Orbital order-disorder transition in La(1-x)Nd(x)MnO(3) (x = 0.0-1.0) and La(1-x-y)Nd(yx)Sr(y)MnO(3) (x = 0.1; y = 0.05,0.1)

TL;DR

This study investigates the orbital order-disorder transition in La(1-x)Nd(x)MnO(3) and Sr-doped variants, revealing a shift from first to higher order transitions with doping and highlighting the robustness of orbital order.

Contribution

It provides detailed analysis of how doping affects the order of the transition and the associated latent heat, offering new insights into the orbital domain evolution in manganites.

Findings

Transition order shifts from first to higher order with increasing x.

Latent heat decreases steeply then gradually with x.

Transition temperature increases with <r(A)> and <cos^2(phi)>.

Abstract

The nature of orbital order-disorder transition has been studied in the La(1-x)Nd(x)MnO(3) (x = 0.0-1.0) series which covers the entire range between two end points - LaMnO(3) and NdMnO(3) - as well as in La(0.85)Nd(0.1)Sr(0.05)MnO(3) and La(0.8)Nd(0.1)Sr(0.1)MnO(3). It has been observed that the first-order nature of the transition gives way to higher order with the increase in "x" in the case of pure manganites. The latent heat (L) associated with the transition, first, drops with a steeper slope within x = 0.0-0.3 and, then, gradually over a range 0.3<x<0.9. This drop could, possibly, be due to evolution of finer orbital domain structure with "x". In the case of Sr-doped samples, the transition appears to be of higher-order nature even for a doping level 5 at%. In both cases, of course, the transition temperature T(JT) rises systematically with the drop in average A-site radius <r(A)> or rise in average Mn-O-Mn bond bending angle <cos^2(phi)> while no apparent correlation could be observed with doping induced disorder sigma^2. The cooperative nature of the orbital order, therefore, appears to be robust.