CoFe(2)O(4) nanoparticles (D(NPD) ~6 nm), prepared by a thermal decomposition technique, have been investigated through the combined use of dc magnetization measurements, neutron diffraction, and (57)Fe Mössbauer spectrometry under high applied magnetic field. Despite the small particle size, the value of saturation magnetization at 300 K (M(s) ͠= 70 A m(2) kg(-1)) and at 5 K (M(s) ͠= 100 A m(2) kg(-1)) are rather close to the bulk values, making the samples prepared with this method attractive for biomedical applications. Neutron diffraction measurements indicate the typical ferrimagnetic structure of the ferrites, showing an inversion degree (γ(NPD) = 0.74) that is in very good agreement with cationic distribution established from low temperature (10 K) Mössbauer measurements in high magnetic field (γ(moss) = 0.76). In addition, the in-field Mössbauer spectrum shows the presence of a non-collinear spin structure in both A and B sublattices. The results allow us to explain the high value of saturation magnetization and provide a better insight into the complex interplay between cationic distribution and magnetic disorder in ferrimagnetic nanoparticles.

The nuclear and magnetic structures of Fe1+yTe1$-${}xSex (0$\le${}x$\le${}0.20) compounds was analyzed between 2 and 300 K by means of Rietveld refinement of neutron powder diffraction data. Samples with x$\le${}0.075 undergo a tetragonal to monoclinic phase transition at low temperature, whose critical temperature decreases with increasing Se content; this structural transition is strictly coupled to a long-range antiferromagnetic ordering at the Fe site. Both the transition to a monoclinic phase and the long-range antiferromagnetism are suppressed for 0.10$\le${}x$\le${}0.20. The onset of the structural and of the magnetic transition remains coincident with the increase in Se substitution. The low-temperature monoclinic crystal structure has been revised. Superconductivity arises for x$\ge${}0.05, therefore a significant region where superconductivity and long-range antiferromagnetism coexist is present in the pseudobinary FeTe-FeSe phase diagram.

We measure magnetotransport of F-doped SmFeAsO samples up to 28 T and we extract the upper critical fields, using different criteria. In order to circumvent the problem of criterion-dependent $H_{c2}$ values, we suggest a thermodynamic estimation of the upper critical field slope $d{H}_{c2}/dT$ based on the analysis of conductivity fluctuations in the critical regime. A high field slope as large as $-12\text{T}/\text{K}$ is thus extracted for the optimally doped sample. We find evidence of a two-dimensional lowest Landau level (LLL) scaling for applied fields larger than ${\mu }_0{H}_{\text{LLL}}\sim 8\text{T}$. Finally, we estimate the coherence length values and we observe that they progressively increase with decreasing $T_c$. In all cases, the coherence length values along the $c$ axis are smaller than the interplanar distance, confirming the two-dimensional nature of superconductivity in this compound.

In this work we present a systematic experimental and theoretical study of the structural, transport, and superconducting properties of $\text{Sm}\left({\text{Fe}}_{1-x}{\text{Ru}}_x\right)\text{As}\left({\text{O}}_{0.85}{\text{F}}_{0.15}\right)$ polycrystalline samples as a function of Ru content $\left(x\right)$ ranging from 0 to 1. The choice of Ru as isoelectronic substitution at Fe site of F-doped compounds allows to better clarify the role of structural disorder in modifying the normal and superconducting properties of these recently discovered multiband superconductors. Two different regions are identified: the Fe-rich phase $\left(x<0.5\right)$ where superconducting and normal-state properties are strongly affected by disorder induced by Ru substitution; the Ru-rich phase $\left(x>0.5\right)$ where the system is metallic and strongly compensated and the presence of Ru frustrates the magnetic moment on Fe ions. Here the lack of magnetic features and related spin fluctuations may be the cause for the suppression of superconductivity. DOI: http://dx.doi.org/10.1103/PhysRevB.81.184504 © 2010 The American Physical Society

Metal halide perovskites are one of the most investigated materials in optoelectronics, with their lead-based counterparts being renowned for their enhanced optoelectronic performance. The 3D CsPbX₃ structure has set the standard with many studies currently attempting to substitute lead with other metals while retaining the properties of this material. This effort has led to the fabrication of metal halides with lower dimensionality, wherein particular 2D layered perovskite structures have captured attention as inspiration for the next generation of colloidal semiconductors. Here we report the synthesis of the Ruddlesden–Popper Cs₂CdCl₄:Sb³⁺ phase as colloidal nanoplatelets (NPs) using a facile hot injection approach under atmospheric conditions. Through strict adjustment of the synthesis parameters with emphasis on the ligand ratio, we obtained NPs with a relatively uniform size and good morphological control. The particles were characterized through transmission electron microscopy, synchrotron X-ray diffraction, and pair distribution function analysis. The spectroscopic characterization revealed most strikingly an intense cyan emission under UV excitation with a measured PLQY of ∼20%. The emission was attributed to the Sb³⁺-doping within the structure.