Pressure-induced phase segregation in single-crystal La2-2xSr1+2xMn2O7 (x=0.32)

The temperature dependence of resistivity rho(T) and of the thermoelectric power alpha(T) of a single crystal of the ferromagnetic Ruddlesden-Popper c ompound La2-2xSr1+2xMn2O7 (x=0.32) have been measured under different hydro static pressures. Pressure induces segregation into antiferromagnetic elect ron-rich and ferromagnetic electron-poor Mn2O7 layers. With increasing pres sure, the ferromagnetic majority phase exhibits contraction of the apical ( Mn-O) bond and spin reorientation from the c axis to the basal plane at a c ritical pressure P-c(6 less than or equal to P(c)less than or equal to 7 kb ar). The phase segregation appears to reflect a first-order inversion of th e exchange coupling between ferromagnetic Mn2O7 layers.