Heavily doped bilayer manganites: links among structure, charge, and spin

Abstract.

Bilayer manganites La_2-2xSr_1+2xMn₂O₇ offer an exceptional opportunity to explore the connections among crystal structure, magnetic structure, and charge order. We have recently succeeded in synthesis of the phase diagram for x>0.5, and have used both neutron and X-ray diffraction to explore this highly Mn⁴⁺-rich system. In particular, we find a progression of magnetic structures from the type-A layered antiferromagnetic (AF), through the type-C AF rod structure, and finally to the type-G ‘rock salt’ AF structure. We also discover an unexpected region in which no long-range magnetic order is found and discuss a possible frustration scenario based on incompatible orbital ordering. We also address the evolution of charge order in these materials.