PRESSURE EFFECT ON THE GMR MATERIAL TL2MN2O7 WITH THE PYROCHLORE STRUCTURE

The influence of hydrostatic pressure on the magnetic and electronic p roperties of a new class of manganese oxide-based giant magnetoresista nce (GMR) materials, represented by electron-doped Tl2Mn2O7, has been studied. It was found in this study, that the applied pressure causes the Curie temperature T-c of Tl2Mn2O7 to decrease at a modest rate of -1.6K/GPa. Negative pressure coefficient dTc/dP=-0.4 K/GPa was observe d for an isostructural insulator In2Mn2O7 as well. The results, togeth er with the temperature dependent multiple changes of the sign of the pressure coefficient of resistivity d rho/nP, are in sharp contrast wi th the case of the perovskite GMR oxides, where strong positive effect of pressure on both the T-c and conductivity was reported in agreemen t with a double exchange theory.