Powder neutron diffraction evidence for enhanced inter plane magnetic coupling in La(1.2)Sr(1.8)Mn(2-x)Ru(x)O(7) layered manganites

Abstract

Rotation of Mn spin moments along the c axis enhances interplane magnetic coupling, leading to a steep increase in the Curie temperature (T(C)) and metal to insulator transition (T(MIT)) in Ru substituted two dimensional layered manganites, La(1.2)Sr(1.8)Mn(2-x)Ru(x)O(7). The temperature dependent neutron diffraction data show the absence of (004) reflection, indicating that the Mn spin moments are not aligned in the a-b plane, and rather the increase in intensity of (110) reflection at 12 K shows that the MnO(2) layers are stacked ferromagnetically along the c axis. The presence of Ru at the Mn site in pentavalent state assures the required hole carrier density for a sustained double-exchange interaction. The cumulative effect of rotation of Mn spin moments and the variable valence states of Ru lead to a pronounced increase in T(C) up to similar to 50 K, which is not observed hitherto in any of the B-site substituted manganites. (c) 2007 American Institute of Physics.