Pressure effects on the magnetic and transport properties of Pr1-xSrxMnO3 crystals near the percolation threshold

Effects of hydrostatic pressure up to 11kbar on the magnetic and transport properties of Pr1-xSrxMnO3 (PSMO) were investigated in single crystals with various doping level: x=0.22,0.24,0.26, in a wide range of temperature. In similarity with other low doped manganites, PSMO exhibits a metal to insulator transition and magnetoresistance maxima at the same temperature T=TMI. It was found that the magnetic ordering temperature TC of the Mn spin sublattice and TMI increase linearly upon applying the pressure. The pressure coefficients dTC dP and dTMI dP of PSMO enhance around percolation threshold at x=xC=0.24 upon increasing the doping level. According to the magnetization measurements it appears that the nature of the ferro-to-paramagnetic phase transition in PSMO also varies at the crossover region, in a similar manner to that of La1-xCaxMnO3. At ambient pressure the transition for x=0.22 is of a second order while for x=0.26 it is of a first order, a nature of a transition for x=0.24 is not well defined yet. The effect of pressure of ∼11kbar on the kind of the magnetic phase transition is clearly seen in the case of x=0.24 sample. Applied pressure changes the character of the phase transition from nearly a continuous one at P=0 to more abrupt, almost discontinuous one at P=10.7kbar. Measurements of magnetization and of ac susceptibility employed in our studies indicate upon an ordering of the Pr magnetic subsystem and a cluster glass behavior at temperatures TC(Pr) (80-100K), much lower than TC (165-205K). All of the results obtained are discussed with regards to existing models of magnetic and transport properties of low doped manganites.