Low-temperature neutron diffraction data on a ceramic sample of layered perovskite type La 2Ϫ2x Sr 1ϩ2x Mn 2 O 7 , xϭ0.3, are reported. The neutron diffraction data show that this compound undergoes a ferromagnetic transition at 100 K (T c ), but there is no antiferromagnetic signal as reported on a floating zone melt grown sample of the same nominal composition. The unit cell constants and cell volume for this nominal xϭ0.3 sample are slightly larger than those for samples which do show an antiferromagnetic component which indicates a higher Sr content. The magnetic structure was determined to have colinear Mn spins with a tilting angle against the c axis. The tilting angle abruptly increases from about 20°near T c to about 50°at 75 K and then gradually decreases afterwards to 30°at 15 K. This anomalous tilting angle behavior correlates with a distortion index based on the variance of the Mn-O bond distances and can be understood qualitatively with a simple crystal field argument. Below T c , there is a magnetostrictive effect on the c axis which correlates with the behaviors of the spin orientation and the Mn-O bond distances. ͓S0163-1829͑99͒08241-7͔
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