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Detailed structural and magnetic investigations have been performed on two equally Fe-doped MnCoGe alloys of nominal compositions Mn 0.875 Fe 0.125 CoGe and MnCo 0.875 Fe 0.125 Ge. The presence of martensitic phase transition (MPT) in both alloys is clear from the temperature variation of structural and magnetic properties. The nature of MPT is found to be complete in the Mn site Fe-doped alloy. On the other hand, a partial nature of the MPT is observed for the Co site Fe-doped alloy. The application of external hydrostatic pressure hardly affects the magnetic and structural transition temperatures. Both alloys show a significant amount of the magnetocaloric effect in ambient as well as in high pressure situation around their magnetic and structural transition regions. [ABSTRACT FROM AUTHOR]

Studies the kinetics of a structural phase transition in Langmuir monolayers of amphiphilic molecules. Microscopic relaxation mechanism in monolayers; Relationship between temperature and monolayer structure; rate of nucleation of a hexagonal phase from a metastable shear-induced structure.

We have studied the structure of a monolayer of C21H43OH on water, in the region near close packing, by grazing incidence in-plane x-ray diffraction. For all temperatures studied the isotherms in the πa plane show a kink, signaling a phase transition. Along an isotherm, and for pressures above the kink, we observe that the transverse structure factor has one peak which has constant position, width, and intensity; below the kink the diffraction peak shifts to smaller scattering vector (larger separation) and the amplitude decays as the surface pressure decreases, but the width of the peak remains constant. We rationalize these observations in terms of the influence on the transverse structure factor of gauche configurations in the amphiphile tails, with the kink representing the point at which the last of the gauche configurations is squeezed out of the chain. Along an isobar which is at higher pressure than the kink pressures of all isotherms crossed, the transverse structure factor has a single peak above a transition temperature and two peaks below that temperature; for π=30 dyn/cm the transition temperature is in the range 16.3