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X-ray powder diffraction measurements, at room temperature, and magnetic susceptibility c measurements, in the temperature range from 2 to 300 K, were made on polycrystalline samples of Cu 2 FeGeSe 4 and Cu 2 FeGeTe 4 magnetic semiconductor compounds. Magnetization measurements at 2, 4.2 and 77 K in magnetic fields up to 35 T were carried out on Cu 2 FeGeSe 4 compounds. From the analysis of the X-ray diffraction lines, it was found that Cu 2 FeGeSe 4 and Cu 2 FeGeTe 4 have, respectively, stannite and monoclinic structures. The resulting 1ac versus T curves showed that Cu 2 FeGeSe 4 is antiferromagnetic with a Ne  el temperature T N 20 K while Cu 2 FeGeTe 4 is ferrimagnetic with T N 160X1 K. The magnetization and susceptibility results obtained on Cu 2 FeGeSe 4 showed the presence of bound magnetic polarons (BMPs) in agreement with earlier studies made on this type of materials [1,2].

X-ray powder diffraction, differential thermal analysis, and magnetic susceptibility measurements on polycrystalline samples are used to determine the details of the T ( z ) phase diagram of the alloy system Cu~(l-,~Mn,Ga$3e~. At high temperatures, there is a single phase solid solution across the complete diagram in a disordered zincblende phase. However, at lower temperatures, the singlephase range is limited to relatively wide terminal fields, which are ordered structures based on a ziricblende subcell. Several different ordered phases are found to occur and the values of the Curie-Weiss constant 8 are used to investigate the changes in ordering with composition. It is shown that these ordering changes cause discontinuous changes in the slope of the graphs against composition of the lattice parameters, optical energy gap, and N8el temperature values.

Measurements of optical absorption in the temperature range 20 to 300K were made on polycrstalline samples of the compound CuGaTe 2 . These results were used to determine values of the optical energy gap E g as a function of temperature T. The resulting curves of E g vs T were fitted to a simplified Manoogian-Leclerc equation and the fitted coefficients used to give values of (dE g /dT) 1 and (dE g /dT) 2 , due to lattice dilation and electron-phonon contributions, respectively. Hence, the deformation potentials of the valence and conduction bands were estimated for the present compound.

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