Phase Separation in A-site Ordered Perovskite Manganite LaBaMn$_2$O$_6$ Probed by $^{139}$La and $^{55}$Mn NMR

TL;DR

This study reveals that LaBaMn$_2$O$_6$ exhibits a phase-separated ground state with coexisting ferromagnetic and antiferromagnetic regions below 200 K, characterized by NMR spectroscopy, indicating a mesoscopic scale of phase separation.

Contribution

The paper demonstrates the coexistence of ferromagnetic and antiferromagnetic phases in A-site ordered LaBaMn$_2$O$_6$ using NMR, highlighting a mesoscopic phase separation mechanism.

Findings

Coexistence of FM and AFI(CE) regions below 200 K.

The FM phase in LaBaMn$_2$O$_6$ is similar to that in disordered La$_{0.5}$Ba$_{0.5}$MnO$_3$.

Phase separation occurs on a mesoscopic scale.

Abstract

$^{139}$La- and $^{55}$Mn-NMR spectra demonstrate that the ground state of the A-site ordered perovskite manganite LaBaMn$_2$O$_6$ is a spatial mixture of the ferromagnetic (FM) and antiferromagnetic (AFI(CE)) regions, which are assigned to the metallic and the insulating charge ordered state, respectively. This exotic coexisting state appears below 200 K via a first-order-like formation of the AFI(CE) state inside the FM one. Mn spin-spin relaxation rate indicates that the FM region coexisting with the AFI(CE) one in LaBaMn$_2$O$_6$ is identical to the bulk FM phase of the disordered form La$_{0.5}$Ba$_{0.5}$MnO$_3$ in spite of the absence of A-site disorder. This suggests mesoscopic rather than nanoscopic nature of FM region in LaBaMn$_2$O$_6$\@.