Local environments of iron and cobalt in doped MgB₂superconductors

Abstract

MgB2 has been doped with 57Fe and 57Co in order to probe the electronic structure of the superconductor by Mössbauer spectroscopy. Simultaneous SEM–EDX studies showed that both Fe and Co were incorporated to some extent into the MgB2 host lattice. Mössbauer spectroscopy indicated that Fe2B and FeB were also formed during the preparation. At higher Fe contents Fe2B appeared unambiguously as a secondary phase in the x-ray diffraction. CoB was detected at substitution levels of 10 mol% and greater. Both Fe and Co doping decreased the Tc(0) modestly. Co and Fe were found to substitute at the Mg site in the MgB2 lattice. The Mössbauer parameters for 57Co and 57Fe were consistent with a metallic environment. The similarity of the isomer shifts in MgB2 and in cuprate superconductors is being discussed.

Synthesis and characterization of magnetic beads containing aminated fibrous surfaces for removal of Reactive Green 19 dye: kinetics and thermodynamic parameters

“…According to standard Mössbauer spectra22, 23 the presence of the sextet indicates ferromagnetic ordering in the sample which can be explained by super‐paramagnetic relaxation 24. The broad wings in the spectrum,25 and the central doublet come from the super paramagnetic behavior of the ferromagnetic nano‐particle within the beads. Kudnig and Bommel26 only obtained a central doublet with samples having particle size ∼18 nm or lower and attributed the doublet to a super paramagnetic state.…”

Metallurgical phases and their magnetism at the interface of nanoscale MgB2/Fe layered structures

“…Apparently, during annealing, the fraction of more slowly relaxing larger Fe-B nanoparticles and/or the fraction of magnetically ordered 57 Fe clusters in the MgB 2 matrix are dissolved by diffusion, leading to a more extended depth profile of diluted isolated paramagnetic 57 Fe atoms in the MgB 2 matrix. The latter state does not exhibit magnetic ordering at 5 K. Hence, we attribute the observed average isomer shifts of δ = 0.227 mm s −1 at RT and of δ = 0.336 mm s [20]), which were assigned to 57 Co and 57 Fe atoms that substitute Mg atoms in the MgB 2 lattice.…”

“…Phase analysis by Mössbauer spectroscopy is based on the similarity of the observed 57 Fe hyperfine parameters of the samples (hyperfine magnetic field, B hf , isomer shift, δ, quadrupole splitting, QS, and quadrupole nuclear level shift, ε) with the known parameters of bulk Fe-B phases. The possible phases that form in an MgB 2 -Fe powder system after solid state reaction were reported earlier [19,20]. According to these references, crystalline secondary phases of ferromagnetic Fe 2 B and FeB can form, and, moreover, Fe atoms can diffuse into the MgB 2 phase.…”

“…As indicated by the small positive isomer shift and significant quadrupole splitting, the clusters do not consist of pure Fe, but have partially reacted (at least at their interface) with B atoms of the MgB 2 films, forming the above mentioned superparamagnetic Fe-B phase. A small fraction of the deposited 57 Fe atoms very likely diffused (at an atomic level) into the MgB 2 layers during deposition [19,20], forming a paramagnetic state at both RT and 5 K, contributing strongly to the corresponding doublets. However, as the intensity oscillations up to fifth order in the small-angle XRD pattern ( figure 1(a)) prove, the multilayer structure is well developed, the MgB 2 / 57 Fe interfaces are fairly sharp, and diffusion is not severe in the as-prepared sample M1, and presumably also in the other as-prepared samples M2 and M3.…”

Fabrication of Alternately-layered MgB2/B Thin Films and Their Superconducting Properties

“…、Zr 16) 、Al 17,18) 等の金属、Co 19) 、Fe 19) 等の磁性体、 そしてSiC [20][21][22][23][24][25] Fig. 1 XRD spectra of alternately-layered MgB 2 /B thin films prepared by differing the thickness of MgB 2 -layers and the pure MgB 2 film.…”