Spin-reorientation transition at isoelectronic substitution in double-layer manganites (La1−z Prz)1.2Sr1.8Mn2O7

The transport, magnetic, and thermal properties of single crystal double-layer manganites of the Ruddlesden-Popper series (La1−z Prz)1.2Sr1.8Mn2O7 (z=0.1 or 0.4) were studied. The compounds exhibit the colossal negative magnetoresistance effect in the region of a transition into a ferromagnetic state. Upon the isoelectronic substitution of Pr3+ for La3+, the Curie temperature decreases, while the easy magnetization axis rotates from the ab plane to the c axis. The observed effect is related to a change in the occupancy of dx²-y² and d3z²-r² orbitals as a result of stretching of the MnO6 octahedra.