Cluster superconductivity in the magnetoelectric Pb(Fe1/2Sb1/2)O3 ceramics

We report the observation of cluster (local) superconductivity in the magnetoelectric Pb(Fe1/2Sb1/2)O3 ceramics prepared at a hydrostatic pressure of 6 GPa and temperatures 1200-1800 K to stabilize the perovskite phase. The superconductivity is manifested by an abrupt drop of the magnetic susceptibility at the critical temperature TC 7 K. Both the magnitude of this drop and TC decrease with magnetic field increase. Similarly, the low-field paramagnetic absorption measured by EPR spectrometer drops significantly below TC as well. The observed effects and their critical magnetic field dependence are interpreted as manifestation of the superconductivity and Meissner effect in metallic Pb nanoclusters existing in the ceramics. Their volume fraction and average size were estimated as 0.1-0.2% and 140-150 nm, respectively. The superconductivity related effects disappear after oxidizing annealing of the ceramics.Comment: 9 pages, 5 figure

Stereotypes about aging population

First, the paper presents stereotypes about aging and its impact on the aging population. It is indisputable that these stereotypes, no matter whether they are positive or negative, have an influence on psychological as well as physical health. Second, the paper informs about memory training programme for seniors and the part of research focused on subjectively perceived changes in relevant aspects. Research findings are discussed in terms of possibilities to influence the stereotypes about the aging population

Hyperfine Fields and Lattice Deformations in Ba and Sr Hexaferrites

Hyperfine magnetic fields on ⁵⁷Fe nuclei in Sr and Ba hexagonal ferrites are calculated in dependence on unit cell volume and c/a ratio. By analysing the local deformations of Fe-O-Fe triads the results are explained as changes to contact hyperfine field due to Fe-O covalency effects and supertransferred hyperfine fields. Most pronounced effect is found for bipyramidal iron Fe(b) where the total contact field is reduced due to noticeable shortening of Fe(b)-O bonds

Study of Y-type Hexaferrite by Means of 57Fe\text{}^{57}Fe NMR and Electronic Structure Calculations

The electron structure and site preferences of Zn and Fe cations in Y hexaferrite system were calculated. The hyperfine magnetic fields on $\text{}^{57}Fe$ nuclei were determined using WIEN2k and corrections for hyperfine contact interaction. The calculated fields were compared to $\text{}^{57}Fe$ nuclear magnetic resonance (NMR) experiment in $Ba_2Zn_2Fe_{12}O_{22}$ single crystal with an aim of interpretation of experimental NMR spectrum

Structure of Iron Oxide Nanoparticles Studied by 57Fe\text{}^{57}Fe NMR

In this work we apply nuclear magnetic resonance (NMR) spectroscopy of $\text{}^{57}Fe$ nuclei for investigation of submicron and nanocrystalline iron oxide systems. The studied iron oxide particles are obtained from ferrous hydroxide gels (prepared from $FeCl_{2}$ and KOH) by aging at elevated temperatures (90 °C) with $KNO_{3}$ as oxidant. The $\text{}^{57}Fe$ NMR spectra of the samples are measured in temperature range 4.2-370 K in a zero external magnetic field. Signals of $\text{}^{57}Fe$ nuclei assigned to tetrahedral and octahedral iron sites are well resolved. The NMR spectra and their temperature dependences are compared with those of stoichiometric and nonstoichiometric magnetite single crystals, as well as with samples of maghemite

NMR Study of Multiferroic Iron Niobate Perovskites

We present $\text{}^{93}Nb$, $\text{}^{207}Pb$ and $\text{}^{135,137}Ba$ NMR study of multiferroic lead iron niobate and barium iron niobate ceramics. We ascribe development of NMR spectra on cooling below room temperature to magnetism of ferric ions close to resonating nuclei and introduce a framework capable of describing key features of the observed temperature induced changes. We show that the ferric ions have much stronger influence on hyperfine fields at nuclei of large cations in lead compound and estimate strength of interaction of superantiferromagnetic clusters