Anisotropic Magnetoelastic Phenomena in Layered Manganite Crystals: Implication of Change in Orbital State

Magnetoelastic phenomena correlated with magnetoresistive ones have been investigated for bilayered manganite crystals, La_2-2xSr₁₊₂ₓMn₂O₇ ( 0.3≤x≤0.45), by measurements of the striction parallel and perpendicular to the MnO₂ plane in magnetic fields. The magnetization process causes not only a large negative magnetoresistance but also a gigantic lattice striction which is highly anisotropic with respect to the crystal axes. The magnitude and the sign of the lattice striction systematically varies with the doping level ( x), which should reflect variation of the orbital-dependent occupancy in the two-dimensional conduction band with temperature, magnetic field, and doping level.