Study of Soft/Hard Bimagnetic CoFe²/CoFe²O⁴ Nanocomposite.

We report an experimental study of the bimagnetic nanocomposites CoFe₂/CoFe₂O₄. The precursor material, CoFe₂O₄ was prepared using the conventional stoichiometric combustion method. The nano-structured material CoFe₂/CoFe₂O₄ was obtained by total oxygen reduction of CoFe₂O₄ using a thermal treatment at 350 °C in H₂ atmospheres following the partial oxidation in O₂ atmospheres at 380 °C during 120; 30; 15, 10, and 5 min.

Griffiths phase and spontaneous exchange bias in LaSrCoMnFeO.

LaSrCoMnFeO (LSCMFO) compound was prepared by solid state reaction and its structural, electronic and magnetic properties were investigated. The material forms in rhombohedral [Formula: see text] structure, and the presence of distinct magnetic interactions leads to the formation of a Griffiths phase above its FM transition temperature (150 K), possibly related to the nucleation of small short-ranged ferromagnetic clusters. At low temperatures, a spin glass-like phase emerges and the system exhibits both the conventional and the spontaneous exchange bias (EB) effects.

Shell-mediated control of surface chemistry of highly stoichiometric magnetite nanoparticles.

Magnetite (Fe3O4) nanoparticles are one of the most studied nanomaterials for different nanotechnological and biomedical applications. However, Fe3O4 nanomaterials gradually oxidize to maghemite (γ-Fe2O3) under conventional environmental conditions leading to changes in their functional properties that determine their performance in many applications. Here we propose a novel strategy to control the surface chemistry of monodisperse 12 nm magnetite nanoparticles by means of a 3 nm-thick Zn-ferrite epitaxial coating in core/shell nanostructures.

Magnetic interactions in the S = 1/2 square-lattice antiferromagnets BaCuTeO and BaCuWO: parent phases of a possible spin liquid.

The isostructural double perovskites BaCuTeO and BaCuWO are shown by theory and experiment to be frustrated square-lattice antiferromagnets with opposing dominant magnetic interactions. This is driven by differences in orbital hybridisation of Te and W. A spin-liquid-like ground state is predicted for BaCu(TeW)O solid solution similar to recent observations in SrCu(TeW)O.

Thermal Transport and Phonon Hydrodynamics in Strontium Titanate.

We present a study of thermal conductivity, κ, in undoped and doped strontium titanate in a wide temperature range (2-400 K) and detecting different regimes of heat flow. In undoped SrTiO_{3}, κ evolves faster than cubic with temperature below its peak and in a narrow temperature window. Such behavior, previously observed in a handful of solids, has been attributed to a Poiseuille flow of phonons, expected to arise when momentum-conserving scattering events outweigh momentum-degrading ones.

Spin-liquid-like state in a spin-1/2 square-lattice antiferromagnet perovskite induced by d-d cation mixing.

A quantum spin liquid state has long been predicted to arise in spin-1/2 Heisenberg square-lattice antiferromagnets at the boundary region between Néel (nearest-neighbor interaction dominates) and columnar (next-nearest-neighbor interaction dominates) antiferromagnetic order. However, there are no known compounds in this region. Here we use d-d cation mixing to tune the magnetic interactions on the square lattice while simultaneously introducing disorder.

Synthesis, characterization and magnetic properties of polymer-Fe3O4 nanocomposite.

The chemical stability of magnetic particles is of great importance for their applications in medicine and biotechnology. The most challenging problem in physics of disordered systems of magnetic nanoparticles is the investigation of their dynamic properties. The chemical coprecipitation process was used to synthesize spherical magnetite nanoparticles of 14 nm.

First-order phase transitions in CaFe₂As₂ single crystal: a local probe study.

(57)Fe Mössbauer spectroscopy has been used to investigate the structural and magnetic phase transitions of CaFe₂As₂ (T(N) = 173 K) single crystals. For this compound we found that V(ZZ) is positive and parallel to the c-axis of the tetragonal structure. For CaFe₂As₂ a magnetic hyperfine field B(hf) was observed at the (57)Fe nucleus below T(N) ~173 K.

Mössbauer study of superconducting NdFeAsO(0.88)F(0.12) and its parent compound NdFeAsO.

(57)Fe Mössbauer spectroscopy has been used to investigate the magnetic order of non-superconducting NdFeAsO (T(N) = 140 K) and superconducting NdFeAsO(0.88)F(0.12) (T(c) = 45 K).