Lattice variation, reentrant electric properties, and magnetic order in bilayered La1.02Sr1.98Mn2O7

Neutron diffraction, de electric resistivity, and ac magnetic susceptibilit y measurements were performed to study the structural, electric, and magnet ic properties of naturally bilayered La1.02Sr1.98Mn2O7. An insulator to met al transition was clearly seen at similar to 170 K. Below 60 K, the system reentered the insulating state. Three-dimensional (3D) long-range order of the nhl spins was found, with an ordering temperature of T-m approximate to 180 K and a saturated moment of [mu(Z)] = 2.70(2)mu(B). The in-plane coupl ings were ferromagnetic. Within each bilayer, simple antiferromagnetic coup lings between the ferromagnetic sheets were found, whereas the neighboring bilayers were coupled ferromagnetically. A structural change that results i n a reduction of the thermal contraction rate occurs at similar to 250 K as well. (C) 2000 Elsevier Science S.A. All rights reserved.