Pressure-induced changes in transport properties of layered La_1.2Ca_1.8Mn₂O₇

The transport properties of a single crystal of La1.2Ca1.8Mn2O7 with the layered Sr3Ti2O7-type perovskite structure have been studied under hydrostatic pressures of up to similar to 9 kbar. It is found that La1.2Ca1.8Mn2O7 undergoes a first-order phase transition from a paramagnetic insulating to a low-temperature ferromagnetic metallic state which is accompanied by a large decrease in the electrical resistivity. At ambient pressure the magnetic phase transition takes place at T-c=242 K and as the external pressure is applied the critical temperature increases Linearly at a rate of 1.1 K/kbar. The present results reflect the competition between double and superexchange resulting from two-dimensional Mn-O-Mn networks and can be interpreted in terms of the exchange striction model.