Measurements of magnetic susceptibility ? as a function of temperature in the range 2-300 K on polycrystalline samples of Cu2Cd1-zMnzSnSe4 magnetic semiconductor alloy system are reported. The Curie constant C increase linearly with z. The Curie-Weiss temperature ? and Neel temperature TN increase linearly with z due to a partial order change to total disorder of the Mn+2 ions in the system. In a first approximation, it can be considered that this system has typical spin glass behavior (spin glass system), which means that ions Mn+2 are somewhat disorderly way cationic network of material.

The structural study and phase diagram of the alloy system Cu2Zn1-zMnzSnSe4 are reported. Polycrystalline samples were synthesized using the direct fusion and annealing technique from the constituent elements. X-ray diffraction analysis indicates that system crystallizes in the tetragonal stannite structure with a possible I4 2m space group. From differential thermic analysis (DTA) experiment the phase diagram was constructed for alloy system, which suggests that the region between 600 and 700 °C is biphasic coexisting stannite and wurtz-stannite phases (+). The peritectic decomposition of the system   (L+ZnSe) in the region between z = 0 and z  0.80 occurs at  800 oC, for z > 0.80 the peritectic temperature decreases to 700 oC with z = 1.0. The transition of liquid L to (L+ZnSe) is given by the boundary line between 1075 oC with z = 0 and 770 oC with z  0.80. The region of the diagram below 600 oC corresponds to the appearance of the tetragonal stannite phase, as it indicated by the X-ray diffraction study at room temperature.

The temperature dependence of the Raman scattering by phonons performed in bulk polycrystalline Cu2FeSnS4, that crystallizes with tetragonal symmetry in space group P, was measured between 10 and 300 K. The most important decay channel involves the three‐phonon process with two phonons of the same branch, including combinations of optical phonons with equal or different frequencies. Additionally, coupling of an optical mode to two phonons of different branches is observed. The strong A‐symmetry mode at 325 cm−1 decays into two optical phonons of the same frequencies 1 = 2 ≈ 162 cm−1. To explain the change of Raman shift with temperature it is necessary to take into account the contribution of thermal expansion contribution. We have observed a soft mode in the Raman spectra which accounts for the antiferromagnetic phase transition that happens in this material at a Néel temperature of about 40 K. The full width at half maximum of this A‐symmetry mode, extrapolated to zero temperature, is of about 2.6 cm−1, when the contribution of intrinsic defect scattering, which is of about 3. cm−1, is included in the calculation.

En este trabajo se reportan las medidas de susceptibilidad magnetica c en funcion de la temperatura en el rango de 2-300 K de muestras policristalinas del sistema de aleaciones semiconductor magnetico Cu 2 Cd 1 − z Mn z SnSe 4 . La constante de Curie C aumenta linealmente con la concentracion z. La temperatura de Curie-Weiss q y la temperatura de Neel T N aumentan linealmente con la concentracion z, debido a un cambio de orden parcial a desorden total de los atomos de Mn 2+ en el sistema. En una primera aproximacion, se puede considerar que el sistema de aleaciones tiene un comportamiento tipico de vidrio de espin, lo que implica que los iones de Mn 2+ se encuentran de alguna manera desordenados en la red cationica del material. Measurements of magnetic susceptibility c as a function of temperature in the range 2-300 K on polycrystalline samples of Cu 2 Cd 1 − z Mn z SnSe 4 magnetic semiconductor alloy system are reported. The Curie constant C increase linearly with z. The Curie-Weiss temperature θ and Neel temperature T N increase linearly with z due to a partial order change to total disorder of the Mn +2 ions in the system. In a first approximation, it can be considered that this system has typical spin glass behavior (spin glass system), which means that ions Mn +2 are somewhat disorderly way cationic network of material.

Measurements of magnetic susceptibility χ as a function of temperature (from 2 to 300 K) were made on polycrystalline samples of the compounds Cu2MnSiS4, Cu2MnGeS4, Cu2MnSnS4, Cu2FeSiS4 and Cu2FeGeS4. From the 1/ χ versus T curves, it was concluded that the samples were antiferromagnetic. These curves were also used to determine values of the Neel temperature TN and the Curie-Weiss temperature θ for each compound. When the values of TN and θ are plotted against its molecular weight W, it was found that the compounds containing Mn lie on the same straight line, while those with Fe lie on a different one. For each compound, an analysis was carried out in terms of the simple mean-field theory and using the virtual transition model of Geertsma et al. for exchange interaction, and values of exchange interaction parameters were determined from the measured TN and θ data.

We show that a phenomenological model based on sublattice magnetization describes the temperature and field dependent magnetism in the Ag2FeGeSe4 semiconductor compound with wurtz-stannite-type structure. The model successfully finds the antiferromagnetic (AF), spin flop (SF) and paramagnetic (P) phases for all magnetization curves below the Neel temperature. The Langevin classical function instead of the Brillouin one is used in the analysis of the phase transitions to take into account the randomness of the magnetic moments given the polycrystalline nature of the samples. The critical-fields and the thermal broadening of the phase transitions were also found. The model was tested in the Ba3Cu3In4O12 and Ba3Cu3Sc4O12 compounds, and was successfully identified AF, SF and P phases in these materials.

Measurements of magnetic susceptibility χ as a function of temperature (from 2 to 300 K) were made on polycrystalline samples of the compounds Cu 2 MnSiS 4 , Cu 2 MnGeS 4 , Cu 2 MnSnS 4 , Cu 2 FeSiS 4 and Cu 2 FeGeS 4 . From the 1/ χ versus T curves, it was concluded that the samples were antiferromagnetic. These curves were also used to determine values of the Neel temperature T N and the Curie-Weiss temperature θ for each compound. When the values of T N and θ are plotted against its molecular weight W, it was found that the compounds containing Mn lie on the same straight line, while those with Fe lie on a different one. For each compound, an analysis was carried out in terms of the simple mean-field theory and using the virtual transition model of Geertsma et al. for exchange interaction, and values of exchange interaction parameters were determined from the measured T N and θ data. Se realizaron medidas de la susceptibilidad magnetica χ en funcion de la temperatura (2 a 300K) sobre muestras policristalinas de los compuestos Cu 2 MnSiS 4 , Cu 2 MnGeS 4 , Cu 2 MnSnS 4 , Cu 2 FeSiS 4 y Cu 2 FeGeS 4 . De las curvas 1/ χ versus T, se concluye que las muestras fueron antiferromagneticas. Estas curvas fueron tambien usadas para determinar los valores de la temperaturas de Neel T N y de Curie-Weiss θ para cada uno de los compuestos. Cuando se grafican los valores de T N y θ en funcion del peso molecular W, se encuentra que tanto los compuestos que contienen Mn como Fe muestran una dependencia lineal, pero con diferentes pendientes. Para cada compuesto, fue llevado a cabo un analisis en terminos de la teoria de campo medio y el modelo de transicion virtual de Geertsma et al. para la interaccion de intercambio permitiendo la determinacion de los valores de los parametros de interaccion a partir de los valores medidos de T N y θ.

A comparative study of the Raman spectra of Cu2BIICIVS4VI and Cu2BIICIVSe4VI(where B = Mn or Fe) magnetic quaternary semiconductor compounds with stannite-type structure (I4¯2m) has been done. Most of the fourteen Raman lines expected for these materials were observed in the spectra. The two strongest lines observed have been assigned to the IR inactive A11 and A12 stannite modes that originated from the motion of the S or Se anion around the Cu and CIV cations remaining at rest. The shift in the frequency of these two lines of about 150 cm−1 to lower energies observed in Cu2BIICIVSe4VI compounds as compared to those in Cu2BIICIVS4VI ones, can then be explained as due to the anion mass effect. Based on the fact that values of these frequencies depend mainly on anion mass and bond-stretching forces between nearest-neighbor atoms, the vibrational frequencies v¯(A12) and v¯(A12) of both modes for several Cu2BIICIVX4VI stannite compounds (where X = S, Se, or Te) very close to the experimental data reported for these materials were calculated from a simple model that relates these stretching forces to the anion-cation bond-distances.

X-ray powder diffraction and differential thermal analysis (DTA) measurements were made on polycrystalline samples of the Cu2Zn1-zFezGeSe4 alloy system. The diffraction patterns were used to show the equilibrium conditions and to estimate crystalline parameter values. It was found that, at room temperature, a single phase solid solution with the tetragonal stannite alpha structure (1 (4) over bar 2m) occurs across the whole composition range. The DTA thermograms were used to construct the phase diagram of the Cu2Zn1-zFezGeSe4 alloy system. It was confirmed that the Cu2ZnGeSe4 compound melts incongruently. It was observed that undercooling effects occur for samples with z > 0.9. (C) 2007 Elsevier B.V. All rights reserved.

The temperature dependencies of DC magnetic susceptibilities, χ(T), of CuFeInTe3 and CuFeGaTe3 alloys were measured in a SQUID apparatus using the protocol of field cooling (FC) and zero FC (ZFC). The FC curves of both samples reflect a weak ferromagnetic (or ferrimagnetic) behavior with a nearly constant value of χ(T) in the measured temperature range (2–300 K) indicating that the critical temperatures (Tc) are >300 K. The ZFC curves diverges from FC, showing irreversibility temperatures (Tirr) of ∼250 K for CuFeInTe3 and >300 K for CuFeGaTe3, suggesting that we are dealing with cluster‐glass systems in a superparamagnetic state.

In an attempt to resolve the crystal structure and the corresponding space group of the magnetic semiconductor Cu2FeSnS4, samples of this compound were studied by X-ray diffraction, differential thermal analysis, Raman scattering and magnetic susceptibility. It was found that at room temperature this compound prepared by a careful crystal growth process, including annealing to equilibrium at a suitable temperature followed by slow cooling of the samples to 300 K, crystallizes in a tetragonal structure with space group P4̄.

Magnetic susceptibility chi measurements in the range from 2 to 300 K were carried out on samples of the Cu2FeSnSe4 and Cu2MnSnSe4 compounds. It was found that Cu2FeSnSe4 was antiferromagnetic showing ideal Curie-Weiss behavior with a Neel temperature T-N of about 19 K and Curie-Weiss temperature 0 = -200 K, while for Cu2MnSnSe4 the behavior was spin-glass with a freezing temperature T-f of about 22K and Curie-Weiss temperature 0 = -25 K. The spin-glass order parameter q(T), determined from the susceptibility data, was found to be in agreement with the prediction of conventional spin-glass theory. (C) 2010 Elsevier Ltd. All rights reserved.

In order to resolve the crystal structure and the corresponding space group of the tetrahedrally coordinated II–III2–V I4 defective semiconductor ZnGa2Se4, a study of the magnetic susceptibility of the alloy system Zn1−zMnzGa2Se4 is performed. The analysis of the Curie–Weiss temperature confirms, consistently with the phase diagram previously reported, that the room temperature crystal structure of the alloy system Zn1−zMnzGa2Se4 in all the composition ranges (0≤z≤1) is of defect chalcopyrite type with space group I4̄ while samples obtained at temperatures higher than about 500°C, which are rapidly cooled to room temperature, crystallizes in the partially disordered stannite-type structure I4̄2m. Hence, a careful process of crystal growth of this system, including a study of the phase diagram, annealing at adequate temperature, and slow cooling of the samples is necessary in order to obtain specimens in the ordered phase.

Measurements of magnetic susceptibility χ have been made as a function of temperature in the range 2–300K on polycrystalline samples of the Cu2Cd1−zMnzGeSe4 and Cu2Cd1−zFezGeSe4 alloy systems. Values of TN, the antiferromagnetic Néel temperature, have been obtained from the cusp in the χ vs. T curves. Values of the Curie–Weiss temperature θ and the Curie constant C have been determined from the 1/χ vs. T results. It has been found that, for each system, the orbital moment L is quenched. In the case of the Cu2Cd1−zFezGeSe4 system, an analysis was carried out in terms of a simple mean field theory, and values of exchange interaction parameters were determined from the measured TN and θ data.

Optical absorption measurements were made in the temperature range 9–300K on the chalcopyrite semiconductor compound AgGaSe2 and the optical energy gap EG determined as a function of temperature T. In order to obtain the values of EG as a function of T, the Elliot-Toyozawa model [R.J. Elliot, J. Phys. Rev. 108 (1957) 1384; D.D. Sell, P. Lawaets, Phys. Rev. Lett. 26 (1971) 311] was employed to perform the analysis of the optical absorption spectra. The resulting EG vs. T curve was fitted to a semi-empirical model that takes into account both the thermal expansion and the electron–phonon interaction contributions. The results have been used to estimate values of the deformation potentials of the valence and conduction bands of the compound.

X-ray powder diffraction measurements and differential thermal analysis (DTA) were made on polycrystalline samples of the Cu2Cd1−zMnzSnSe4 and Cu2Cd1−zFezSnSe4 alloy systems. The diffraction patterns were used to show the equilibrium conditions and to derive lattice parameter values. For Cu2Cd0.8Fe0.2SnSe4 as well as for Cu2Cd0.2Fe0.8SnSe4 the crystal structures were refined using the Rietveld method. It was found that the internal distortion parameter σ decreases as Cd is replaced by either Mn and/or Fe. For the Cu2Cd1−zMnzSnSe4 and Cu2Cd1−zFezSnSe4 alloy systems, only two single solid phase fields, the tetragonal stannite α (I4¯2m) and the wurtz–stannite δ (Pmn21) structures were found to occur in the diagram. In addition to the tetragonal stannite α phase extra X-ray diffraction lines due to MnSe and/or FeSe2 were observed for as grown samples in the range 0.7<z<1.0. However, it was found that the amount of the extra phase decreased for the compressed samples.

X-ray powder diffraction measurements, at room temperature, and magnetic susceptibility χ measurements, in the temperature range from 2 to 300K, were made on polycrystalline samples of Mn2GeTe4, Fe2GeTe4 and Fe2SnSe4 compounds, which would be useful for spintronic device production. Magnetization M measurements at various temperatures were carried out on the Fe-compounds. From the analysis of the X-ray diffraction patterns, it was found that the Mn2GeTe4, Fe2GeTe4 and Fe2SnSe4 have orthorhombic structure, possibly an olivine structure-type (SG: Pnma No. 62, z=4). It was found that Mn2GeTe4 has a Néel temperature of 30K, shows mainly antiferromagnetic behavior with a weak superimposed ferromagnetic component which is attributed to spin canting. The resulting susceptibility χ versus T curves for Fe2GeTe4 and Fe2SnSe4 were found to have, in each case, a form which is typical of a ferromagnetic material with Curie temperatures TC of 149.9 and 301K, respectively. The critical exponent β for the Fe-compounds were found to be very similar and close to the expected value for a ferromagnetic material, in the range 0.33–0.39. The values of the coercive field BC and the remanent magnetization Mr were found to vary nonlinearly with the temperature T.