Absence of Long Range Magnetic Order in the La1.4Sr0.8Ca0.8Mn2O7 Bilayered Manganite

TL;DR

This study reveals that the La1.4Sr0.8Ca0.8Mn2O7 bilayered manganite lacks long-range magnetic order despite exhibiting insulator-metal transitions, suggesting transport is influenced by two-dimensional spin correlations rather than three-dimensional magnetic order.

Contribution

First demonstration of the absence of long-range magnetic order in optimally doped bilayered manganite with mixed Ca and Sr doping using neutron diffraction.

Findings

No long-range magnetic order detected in the studied manganite.

Transport properties are independent of magnetic order and linked to two-dimensional spin correlations.

Size mismatch between Ca and Sr ions may suppress magnetic order.

Abstract

In this work we studied, by means of high-resolution neutron diffraction as a function of temperature, the La1.4Sr0.8Ca0.8Mn2O7 bilayered manganite for two different annealing treatments. Out data allowed us to shown, for the first time, the absence of long-range magnetic order in this optimally doped bilayered manganite where the A-site of the structure is doped with equal proportions of different isovalent cations (Ca and Sr). The system, however, presents defined IM transitions which suggest that the transport properties are not linked to the evolution of long-range order and that two dimensional spin ordering in the layers of the perovskite blocks may be sufficient to 'assist' the hole hopping. Possible reason for the suppression of magnetic order induced by the Ca doping is a size effect coupled to the cation size mismatch between the Sr and Ca ions.