over the cation sites is random or very nearly random. The MST's from pairs exhibit a splitting when $\mathbf{H}$ is parallel to $[100]$. The splitting is tentatively attributed to exchange anisotropy, in which case the above value for $J$ refers to the average exchange constant $\overline{J}$. The 20 mK data for $\mathbf{H}||[100]$ also show a MST from isolated Eu ions. This MST occurs because such ``singles'' are subjected to a cubic crystal-field anisotropy.

Resonant photoemission spectroscopy was applied to the study contribution of Gd 4f states to the electronic structure ofSn 1− x Gd x Te. The energy distribution curves (EDC) were analyzed and the binding energy of Gd 4f shell was determined. The correspondence between the charge state of Gd ions and the binding energy of Gd 4f electrons was discussed.

ZnTe crystals have been grown by self-selecting vapour growth SSVG in a vertical, modified system, which reduces contact of the crystallised material with foreign materials to the minimum possible. Geometrical stability of the growth system is increased. The obtained crystals are of the sizes slightly below 10 mm and the rocking curve measurement results in the value of 36 arc sec. Distinct purification effect appears. The lattice constant of ZnTe is equal to 0.61036 nm.

Resonant photoemission spectra of Snι1-xGdxTe (x = 0.02 and 0.08) measured for the photon energy range 142 to 151 eV show the valence band density of states distribution and the Gd 4f derived maximum. The energy position of the J = 0 component of the Gd 4f maximum was determined and used as a measure of the Gd 4f shell binding energy. The electrostatic model of core level shifts was used to interpret the difference in the Gd 4f binding energies observed for x = 0.02 and x = 0.08.

The magnetization of ${\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Eu}}_{x}\mathrm{Te}$ samples with $x=0.019$, 0.026, and 0.060 was measured at 20 mK in fields up to 50 kOe, and at 0.6 K in fields up to 180 kOe. The 20 mK data show the magnetization steps (MST's) arising from pairs and from triplets. The pair MST's are used to obtain the dominant Eu-Eu antiferromagnetic exchange constant, ${J/k}_{B}=\ensuremath{-}0.264\ifmmode\pm\else\textpm\fi{}0.018$ K. The exchange constant for triplets is the same. Comparison of the magnetization curves with theoretical simulations indicates that the Eu ions are not randomly distributed over all the cation sites. The deviation from a random distribution is much smaller if $J$ is assumed to be the nearest-neighbor exchange constant ${J}_{1}$ rather than the next-nearest-neighbor exchange constant ${J}_{2}$. On this basis, $J$ is tentatively identified as ${J}_{1}$. However, the possibility that ${J=J}_{2}$ cannot be excluded completely. To obtain agreement with the data, it must be assumed that the Eu ions tend to bunch together. Comparision with microprobe data indicates that the length scale for these concentration variations is smaller than a few $\ensuremath{\mu}$m. The theoretical simulations in the present work improve on those performed earlier by including clusters larger than three spins.

Electron paramagnetic resonance (EPR) experiments were performed on a ${\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Ce}}_{x}\mathrm{Se}$ crystal at liquid-helium temperatures and show very clearly that the doublet ${\ensuremath{\Gamma}}_{7}$ is the ground state for cerium ions. The cubic symmetry is shown and the effective Land\'e factor for the ${\mathrm{Ce}}^{3+}$ is determined to be $1.354\ifmmode\pm\else\textpm\fi{}0.003.$ An orbital reduction factor is introduced to explain the $g$ experimental value. High-field magnetization results are in good agreement with the EPR results. The nominal Ce composition in PbSe deduced from saturation of the magnetization, $x=0.0405\ifmmode\pm\else\textpm\fi{}0.0003,$ is very closed to the value determined by microprobe analysis $(x=0.04).$ At 1.5 K, an antiferromagnetic interaction between the nearest-neighbor cerium atoms is found, ${J}_{\mathrm{ex}}{/k}_{B}=\ensuremath{-}0.715\mathrm{K}.$ The low-field magnetic-susceptibility results show that the magnetic moment of cerium impurities is strongly temperature dependent, explained by the presence of the crystal-field effect and the Kondo effect.

X-ray photoelectron spectroscopy experiments on PbTe:Yb, PbS:Yb, PbTe, and PbS crystals have been performed using the monochromatized Al Kα radiation. The valence band spectrum of PbTe:Yb exhibits one set of peaks associated with divalent Yb initial states, but two sets associated with divalent and trivalent Yb are observed for PbS:Yb. The valency of Yb in PbTe:Yb is 2 (within an accuracy of the experiment) but in PbS:Yb the mixed valency of Yb is seen. These conclusions are confirmed by an analysis of Yb 4d spectra in PbTe:Yb and PbS:Yb crystals.

Electron paramagnetic resonance experiments were performed on ${\mathrm{Bi}}_{2(1\mathrm{\ensuremath{-}}\mathrm{x})}$${\mathrm{Gd}}_{2\mathrm{x}}$${\mathrm{Se}}_{3}$ and ${\mathrm{Pb}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Gd}}_{\mathrm{x}}$Se samples at room and liquid-helium temperatures. The ${\mathrm{Gd}}^{3+}$ sites are characterized by hexagonal and octahedral symmetries in ${\mathrm{Bi}}_{2(1\mathrm{\ensuremath{-}}\mathrm{x})}$${\mathrm{Gd}}_{2\mathrm{x}}$${\mathrm{Se}}_{3}$ and ${\mathrm{Pb}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Gd}}_{\mathrm{x}}$Se samples, respectively. The absolute signs of the spin-Hamiltonian parameters in ${\mathrm{Bi}}_{2(1\mathrm{\ensuremath{-}}\mathrm{x})}$${\mathrm{Gd}}_{2\mathrm{x}}$${\mathrm{Se}}_{3}$ were determined by comparing the intensities of the lines at room and liquid-helium temperatures: ${\mathrm{b}}_{2}^{0}$0,${\mathrm{nb}}_{4}^{0}$g0, and ${\mathrm{b}}_{6}^{0}$0. The |${\mathrm{b}}_{2}^{0}$| value in ${\mathrm{Bi}}_{2(1\mathrm{\ensuremath{-}}\mathrm{x})}$${\mathrm{Gd}}_{2\mathrm{x}}$${\mathrm{Se}}_{3}$ increased nonlinearly with decreasing temperature, becoming constant below 40 K. At the low temperature of 2.2 K, four hyperfine transitions due to the $^{155}\mathrm{Gd}$ isotope (I=3/2) were observed in ${\mathrm{Pb}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Gd}}_{\mathrm{x}}$Se, leading to the average value of the hyperfine-coupling constant of 2.55\ifmmode\pm\else\textpm\fi{}0.10 mT for the two $^{155}\mathrm{Gd}$ and $^{157}\mathrm{Gd}$ processing nonzero nuclear magnetic moments.

X-ray photoelectron spectroscopy experiments on SnTe crystals doped by Sm, Eu, and Yb were performed to determine the valency of these ions in the SnTe matrix. The analysis of the X-ray photoelectron spectroscopy valence-band spectra revealed that Eu and Yb are divalent while Sm is trivalent in SnTe. These conclusions were confirmed by studies of the binding energies of core levels (4d-levels of Yb and 3d-levels of Sm and Eu), which are not presented here.

Low and high field transport measurements have been performed on polycrystalline Pb1- x Yb x Te obtained by the Bridgman technique. Unannealed samples show semi-insulating conduction at low temperatures while annealed samples remain conducting in the whole temperature range. The results can be explained qualitatively by impurity levels lying within the fundamental gap. Using the magnetic field-dependent Hall technique, the concentration and mobility of carriers in different bands (or sub-bands) were extracted showing the coexistence of electrons and holes. The attribution of discrete carriers to each band is discussed.

Cd0.8Zn0.2Te monocrystals of about 12 mm in size were produced by self-selecting vapour growth (SSVG). The growth process leads to compositional uniformity of solid solutions due to small temperature differences acting in the growth space, and the influence of any foreign material in the phases of growing and cooling a crystal is avoided. The crystals were characterised by means of X-ray diffraction and low-temperature luminescence. Variation in the ZnTe molar fraction x below 0.002 (0.2%) and the “rocking curve” half-width around 30 arcsec were determined.

Detailed X-band (about 9.5 GHz) electron paramagnetic resonance (EPR) measurements were carried out at 295, 77 and 4.2 K on the Eu2+ ion in a Pb1-xEuxSe single crystal. The values of the spin-Hamiltonian parameters have been determined by a simultaneous fitting of all the EPR line positions recorded for various orientations of the external magnetic field in the [010] plane using a rigorous least-squares fitting procedure. The absolute sign of the zero-field splitting parameter b4 was determined to be positive from the relative intensities of lines at liquid-helium temperature (4.2 K). The excellent fit of the line positions to a cubic spin Hamiltonian confirms that the site symmetry for Eu2+ ions is, indeed, cubic in the Pb1-x,Eux,Se single crystal over the temperature range 4.2-295 K. The Dynosian shape of the EPR lines indicates the metallic nature of the Pb1-xEuxSe sample. The nearest-neighbour Eu2+-Eu2+ exchange interaction has been estimated to be 20.4 GHz (antiferromagnetic) from the exchange pair EPR spectrum at 4.2 K. The hyperfine interaction constants for the isotopes 151Eu and 153Eu have been estimated.

The magnetization M of Sn 1− x Eu x Te:EuTe, x ≦0.02, has been measured at 4.2 K in fields H up to 23 T. The average pair exchange interaction is antiferromagnetic with a value of about 0.5 K. For x -values greater than 0.014 the M vs. H curves show a definite knee with approximately linear behavior above and below the knee. The knee in the magnetization data and a cusp in the susceptibility at about 10 K are related to the presence of EuTe clusters in our samples.

The magnetization of Sn1 − xEuxTe, x < 0.02, containing EuTe inclusions, has been measured over a temperature range from 2 to 385 K at fields up to 5.4 T. The high-temperature susceptibility data indicate that the exchange between magnetic ions is smaller than that found in other AIVBVI chalcogenides containing Gd or Eu. A cusp in the temperature dependence of the susceptibility at about 10 K has been attributed to the presence of EuTe inclusions in our samples with highest Eu content. From magnetization measurements we conclude that the Eu ions, substituting for Sn, occur primarily as the magnetic ion Eu2+, although Hall measurements show that the addition of Eu tends to compensate the p-type SnTe host material.

Exchange interactions in diluted magnetic semiconductors Zn1−xCoxS, Zn1−xMnxSe and Cd1−xMnxSe were studied by electronic paramagnetic resonance in the far-infrared region in high magnetic field up to 40 T. For x ≈ 5%, transmission spectra exhibit very sharp satellite lines on both sides of the single magnetic ion resonance. These features are attributed to the exchange of coupled spin pairs. A calculation of the energy levels of the pairs, including Dzyaloshinskii-Moriya (DM) effects, and symmetrical exchange terms of the interaction tensor allows to extract from the measurements the values of anisotropic exchange constants: D e = 0.014 K and DDM = 0.18 K in Zn1−xMnxSe, D c = 0.009 K and DDM = 0.12 K in Cd1−xMnxSe, D e = 0.06 K in Zn1−xCoxS. The values of DM constants compare well with Larson et al.'s predictions. Moreover, in the case of cobalt, the occurrence of an absorption peak at half-field is well-interpreted by taking the symmetric anisotropic terms into account.

International audience; We report the results of a comprehensive study of the exchange interactions in Co-doped ZnO using inelastic neutron scattering, electron paramagnetic resonance, and magnetic property measurements. In particular, we observe an unprecedentedly strong spatial anisotropy of the two nearest-neighbor exchanges, J (1) = −25.6 ± 0.3 K and J (2) = −8.5 ± 0.4 K, along with the distant-neighbor J values of ferromagnetic sign. We argue that the superexchange mechanism alone cannot account for the obtained data and we suggest that an additional mechanism leading to a strong ferromagnetic spin coupling is responsible for these findings. We also discuss the origin of this ferromagnetic mechanism.

X-ray absorption experiments were performed at the Kedge of Co and Zn in Zn1-xCoxS and Zn1—mCoxSe compounds with x = 0.25, 0.16, 0.10, 0.05, 0.00 in the sulphides samples and x = 0.07, 0.02, 0.00 in the selenide ones. Analysis of the extended X-ray absorption fine structure oscillations using phase and amplitudes either from McKale code or from standard samples, gave the distance, number of atoms and the Debye-Waller factors for nearest neighbours. We found that the cation-anion distances Zn—S(Se) or Co—S(Se) are systematically shorter in ZnS than in ZnSe matrix, the Zn-anion distance is always larger than the Co-anion one without any significant Co content dependence. This allowed us to estimate the covalent radius of Co in the studied matrices to be 0.025 A smaller than the Zn covalent radius and stated that covalent radius of Co is independent of the type of surrounding atoms. In addition the Debye—Waller factors indicated a better ordering in ternary compounds than in the binary standard ones in agreement with rocking curve measurements. PACS numbers: 61.10.Lx, 87.64.Fb, 78.70.Dm