Crystal structures and magnetic properties of strontium and copper doped lanthanum ferrites

• Published in: Journal of solid state chemistry Vol. 191; pp. 33 - 39
• Main Authors: Natali Sora, Isabella, Caronna, Tullio, Fontana, Francesca, de Julián Fernández, César, Caneschi, Andrea, Green, Mark
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.07.2012; Elsevier
• Subjects: ANTIFERROMAGNETISM; Cations; Condensed matter: structure, mechanical and thermal properties; Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder; COPPER; Cross-disciplinary physics: materials science; rheology; Crystal structure; Crystalline state (including molecular motions in solids); CRYSTALS; DOPED MATERIALS; Exact sciences and technology; FERRITE; FERRITES; INTERACTIONS; IRON; LANTHANUM; Lanthanum ferrites; Magnetic moment; MAGNETIC MOMENTS; MAGNETIC PROPERTIES; Magnetic structure; MATERIALS SCIENCE; NEUTRON DIFFRACTION; Neutron diffraction and scattering; Neutron powder diffraction; ORTHORHOMBIC LATTICES; PEROVSKITE; Perovskite oxides; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; PHASE SPACE; Physics; Single-crystal and powder diffraction; SPACE GROUPS; STRONTIUM; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; TEMPERATURE RANGE 0273-0400 K; Theory of crystal structure, crystal symmetry; calculations and modeling; TRIGONAL LATTICES; Weak ferromagnetic interactions; Perovskite oxides; Lanthanum ferrites; Neutron powder diffraction; Weak ferromagnetic interactions; Antiferromagnetism; Rietveld method; Cubic lattices; Space groups; Iron oxide; Neutron diffraction; Doping; Distortion; Iron; Symmetry groups; Bond lengths; Structural models; Lanthanum oxide; Unit cell; Trigonal lattices; Coercive force; Crystallographic site; Iron Strontium Oxides Mixed; Magnetic structure; Copper; Phase space; Iron Lanthanum Oxides Mixed; Magnetic properties; Crystal structure; Temperature dependence; Phase transformations; Magnetic model; Magnetic ordering; Perovskites; Hexagonal lattices; Powder pattern; Valence; Transition elements; Orthorhombic lattices; Exchange interactions
• DOI: 10.1016/j.jssc.2012.02.020
• ISSN: 0022-4596

The crystal and magnetic structures of La0.8Sr0.2Fe1−xCuxO3−w compounds, which exhibit coercive fields larger than any others reported for iron-based perovskites, have been analyzed at room temperature with the neutron powder diffraction technique and the Rietveld method of profile fitting. For x in the range 0.05–0.10 the material is monophasic with orthorhombic symmetry (space group Pnma), and crystallizes in the perovskite-like cell of LaFeO3, Fe/Cu cations occupy octahedral sites, La/Sr cations are twelve-fold coordinated. For x=0.20 the material is biphasic, with a main orthorhombic phase (space group Pnma) and a secondary rhombohedral phase with space group R-3c (hexagonal setting). The structural transition from the orthorhombic to the rhombohedral phase reduces the structural distortion of the (Fe/Cu)O6 octahedron. The average bond distance (Fe/Cu)–O and the pseudo-cubic unit cell volume decrease with increasing Cu content in accordance with the presence of higher valence states of the transition metals. The magnetic structure was modeled for the monophasic samples (x=0.05 and 0.10) assuming an antiferromagnetic interaction between Fe/Cu neighboring cations (G-type): the magnetic moments order antiferromagnetically along the b-axis, with the spin direction along a-axis. The magnetic moments of the Fe/Cu atoms are μx=2.66(3)μB and 2.43(3)μB for the compositions x=0.05 and 0.10, respectively. By measuring the first magnetization curve and the hysteresis loops, coexisting antiferromagnetic and weak ferromagnetic interactions were observed for all samples. Hysteresis loops measured at room temperature of the sample with x=0.05. [Display omitted] ► Iron based perovskites with the largest coercive fields. ► Sr and Cu lanthanum ferrites as magnetic materials. ► Doped lanthanum ferrites show antiferromagnetic and weak ferromagnetic interactions. ► Sr and Cu lanthanum ferrites show distorted perovkite structure.