[en] The magnetic phase diagram of MnGa₂Se₄ was obtained by means of low magnetic field susceptibility in the temperature range from 2 to 300 K and high magnetic field magnetization measurements at several temperatures between 2 and 150 K, by using a MPMS-5 magnetometer and pulsed magnetic fields method, respectively. The obtained results show that the phase diagram is consistent with the uniaxial antiferromagnetic material when the field is applied parallel to the easy axis

[en] Measurements of low field static magnetic susceptibility and of magnetization with pulsed magnetic fields up to 32 T have been made as a function of temperature on polycrystalline samples of the compound Ag₂FeGeSe₄ (AFG) which has an orthorhombic wurtz-stannite structure. The resulting data have been used to give information on the magnetic spin-flop (SF) and magnetic saturation transitions. It was found that AFG has a Neel temperature of 240 K, shows mainly antiferromagnetic behaviour with a very weak superimposed ferromagnetic component down to 60 K. At 60 K, a transition occurs resulting in an appreciably larger ferromagnetic effect below the transition. The ferromagnetic component is attributed to spin canting, with the transition at 60 K due to a discontinuous change in the canting angle. Thus, the SF and saturation fields show very different behaviour below and above 60 K. Details of the magnetic B-T phase diagrams were determined for the two phases and the results compared with the predictions of theoretical uniaxial models

[en] Optical absorption measurements were made in the temperature range 9-300 K on the chalcopyrite semiconductor compound AgGaSe₂ and the optical energy gap E_G determined as a function of temperature T. In order to obtain the values of E_G 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 E_G 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.

[en] A comparative study of the Raman spectra of Cu₂B^IIC^IVS₄^VI and Cu₂B^IIC^IVSe₄^VI(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 C^IV cations remaining at rest. The shift in the frequency of these two lines of about 150 cm⁻¹ to lower energies observed in Cu₂B^IIC^IVSe₄^VI compounds as compared to those in Cu₂B^IIC^IVS₄^VI 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 Cu₂B^IIC^IVX₄^VI 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

[en] Polycrystalline samples of Cu₃TaIn₃Se₇ and CuTa₂InTe₄ were synthesized by the usual melt and anneal technique. X-ray powder diffraction showed a single phase behavior for both samples with tetragonal symmetry and unit cell parameter values a=5.794±0.002 A, c=11.66±0.01 A, c/a=2.01, V=391±1 A³ and a=6.193±0.001 A, c=12.400 ±0.002A, c/a=2.00, V=475±1 A³, respectively. Differential thermal analysis (DTA) measurements suggested a complicated behavior near the melting point with several thermal transitions observed in the heating and cooling runs. From the shape of the DTA peaks it was deduced that the melting is incongruent for both materials. Magnetic susceptibility measurements (zero-field cooling and field cooling) indicated an antiferromagnetic character with transition temperatures of T=70 K (Cu₃TaIn₃Se₇) and 42 K (CuTa₂InTe₄). A spin-glass transition was observed in Cu₃TaIn₃Se₇ with T_f∼50 K. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] Measurements of X-ray diffraction, differential thermal analysis (DTA) and of magnetic susceptibility χ, in the temperature range from 2 to 300 K, were carried out on polycrystalline samples of the Zn_1-zMn_zIn₂Te₄ alloy system. The X-ray diffraction patterns were used to check the equilibrium conditions and to estimate crystalline parameter values. The DTA transition temperature values were plotted as a function of alloy composition z. The 1/χ vs T curves indicated that samples in the α₁I4-bar range (0< z<0.4) were antiferromagnetic showing ideal Curie-Weiss behavior, but for all samples in the γI4-bar 2m range (0.4< z<1) the behavior was spin-glass. The values of the Curie-Weiss temperature θ determined from all of the 1/χ vs T curves were used to give the type ordering and the degree of order of the Mn atoms in the several solid fields which occur in the present T(z) diagram.

[en] Measurements of magnetic susceptibility χ have been made as a function of temperature in the range 2-300 K on polycrystalline samples of the Cu₂Cd_1-zMn_zGeSe₄ and Cu₂Cd_1-zFe_zGeSe₄ alloy systems. Values of T_N, the antiferromagnetic Neel 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 Cu₂Cd_1-zFe_zGeSe₄ 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 T_N and θ data

[en] X-ray powder diffraction measurements, at room temperature, and magnetic susceptibility χ measurements, in the temperature range from 2 to 300 K, 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 Neel temperature of 30 K, 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 T_C of 149.9 and 301 K, 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 B_C and the remanent magnetization M_r were found to vary nonlinearly with the temperature T

[en] X-ray powder diffraction and differential thermal analysis (DTA) measurements were made on polycrystalline samples of the Cu₂Zn_1-zFe_zGeSe₄ 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 α structure (I4-bar2m) occurs across the whole composition range. The DTA thermograms were used to construct the phase diagram of the Cu₂Zn_1-zFe_zGeSe₄ alloy system. It was confirmed that the Cu₂ZnGeSe₄ compound melts incongruently. It was observed that undercooling effects occur for samples with z > 0.9

[en] Highlights: • The samples were annealed at 500 °C for 1 month. • Samples in the ranges 0 < z < 0.375 had the tetragonal stannite α structure (I4"¯2m). • For 0.725 < z ⩽ 1 the wurtz–stannite δ structure (Pmn2_1). • Undercooling effects occur for samples in the range 0.725 < z < 0.925. - Abstract: The T(z) phase diagram of the Cu_2Zn_1_−_zMn_zGeSe_4 alloy system is obtained from X-ray diffraction and differential thermal analysis DTA. At room temperature, the X-ray diffraction data showed that samples in the ranges 0 < z < 0.375 had the tetragonal stannite α structure (I4"¯2m), while for 0.725 < z ⩽ 1 the wurtz–stannite δ structure (Pmn2_1). The α and δ fields are separated by a relative wide three-phase field (α + δ + MnSe_2). The DTA thermograms were used to construct the phase diagram of the Cu_2Zn_1_−_zMn_zGeSe_4 alloy system. It was confirmed that the Cu_2ZnGeSe_4 and Cu_2MnGeSe_4 compounds melt incongruently. It was observed that undercooling effects occur for samples in the range 0.725 < z < 0.925