Improvement of the multiferroic properties of lanthanum ferrites through cobalt doping
Description
LaFeO3 is a second-type multiferroic material, characterized by an improper ferroelectricity, which is induced by the magnetic order of the material. However, it shows antiferromagnetic order which limits their applications. In order to induce ferromagnetism, in the present work is studied the effects of Co2+ doping in LaCoxFe1-xO3, with x varying from 0 to 0.5, Δx=0.1 on the crystal structure, magnetic and dielectric properties. Moreover, it is described the mechanism responsible for the ferromagnetism in doped ferrites. The XRD results show that at doping levels lower than 0.3 mol, LaFeO3 maintains its orthorhombic structure (Pnma), whereas at higher cobalt concentrations, the rhombohedral (R3c) LaCoO3 phase emerges. In addition, it is observed that cobalt doping induces ferromagnetism as a consequence of the cobalt occupying iron positions until the solubility limit is reached and the formation of Fe doped LaCoO3. All samples present high relative permittivity values, which increase with cobalt content. Furthermore, the presence of cobalt leads to a reduction in the dielectric dissipation factor, attributed to decreased crystal structure distortion.
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Steps to reproduce
Cobalt-doped lanthanum ferrite with a general formula of LaFe1-xCoxO3 (with x varying from 0 to 0.5 and Δx = 0.1) was synthesized by means of thermal-assisted high-energy ball milling. Five grams of stoichiometric amounts, the following raw materials were used: iron oxide (Fe2O3, Sigma Aldrich, 99.9% purity), lanthanum oxide (La2O3, Sigma Aldrich, 99.9% purity) and cobalt oxide (CoO, Sigma Aldrich, 99.9% purity), which were loaded into steel vials with a 10:1 ball-to-powder ratio and subjected to milling in a Spex 8000 D mill for 5 h at intervals of 90 min with 30 min of cooling time between each interval. The milling was assisted by thermal treatment for 7 h at 1200 °C. Cylindrical pellets 10 mm in diameter were prepared by using heat-treated powders under a uniaxial pressure of 1500 MPa followed by sintering at 1200 °C for 7 h.
Institutions
- Instituto Politecnico NacionalDistrito Federal, Ciudad de Mexico