Magnetism of the A -site ordered perovskites CaCu3Cr4O12 and LaCu3Cr4O12

Abstract

The microscopic magnetic nature of the $A$-site ordered chromium perovskites ${\mathrm{CaCu}}_{3}{\mathrm{Cr}}_{4}{\mathrm{O}}_{12}$ and ${\mathrm{LaCu}}_{3}{\mathrm{Cr}}_{4}{\mathrm{O}}_{12}$ and their solid-solution system, ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{Cu}}_{3}{\mathrm{Cr}}_{4}{\mathrm{O}}_{12}$, with $x=0.2$, 0.4, and 0.8, has been studied with muon spin rotation and relaxation (${\ensuremath{\mu}}^{+}\mathrm{SR}$) measurements down to 2 K using a powder sample. For ${\mathrm{CaCu}}_{3}{\mathrm{Cr}}_{4}{\mathrm{O}}_{12}$, ${\ensuremath{\mu}}^{+}\mathrm{SR}$ revealed the formation of static antiferromagnetic (AF) order below 122 K ($={T}_{\mathrm{N}}$), although magnetization measurements showed a very small change at ${T}_{\mathrm{N}}$. Analyses of the internal magnetic field ${H}_{\mathrm{int}}$ at the muon sites, predicted with first-principles calculations, suggested $G$-type AF order as a ground state. For ${\mathrm{LaCu}}_{3}{\mathrm{Cr}}_{4}{\mathrm{O}}_{12}$ with ${T}_{\mathrm{N}}=225$ K, ${\ensuremath{\mu}}^{+}\mathrm{SR}$ also supported the presence of a $G$-type AF ordered state, which was recently proposed based on neutron diffraction measurements. However, the ordered Cr moments were found to change the direction at around 10 K. For ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{Cu}}_{3}{\mathrm{Cr}}_{4}{\mathrm{O}}_{12}$, both ${T}_{\mathrm{N}}$ and ${H}_{\mathrm{int}}$ at 2 K increase monotonically with $x$.