The effects of external (hydrostatic) pressure and internal (chemical) pressure on the transport and magnetic properties of the La1.4Sr1.6Mn2O7 are investigated. Both metal-insulator transition temperature T-m and Curie temperature T-C increase with the increase of external pressure. In contrast, the T-m and T-C decrease with the increase of Ca content in La-1.4(Sr1 - xCax)(1.6)Mn2O7 (x less than or equal to 0.3), where the internal pressure is supposed to be introduced. External pressure enlarge the ferromagnetic metal phase through the pressure-enhanced transfer interaction of the charge carriers. The Mn-O-Mn bond angle remains almost unchanged with the increase of Ca content which is in sharp contrast to the La1 - xSrxMnO3 system. The Mn-O(3) bond length is decreased by the external pressure while increased by the internal pressure. It is interpreted that the opposite behaviors of T-m and T-C for external and internal pressures are due to the different variations of Mn-O(3) bond length. All other results are discussed and compared with those in the (La,Sr)MNO3 system. [S0163-1829(98)06642-9].
