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Signs of superparamagnetic cluster formation in Lu Fe 1 − x Cr x O 3 perovskites evidenced by magnetization reversal and Monte Carlo simulations

2021; American Physical Society; Volume: 103; Issue: 1 Linguagem: Inglês

10.1103/physrevb.103.014447

2469-9977

Florencia E. Lurgo, Orlando V. Billoni, Vladimir Pomjakushin, Juan Pablo Bolletta, C. Martin, A. Maignan, Raúl E. Carbonio,

Advanced Condensed Matter Physics

In this paper, we study the magnetic properties of orthorhombic (Pbnm) perovskites $\mathrm{Lu}{\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{3}$ with $x=0.25$, 0.45, 0.55, and 0.75 by magnetization vs temperature and neutron powder diffraction measurements at room temperature. The magnetic moments are oriented along the $x$ direction with a G-type antiferromagnetic (AFM) arrangement that corresponds to irreducible representation ${\mathrm{\ensuremath{\Gamma}}}_{4}$ (${G}_{x}{A}_{y}{F}_{z}$). Magnetization reversal (MR) is observed for $0.45\ensuremath{\le}x\ensuremath{\le}0.75$. The MR phenomenon was modeled using Monte Carlo simulations, modeling both homogeneous and inhomogeneous cation distributions. For $\mathrm{Lu}{\mathrm{Fe}}_{0.25}{\mathrm{Cr}}_{0.75}{\mathrm{O}}_{3}$, the presence of MR could only be explained using an inhomogeneous distribution with well-defined magnetic clusters. Looking at the staggered magnetization of each cluster, we propose a superparamagnetic regime of ${\mathrm{Fe}}^{3+}$ clusters in a ${\mathrm{Cr}}^{3+}$-rich matrix for $\mathrm{Lu}{\mathrm{Fe}}_{0.25}{\mathrm{Cr}}_{0.75}{\mathrm{O}}_{3}$. By calculating the specific heat, we found that, in $\mathrm{Lu}{\mathrm{Fe}}_{0.45}{\mathrm{Cr}}_{0.55}{\mathrm{O}}_{3}$ and $\mathrm{Lu}{\mathrm{Fe}}_{0.25}{\mathrm{Cr}}_{0.75}{\mathrm{O}}_{3}$ the clusters order at nearly the same temperature ${T}_{N}^{\mathrm{Clus}}\ensuremath{\sim}535$ and 520 K, respectively, while the matrix orders at ${T}_{N}^{\mathrm{Mat}}\ensuremath{\sim}115\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. There is considerable reduction in the cluster ordering temperature as compared with the bulk, as ${T}_{N}\ensuremath{\sim}628\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for $\mathrm{LuFe}{\mathrm{O}}_{3}$, while the matrix orders at the expected temperature as ${T}_{N}\ensuremath{\sim}115\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for $\mathrm{LuCr}{\mathrm{O}}_{3}$.