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We present the observation of temperature-induced transition between ferromagnetic (FM) and antiferromagnetic (AFM) interlayer exchange coupling (IEC) in trilayer structures consisting of two (Ga,Mn)(As,P) ferromagnetic layers and a GaAs:Be spacer. Hall resistance measurements were performed on trilayers prepared in as-grown and annealed states. Anomalous Hall resistance (AHR) measurements show two-step hysteresis loops, indicating that coercive fields of the two (Ga,Mn)(As,P) layers in the trilayer are different. Minor loops of AHR show characteristic shifts that correspond to FM IEC at low temperatures and AFM IEC at high temperatures in both as-grown and annealed samples. This temperature-induced transition from FM to AFM IEC occurs at a lower temperature in the annealed sample than in the as-grown sample. We attribute such an enhanced IEC transition effect in the annealed sample to the increase of carrier concentrations obtained by annealing, a characteristic feature of ferromagnetic semiconductors. The observation of AFM IEC in the (Ga,Mn)(As,P)-based trilayer suggests the possibility of realizing synthetic antiferromagnetic systems in such structures, which can be used for antiferromagnetic spintronic device applications.

In this paper, we study the polytype transformation of cubic silicon carbide (3C-SiC) by micro Raman spectroscopy. Two sets of samples are investigated. First, physical vapor transport (PVT) grown samples, grown on chemical vapor deposition (CVD) substrates at growth temperatures between 1800 and 1950°C. The microscopic images of the cross sections and the Raman spectra taken on these grown crystals show a growing fraction of 6H-SiC inclusions with increasing growth temperature. To decide whether these polytype inclusions are induced by the PVT growth process or by the temperature treatment of the CVD substrates, we studied the temperature induced polytype coversion of cubic CVD substrates grown on undulant Si(100) surfaces which were used as seed crystals for the PVT growth. The CVD substrates were annealed in the temperature range between 1700 and 2100°C. The results of this annealing series are similar to the results we find in the PVT grown samples. Therefore we argue that the polytype conversion is not induced by the PVT growth process but a result of the heat treatment of the CVD seed crystals.

Variable temperature scanning surface potential microscopy is used to determine thermodynamic and kinetic parameters associated with polarization screening on BaTiO3(100) surfaces. The temperature dependence of the surface potential is indicative of the interplay between the fast dynamics of atomic polarization and slower dynamics of screening charge. The screening charge relaxation kinetics are found to be weakly dependent on temperature with activation energy Ea∼4 kJ/mole. Equilibrium domain potential difference depends linearly on temperature; the zero potential contrast is observed at ∼110 °C. At room temperature the sign of domain potential is determined by the screening charges rather than polarization charge. A thermodynamic model for screening of ferroelectric surfaces based on Ginzburg–Devonshire theory is developed so that the enthalpy and entropy of charge compensation can be derived from the temperature dependence of surface potential contrast. In the case of BaTiO3 in air, the charge compensa...

Different morphologies of graphene can provide a great potential for applications of graphene-based nano-devices and functional nano-materials. Using molecular dynamic simulations, we show that by altering the temperature, one can induce unfolding of short (length less than ∼50 nm) scrolled or folded graphene to a planar state. The mechanism of these phenomena is that temperature modifies the stability of these unclosed structures. We show in particular that morphology transformation of graphene is not explained by the change of the potential energy of the system, but rather it can be explained by a free energy analysis based on thermal dynamics.

The rise in temperature induced by heating a surface with a cw Gaussian laser is analytically related to the Raman Stokes/anti-Stokes intensity ratio measured by the same laser to induce the heating, for an idealized, though often experimentally-relevant, set of conditions. For a range of conditions, the peak temperature rise is actually twice that determined from this ratio if one were to assume a spatially uniform temperature rise. This shows that care must be exercised in determining temperature from Stokes/anti-Stokes ratios.

A temperature-induced transition from homeotropic to tilted alignment in the nematic phase of a liquid crystal with smectic C-nematic phase sequence was observed. The homeotropic alignment of the nematic phase at temperatures near the nematic-isotropic transition was found to undergo a continuous change to tilted one on decreasing the temperature. The appearance of smectic-C-like order at the solid surface on approaching the smectic C-nematic transition is assumed to be the origin of this temperature-induced alignment transition.

The Hugoniot of wrought tungsten which was 99.6% of the crystalline density and 99.92% pure has been determined to 80 kbar at room temperature and at 950°C. Measurements of the stress‐particle velocity relationship were made by impacting a sapphire‐faced quartz gauge assembly onto the tungsten sample. In the room temperature experiments, transmitted wave profiles were determined with quartz gauges. At room temperature, the elastic wave velocity was 5.22±0.05 mm/μsec and the Hugoniot elastic limit for 9.5 mm thick specimens was 37.7±0.8 kbar. The stress‐particle velocity Hugoniot at 950°C, while nearly parallel to the room temperature Hugoniot, was displaced about 15 kbar downward due to a decrease in the Hugoniot elastic limit at this temperature. This decrease is associated with a temperature induced brittle‐ductile transition. The application of these data in calculating the Gruneisen parameter is discussed.

Frame‐camera interferogram data for a neodymium‐doped glass rod taken during the laser pumping process have been analyzed in terms of changes in optical path length due to: (1) explicit temperature‐induced changes in length and index of refraction, and (2) temperature‐induced stress birefringence. Criteria for compatibility of the interferogram data, the formalism, and independently determined values for the phenomenological constants involved are set up and met, after which the temperature over the rod cross section obtains. The minimum in the temperature distribution found accounts for the observed split fringes, and our qualified estimate of the temperature rise at the center of the rod is ∼16°C. Estimates of the changes in optical path length due to the various effects are made, and values for the temperature coefficients of expansion and refractive index of 0.97×10−5/°C±6% and −7.2×10−7/°C±60%, respectively, are submitted.