Charge Ordering and Phase Competition in the Layered Perovskite Lasr2mn2o7

TL;DR

This study investigates charge ordering and phase competition in layered perovskite LaSr2Mn2O7, revealing static charge order below 210 K, coexistence with antiferromagnetism, and weaker charge/orbital order compared to 3D manganites.

Contribution

It provides detailed insights into charge and orbital ordering, phase coexistence, and the competition between charge order and antiferromagnetism in layered manganite LaSr2Mn2O7.

Findings

Charge order appears below 210 K and becomes static.

Antiferromagnetism develops at 170 K and competes with charge order.

Charge and antiferromagnetic phases coexist as separate regions.

Abstract

Charge-lattice fluctuations are observed in the layered perovskite manganite LaSr2Mn2O7 by Raman spectroscopy as high as 340 K and with decreasing temperature they become static and form a charge ordered (CO) phase below TCO=210 K. In the static regime, superlattice reflections are observed through neutron and x-ray diffraction with a propagation vector (h+1/4,k-1/4,l). Crystallographic analysis of the CO state demonstrates that the degree of charge and orbital ordering in this manganite is weaker than the charge ordering in three dimensional perovskite manganites. A TN=170K a type-A antiferromagnetism (AF) develops and competes with the charge ordering, that eventually melts below T*=100K. High resolution diffraction measurements suggest that that CO- and AF-states do not coincide within the same region in the material but rather co-exist as separate phases. The transition to type-A antiferromagnetism at lower temperatures is characterized by the competition between these two phases.