Pressure induced insulator-metal transition and giant negative piezoresistance in Pr0.6Ca0.4Mn0.96Al0.04O3 polycrystal

The effect of external hydrostatic pressure (P) on the magnetization (M) and resistivity (ρ) properties of charge-orbital (CO) ordered-insulating phase-separated manganite Pr0.6Ca0.4Mn0.96Al0.04O3 system is reported here. At ambient P, CO ordering transition and spin-canting in the AFM are observed at 223 K and 55 K respectively in M(T) and ρ(T) measurements. Application of P increases simultaneously the magnitude of magnetization (M) and transition temperature, and weakens the CO ordering in M(T) measurements up to 0.98 GPa. During ρ(T) measurements, P induces an insulator-metallic transition (TIM) at 1.02 GPa, and further increase of P up to 2.84 GPa leads to increase of TIM (dTIM/dP =21.6 K/GPa). ρ at TIM is reduced about three orders of magnitude at 2.84 GPa, and leads to the giant negative piezoresistance (~98%). These results are analyzed separately in two temperature regions i.e., below and above TIM by power function equation and small polaronic hopping model respectively. It is understood from these analyses that the application of P suppresses the Jahn-Teller distortions, electron-electron and electron-magnon scattering factors, and induces the insulator-metal transition in Pr0.6Ca0.4Mn0.96Al0.04O3 system.