Pressure induced canted ferromagnetic order in La1.32Sr1.68Mn2O7 layered manganite

The electrical resistance, magnetization and magnetoresistance of La1.32Sr1.68Mn2O7 layered manganite have been studied under hydrostatic pressure and magnetic field. At ambient pressure, the temperature dependence of the magnetization shows a ferromagnetic to paramagnetic transition at 118 K. Close to this transition, we have also observed a metal-insulator transition at T = T1MI in the temperature dependence of the resistivity ρ(T) measurement. The increasing pressure enhances a second metal-insulator transition T2MI at a critical pressure 6 ≤ PC ≤ 7 kbar. With further increasing pressure, both the T1MI and T2MI shift to high temperatures and the peak resistivity suppresses abruptly. We could not observe any transition correspond to T2MI in the temperature dependence of the magnetization up to 10.2 kbar. A large negative tunneling magnetoresistance was observed around TC in the field dependence of the ρ(T) curves and the pressure reduces magnetoresistance ratio significantly. From our results, we argue that the increasing pressure induces a canted ferromagnetic order which leads to a ferromagnetic insulating phase at low temperature.