Intralayer And Interlayer Exchange Tuned By Magnetic Field In The Bilayer Manganite (La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn(2)O(7) Probed By Inelastic Neutron Scattering

The bilayer manganite La(1.2)Sr(1.8)Mn(2)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 (La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn(2)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 Pr(3+) ion is considered to explain these results.