Pressure-enhanced ferromagnetism and metallicity in La1.24Sr1.76Mn2O7 bilayered manganite system
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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 (T C) accompanied by a metal–insulator transition (T MI) at 130 K. We observe that the T C and T MI increase with hydrostatic pressure at a rate of dT C/dP = 2.08 K/kbar and dT MI/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 T C and at 4.2 K upon an external magnetic field of 5 T. The observed MRR at T C 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.
KeywordsMn2O7 Hydrostatic Pressure Manganite Applied Pressure Charge Transport
M.K. is thankful to FCT, Portugal for the grant SFRH/BPD/75110/2010. This work was supported by the CNPq, Brazil and TWAS, Italy.