Hydrostatic pressure effect on electrical and magnetic properties of electron-doped R0.16Ca0.84MnO3 (R=Pr, Gd, Eu)

Temperature dependences of resistivity and magnetization of electron-doped R0.16Ca0.84MnO3 (R=Pr, Gd, Eu) orthomanganites have been studied under applied pressures up to 11kbar. For Pr0.16Ca0.84MnO3, the transition temperature between antiferromagnetic insulating and paramagnetic semi-metallic state Tt decreases under pressure at the rate dTt/dP=-0.3K/kbar. The sign of the effect is opposite and the value is an order of magnitude lower than that for ferromagnetic metallic hole-doped R1-xDxMnO3 (xC<x<0.5, D=Ca, Sr, xC-percolation threshold) compounds. The negative sign of the effect is in evident contradiction with a positive shift of the magnetic transition temperature of the parent compound CaMnO3. To interpret this result, a possibility of electron delocalization and a crossover to a band antiferromagnetism by electron doping have been suggested. The compounds Eu0.16Ca0.84MnO3 and Gd0.16Ca0.84MnO3 below Tt are in a mixed magnetic state with coexisting ferro- and antiferromagnetic exchange interactions. The weak pressure effect on Tt for Eu0.16Ca0.84MnO3 does not correlate with the record of the magnetoresistance effect of electron-doped compounds. Considering the obtained applied pressure data, the role of interatomic distances in the formation of CMR effect for electron-doped orthomanganites is discussed