Lattice effects and magnetic structure in the layered colossal magnetoresistance manganite La2-2xSr1+2xMn2O7, x = 0.3

We report on the temperature dependence of the crystal and magnetic structu re of the layered colossal magnetoresistive manganite, La2-2xSr1+2xMn2O7, x = 0.3. Neutron-diffraction measurements show that the insulator-metal (IM) transition (T-IM) at similar to 100 K is accompanied by a ferromagnetic (F M) ordering of spins within MnO6 bilayers (intrabilayer coupling), but with an antiferromagnetic coupling between neighboring bilayers (interbilayer c oupling). Below T-IM, the Mn spins rotate from similar to 45 degrees inclin ation to the c axis until they are almost parallel to the c axis at 5 K. Co incident with this spin reorientation, a FM c axis component develops below 75 K. Evidence from both neutron and synchrotron x-rap-diffraction experim ents suggest that the FM c-axis magnetic moment results from a second layer ed manganite phase with composition 0.3 less than or equal to x less than o r equal to 0.32. This observation emphasizes the need for thorough examinat ion of the homogeneity when measuring bulk properties (e.g., magnetization, transport) of nominally x=0.3 samples. Associated with the electronic and magnetic transitions, a pronounced lattice response along the c axis (obser ved in both phases) signals a transfer of charge into d(x2)-(y2) orbitals i n the low-temperature phase. That the lattice effects here are opposite in sign to those observed in the x=0.4 layered manganite points to the sensiti vity of the spin-lattice-charge coupling to dopant concentration in these r educed-dimensionality manganites. [S0163-1829(99)00513-5].