Abstract
We report the low temperature magnetization, electrical resistance, and magnetoresistance of La1.24Sr1.76Mn2O7 bilayer manganite system under hydrostatic pressure. At ambient pressure, the compound shows a sharp ferromagnetic transition (TC) accompanied by a metal–insulator transition (TMI) at 130 K. We observe that the TC and TMI increase with hydrostatic pressure at a rate of dTC/dP = 2.08 K/kbar and dTMI/dP = 2 K/kbar, respectively. Also, we observe an appreciable increase of magnetic moments at low temperatures with increasing pressure. The high temperature regime of temperature dependence of resistivity curves was fitted with the Emin–Holstein’s polaron hopping model and the calculated activation energy values suggest that the applied pressure weakens the formation of Jahn–Teller polarons. The magnetoresistance ratio (MRR) was measured at TC and at 4.2 K upon an external magnetic field of 5 T. The observed MRR at TC is about 210 % and the applied pressure increases the MRR significantly. These results can be interpreted by the pressure-enhanced overlap between the orbitals of Mn–O–Mn, which facilitates the charge transfer and hence enhances the ferromagnetism and metallicity.
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