Signs of superparamagnetic cluster formation in LuFe1-xCrx O3 perovskites evidenced by magnetization reversal and Monte Carlo simulations

Abstract

In this paper, we study the magnetic properties of orthorhombic (Pbnm) perovskites LuFe1-xCrxO3 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 Γ4 (GxAyFz). Magnetization reversal (MR) is observed for 0.45≤x≤0.75. The MR phenomenon was modeled using Monte Carlo simulations, modeling both homogeneous and inhomogeneous cation distributions. For LuFe0.25Cr0.75O3, 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 Fe3+ clusters in a Cr3+-rich matrix for LuFe0.25Cr0.75O3. By calculating the specific heat, we found that, in LuFe0.45Cr0.55O3 and LuFe0.25Cr0.75O3 the clusters order at nearly the same temperature TNClus∼535 and 520 K, respectively, while the matrix orders at TNMat∼115K. There is considerable reduction in the cluster ordering temperature as compared with the bulk, as TN∼628K for LuFeO3, while the matrix orders at the expected temperature as TN∼115K for LuCrO3.