Quantum magnons of the intermediate phase of half-doped manganite oxides

BUITRAGO, I. R.; VENTURA, CECILIA; L. O. MANUEL

IEEE TRANSACTIONS ON MAGNETICS

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

Lugar: New York; Año: 2013 vol. 49 p. 4691 - 4694

0018-9464

At half doping, the ground state of three-dimensional manganite perovskite oxides like R1xCaxMnO3, where R is a trivalent ion such as La, Pr, etc, is still unclear. Many experimental findings agree better with the combined magnetic, charge and orbital order characteristic of the ?intermediate phase?, introduced by Efremov et al. in 2004 [Nature Mats. 3, 853]. This phase consists of spin dimers (thus incorporating aspects of the Zener polaron phase (ZP) proposed in 2002 by Daoud-Aladine et al. [Phys. Rev. Lett. 89, 097205]), though formed by a pair of parallel Mn spins of different magnitude, in principle (thereby allowing for a degree of Mn charge disproportionation: not necessarily as large as that of Mn3+-Mn4+ in Goodenough?s original CE phase [Phys. Rev. 100, 564 (1955)] ). In the intermediate phase, consecutive spin dimers localed along the planar zig-zag chains are oriented at a constant relative angle between them. Varying Mn-charge disproportionation and , the intermediate phase should allow to continuously interpolate between the two limiting cases of the CE phase and the dimer phase denoted as ?orthogonal intermediate phase?. It is not easy to find a microscopic model able to describe the phenomenological intermediate phase adequately for the spin, charge, and orbital degrees of freedom simultaneously. Here, we study the quantum spin excitations of a planar model of interacting localized spins, which we found can stabilize the intermediate phase classically. We compare the quantum magnons of the intermediate phase with those of the CE and orthogonal phases, in the context of recent experimental results.