Vortex pinning and critical currents in nanostructured novel superconductors

A systematic analysis of the parameters associated with vortex pinning in novel superconductors containing nano-scale strong isotropic pinning centres (such as U/n processed Bi2223/Ag tapes and nanoparticle added MgB_2) has been carried out. Although the systems studied are very different as regards their structures, types of nano-scale defects and vortices, their pinning parameters (irreversibility fields and the fields for the maximum volume pinning force) show distinct common features. In particular, for moderate defect densities nϕ, in all these systems the enhancement of the pinning parameters in nanostructured state is approximately linear in nϕ over sizable field and temperature windows. Accordingly, these systems exhibit a kind of matching effects with the effective matching field Bϕ, correlated with the areal density of defects. The field Bϕ forms a natural field scale for the vortex pinning phenomena in such systems. However, at fields far from Bϕ, an interplay of different pinning mechanisms sets in. The impact of these results for the future enhancement of the flux pinning and critical currents in nanostructured Bi2223 and MgB_2 superconductors is briefly discussed

Properties and atomic structure of amorphous zirconium

Wide glass-forming range in Zr-M alloys (M = late transition metal) combined with a simple, often linear, variation of their physical properties with composition makes it possible to deduce physical properties of pure amorphous zirconium. We explore this possibility by using our experimental results for the magnetic susceptibility and superconducting transition temperature of paramagnetic amorphous Zr – (Co,Ni,Cu) alloys extending over a wide composition range. By combining these results with the literature results for the low temperature specific heat of the same alloy systems, we obtained a set of parameters associated with the electronic structure of the amorphous Zr. The comparison of these parameters with the results of the electronic structure calculations for different crystalline phases of Zr and with the results of the atomic structure and initial crystallisation studies of the same alloy systems indicate a fcc-like local atomic structure for amorphous Zr

Electronic and magnetic properties of ternary Zr2(Ni1-xMx)1 glassy alloys

The electric resistivities (in the temperature range from 8 K to 300 K), the room temperature magnetic susceptibility and the superconducting transition temperature of the amorphous Zr_2(Ni_1-xMx)_1 alloys (M=Ti, V, Cr, Mn, Fe, Co, Ni and Cu) have been investigated. The temperature dependence of the electrical resistivity can be described in terms of the incipient electron localisation effects inherent to the high resistivity alloys, same as of the other Zr-3d glassy alloys (3d=Fe, Co, Cu or Ni). The new features introduced with M are the pronounced nonmonotonic variations of the magnetic and electron-transport properties with M. The origin of these variations are the systematic changes in the electronic band structure of the alloys on going from M=Cu towards M=Ti (as confirmed by the photoemission experiments on similar (Zr_67Ni_33)_85M_15 amorphous alloys) and the tendency to the formation of localized magnetic moments for M around the middle of 3d-series (M=V, Cr, Mn and Fe). A novel feature is a rather strong suppression of the effects of the incipient localization in the resistivity by the magnetic interactions

Svojstva i atomska struktura amorfnog cirkonija

Wide glass-forming range in Zr-M alloys (M = late transition metal) combined with a simple, often linear, variation of their physical properties with composition makes it possible to deduce physical properties of pure amorphous zirconium. We explore this possibility by using our experimental results for the magnetic susceptibility and superconducting transition temperature of paramagnetic amorphous Zr – (Co,Ni,Cu) alloys extending over a wide composition range. By combining these results with the literature results for the low temperature specific heat of the same alloy systems, we obtained a set of parameters associated with the electronic structure of the amorphous Zr. The comparison of these parameters with the results of the electronic structure calculations for different crystalline phases of Zr and with the results of the atomic structure and initial crystallisation studies of the same alloy systems indicate a fcc-like local atomic structure for amorphous Zr.Siroko područje koncentracija za dobivanje staklastih Zr-M slitina (M = kasni prijelazni metal) u svezi s jednostavnim, često linearnim, promjenama fizičkih svojstava sa sastavom omogućuje određivanje fizičkih svojstava čistog amorfnog cirkonija. To smo istraživali rabeći naše eksperimentalne rezultate za magnetsku susceptibilnost i temperature supravodljivog prijelaza za paramagnetske amorfne Zr-(Co,Ni,Cu) slitine u širokom području koncentracija. Povezujući te rezultate s podacima iz literature za specifični toplinski kapacitet na niskim temperaturama za te slitine, dobili smo skup parametara pridruženih elektronskoj strukturi amorfnog cirkonija. Usporedba tih parametara s rezultatima računa elektronske strukture za različite kristalne faze Zr, te rezultatima studija atomske strukture i početne kristalizacije tih slitina, ukazuje na atomsku strukturu sličnu fcc za amorfni Zr

Comment on: High Mixing Entropy Enhanced Energy States in Metallic Glasses

A recent paper by Juntao Huo et al [Chin. Phys. Lett. 39 (2022) 0464011] reported a correlation between the entropy of mixing (and the corresponding energy state) and the thermal stability and mechanical parameters, for three Zr-Ti-Cu-Ni-Be metallic glasses (MG) including a high-entropy one (HEMG). The authors dismissed a possible compositional contribution to the variations of the thermal stability and mechanical parameters studied.Comment: 2 pages, 1 figur

Zapinjanje magnetskih vrtloga i kritične struje u novim nanostrukturiranim supravodičima

A systematic analysis of the parameters associated with vortex pinning in novel superconductors containing nano-scale strong isotropic pinning centres (such as U/n processed Bi2223/Ag tapes and nanoparticle added MgB2) has been carried out. Although the systems studied are very different as regards their structures, types of nano-scale defects and vortices, their pinning parameters (irreversibility fields and the fields for the maximum volume pinning force) show distinct common features. In particular, for moderate defect densities nφ, in all these systems the enhancement of the pinning parameters in nanostructured state is approximately linear in nφ over sizable field and temperature windows. Accordingly, these systems exhibit a kind of matching effects with the effective matching field Bφ, correlated with the areal density of defects. The field Bφ forms a natural field scale for the vortex pinning phenomena in such systems. However, at fields far from Bφ, an interplay of different pinning mechanisms sets in. The impact of these results for the future enhancement of the flux pinning and critical currents in nanostructured Bi2223 and MgB2 superconductors is briefly discussed.Predstavljamo sustavnu analizu parametara zapinjanja magnetskih vrtloga u novim supravodičima koji sadrže jake izotropne nanoskopske centre zapinjanja kao što su Bi2223/Ag trake obrađene sa U/n i MgB2 punjen nanočesticama silicija. Iako su ti materijali vrlo različiti u pogledu kristalne strukture, prirode vrtloga i nanoskopskih defekata, njihovi parametri zapinjanja vrtloga (ireverzibilna polja i polja maksimalne volumne sile zapinjanja) pokazuju izrazito slična svojstva. Npr., u tim je materijalima pojačanje zapinjanja vrtloga pri umjerenim gustoćama defekata nφ približno linearno s nφ u širokom području temperatura i magnetskih polja. Ukratko, ti materijali pokazuju učinke usklađivanja s efektivnim poljima usklađivanja Bφ razmjernim nφ. Polje Bφ čini prirodnu ljestvicu polja za zapinjanje vrtloga u takvim sustavima. Medutim, u poljima daleko od Bφ dolazi do miješanja različitih mehanizama zapinjanja vrtloga. Sažeto se razmatra utjecaj ovih saznanja na buduće pojačanje zapinjanja vrtloga u nanostrukturiranim Bi2223 i MgB2 supravodičima