Superparamagnetic Behaviour and Induced Ferrimagnetism of LaFeO3 Nanoparticles Prepared by a Hot-Soap Technique

Abstract

Lanthanum orthoferrite, LaFeO3 , is one of the most common perovskite-type oxides having an orthorhombic perovskite structure (space group Pbnm), where the distortion from the ideal cubic structure occurs to form the tilting of the FeO6 octahedra. LaFeO3 has much practical interest for electroceramic applications due to their attractive mixed conductivity displaying ionic and electronic defects [1, 2]. The mixed ionic-electronic conductivity of LaFeO3 exhibits a linear response to oxygen pressure and provides oxygen sensor applications [3]. The excellent sensitivity and selectivity towards various toxic gases such as CO and NOx are observed as well [4]. Moreover, LaFeO3 nanoparticles exhibited good photocatalytic properties such as water decomposition and dye degradation under visible light irradiation [5, 6]. These properties are enhanced by the homogeneity and high surface area of the fabricated LaFeO3 particles. Fine particles with diameter of less than 100 nm are potentially required for these purposes. Besides, the orthoferrites are known to be prototype materials for magnetic bubble devices because of their large magnetic anisotropy with small magnetization [7]. LaFeO3 is an interesting model system of orthoferrite antiferromagnets showing a weak ferromagnetism. The Néel temperature, TN , of LaFeO3 is 738 K, which is the highest temperature in the orthoferrite family [8]. The magnetic moments of Fe3+ ions are aligned antiferromagnetically along the orthorhombic a-axis. But they are slightly canted with respect to one another due to the presence of Dzyaloshinskii-Moriya interaction. A weak ferromagnetic component parallel to the c-axis appears. The magnetization of LaFeO3 bulk crystals is considerably small, 0.044 ?B/Fe [8]. However, magnetic structures of small particles are often different