Intralayer and interlayer exchange tuned by magnetic field in the bilayer manganite(La0.4Pr0.6)1.2Sr1.8Mn2O7probed by inelastic neutron scattering

Abstract

The bilayer manganite ${\text{La}}_{1.2}{\text{Sr}}_{1.8}{\text{Mn}}_{2}{\text{O}}_{7}$ (LSMO) exhibits a phase transition from a paramagnetic insulating (PI) to a ferromagnetic metallic (FM) state with a colossal magnetoresistance (CMR) effect. Upon 60% Pr substitution, both the magnetic order and the PI to FM transition are suppressed. However, application of a magnetic field induces a first-order transition to a FM state with a CMR effect. We report here inelastic neutron scattering from a single crystal of ${({\text{La}}_{0.4}{\text{Pr}}_{0.6})}_{1.2}{\text{Sr}}_{1.8}{\text{Mn}}_{2}{\text{O}}_{7}$ under a magnetic field of 3.7 T, applied along the $c$ axis and along the [110] direction. Our data reveal the in-plane exchange ${J}_{ab}$ close to that of the Pr-free compound LSMO although the interlayer exchange ${J}_{c}$ is much smaller than that found in LSMO. Anisotropic lattice distortion induced by the smaller size of ${\text{Pr}}^{3+}$ ion is considered to explain these results.