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X-ray powder diffraction measurements and differential thermal analysis (DTA) were made on polycrystalline samples of the Cu 2 Cd 1−z Mn z GeSe 4 and Cu 2 Cd 1−z Fe z GeSe 4 alloy systems. The diffraction patterns were used to show the equilibrium conditions and to derive lattice parameter values. The effect of the annealing temperature and cooling rate to room temperature are discussed. For the Cu 2 Cd 1−z Fe z GeSe 4 system, only two single solid phase fields, the tetragonal stannite ␣ and the wurtz-stannite ␦ structures were found to occur in the diagram. For the Cu 2 Cd 1−z Mn z GeSe 4 system, in addition to the tetragonal stannite ␣ and the wurtz-stannite ␦ phases, MnSe was found to exist in the diagram. The DTA experiments showed that the cooling curves for both systems exhibited effects of undercooling.

Measurements of magnetic susceptibility χ as a function of temperature T and of magnetization M as a function of applied magnetic field B at a number of fixed temperatures were made on polycrystalline samples of Cu2Cd0.25Fe0.75GeSe4 and Cu2FeGeTe4. The χ vs T data show that the Cu2Cd0.25Fe0.75GeSe4 alloy is antiferromagnetic with a Néel temperature TN of about 12K, while the Cu2FeGeTe4 has a magnetic transition at about 160K. The M vs B results obtained on Cu2Cd0.25Fe0.75GeSe4 indicated that bound magnetic polarons (BMPs), associated with holes bound to acceptors, occur in the paramagnetic and antiferromagnetic phases, and that the effects from BMPs disappear at approximately 50K. In the case of the Cu2FeGeTe4 compound, effects due to the presence of BMPs were not observed in the material. For the Cu2Cd0.25Fe0.75GeSe4, the M vs B curves were well fitted by a Langevin-type of equation and the variation of the fitting parameters determined as a function of temperature. It was found that, in the temperature range between 15 and 50K, the number of BMPs remained practically constant having a mean value of 3.8×1018∕cm3. The analysis gave a value of 305μB for the average magnetic moment of a BMP, corresponding to 61 Fe atoms. Using a simple spherical model, this gives the BMP radius of about 14Å; this value is close to the expected radius of the hole orbit, of the order of 10Å.

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.

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