Abstract
GdFeO3 perovskite attracted large interest in different fields thanks to peculiar magnetic and optical properties that are further tunable by means of doping processes and achievable on both Gd and Fe sites or by properly choosing the synthesis routes. In this paper, nanometric GdFeO3 compounds, undoped and doped with diamagnetic Ca2+ and Mg2+ ions, were synthesized by microwave assisted, sol–gel, and polyol syntheses and characterized by X-ray diffraction, showing solid solutions formation. Raman spectroscopy allowed us to confirm, from peak enlargements, the Ca and Mg substitution on Gd and Fe sites, respectively. The magnetic data showed the presence of magnetic domains as consequence of doping with diamagnetic ions, which seem to play a crucial role in the magnetic activity of the compounds. A superparamagnetic behaviour is evidenced; nevertheless, its intrinsic character is not definitely demonstrated. Indeed, the possible presence of traces of magnetic impurities, which are easily obtainable in these samples, such as iron oxides, must be taken into account.
Highlights
GdFeO3 is one of the most important members of the lanthanide metal oxide perovskites ABO3 (A = La, Sm, Eu, Gd) class
GdFeO3 perovskite attracted large interest in different fields thanks to peculiar magnetic and optical properties that are further tunable by means of doping processes and achievable on both Gd and Fe sites or by properly choosing the synthesis routes
Each of them was synthesized by the three following methods: 1. Microwave: Gd(NO3)3Á6H2O and Fe(NO3)3Á9(H2O) were mixed in the proper amount with an excess of citric acid (2:1 mol amount with respect to the sum of cations moles) used as a propellant to start the combustion reaction assisted by the microwaves [21]
Summary
The octahedron BO6, i.e. the basic unit for perovskite structure, has a great importance and an ‘‘octahedral factor’’ can be defined as rB/rO. By considering both these factors, the perovskites formability can be reliably predicted. GdFeO3 with a t value of 0.86 crystallizes in the orthorhombic space group Pnma showing a distorted perovskite-type structure, as a result of the FeO6 octahedra tilting, with Gd3? Fe spins (S = 5/2) order antiferromagnetically at the Neel temperature T(Fe) % 660 K and a weak ferromagnetic moment is observed due to the spin-canting associated to the Dzyaloshinskii–Moriya interactions in the iron-containing sublattice, as a result of the distorted perovskite structure [5,6,7,8,9,10,11]. From the optical point of view, GdFeO3 is a visible light active semiconductor with a narrow band gap (2.3 eV) [15]
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