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Notes: SmMn2Ge2 shows reentrant ferromagnetism. Using flux grown single crystals we find that on cooling through the Curie temperature (Tt1=350 K) the material becomes ferromagnetic (FM). Upon further cooling, at Tt2=150 K an antiferromagnetic (AFM) phase is reached which is stable until Tt3=100 K when there is a transition to FM. The transitions at Tt1 and Tt2 are first order with a temperature hysteresis of about 4 K. Using ac susceptibility to determine the various transition temperatures as a function of pressure (P) we find that Tt3 rapidly decreases with increasing P and at relatively low pressures falls below our measuring range (90 K). Tt2 increases nearly linearly with P and reaches 330 K and 11 kbar. Tt1, drops slowly with increasing P and at 11 kbar the high temperature FM region ends. An x-ray determination of the lattice parameters (at atm pressure) shows that in the AFM region the a0 lattice parameter is decreased, discontinuously changing at Tt2 and Tt3. The c0 lattice parameter is essentially unchanged going through this transition region. These observations indicate that the magnetic properties of SmMn2Ge2 are very sensitive to interatomic spacing. Measurements with a differential scanning calorimeter show that, on heating, the transition at Tt2 is endothermic.

Notes: Pressure-tuned resonance Raman scattering (RRS) experiments in Ga1−xInxAs/Ga1−yAlyAs strained-layer quantum-well samples with x=0.15 and y=0.15, on a GaAs substrate, are reported. The photoluminescence (PL), 2LO-, and LO-phonon Raman-scattered intensities were followed as a function of pressure using the diamond cell. In backscattering geometry and with (100) samples, three sharply defined 2LO-phonon resonances are observed, at 2.1, 3.8, and 5.2 GPa, with 647.1-nm excitation ((h-dash-bar)ωL=1.916 eV), and these are identified to be from the AlGaAs, GaAs, and InGaAs layers, respectively. At the above pressures, the 2LO peak of the layer falls right on top of the PL peak of the corresponding layer, revealing that the resonance occurs when E0=(h-dash-bar)ωS (2LO). For the LO-phonon intensity, maxima are observed at 2.8 and 4.7 GPa, respectively, from the AlGaAs layer and GaAs substrate. While the LO-resonance profile (pressure versus phonon intensity) for the AlGaAs layer is narrow, the profile of the GaAs substrate layer is highly asymmetric. The InGaAs LO-resonance is totally masked by the strong GaAs LO phonon. The pressure dependence of the E0 gap, determined from PL data, reveals that the resonance condition for 2LO is E0=(h-dash-bar)ωS (2LO) and, for LO, E0=(h-dash-bar)ωL. Results with samples of different Al content and (h-dash-bar)ωL are consistent with the above conditions. A brief discussion of the theory of the RRS cross section is given, and it is suggested that the observed 2LO-resonance scattering is dominated by Frölich interaction, and that it could be a double resonance. The asymmetry in the LO resonance of the GaAs substrate, we believe, is due to the pressure-induced transparency, and this is a problem when dealing with pressure-tuned RRS, in multiple-quantum-well structure with GaAs or AlGaAs substrates. The usefulness of the 2LO resonance in locating the E0 gap is indicated, and the indistinguishability between luminescence and Raman scattering at the center of the 2LO resonance is pointed out. The need to study photoluminescence and Raman scattering in pressure-tuned RRS experiments is emphasized.