Flux pinning and the paramagnetic Meissner effect in MgB₂with TiO₂inclusions

Abstract

The mixed-state superconducting properties of bulk MgB2+2 at.%TiO2, prepared by the in situ solid state reaction, have been investigated. The high-resolution transmission electron microscopy study reveals that the sample has combined microstructures, consisting of regions with small- and large-size MgB2 grains, and the MgO inclusions. The particular grains are separated by thin TiB2 interlayers along the c axis. Analysis on the mixed-state parameters, such as the upper critical field, the coherence length and the Ginzburg–Landau parameter κ, proves that the MgB2+2 at.% TiO2 belongs to a high-κ type-II superconductor in the dirty limit. The non-uniformly scaled microstructure results in an unusual (close to the double peak) magnetic field dependence of the pinning force density. The field-cooled temperature dependence of magnetic moment exhibits a transition of the sample to the paramagnetic state at certain applied magnetic fields, which is treated as a manifestation of the paramagnetic Meissner effect. The experimental results are discussed on the basis of modern theoretical approaches.

High field paramagnetic effect in the superconducting state of Ti0.8V0.2alloy

“…When this bulk current exceeds the diamagnetic surface current in the superconductor, the resultant magnetic response becomes paramagnetic. Few superconducting samples, however, exhibit such an effect in the mixed state in the presence of applied fields which can be as high as a few tesla [14][15][16][17][18][19][20][21]. This effect is called the high field paramagnetic effect (HFPME).…”

“…This effect is characterized by the lower values of magnetization obtained while cooling down in the presence of field than that in the field cooled warming measurements. An inhomogeneous flux distribution is considered to be the reason behind this observation at relatively high magnetic fields [18][19][20]. The inhomogeneous flux distribution can be caused by various reasons such as (a) inhomogeneous cooling of the sample [12], (b) surface superconductivity with a higher T C as compared to that of the bulk [12] (c) anisotropy in the upper critical field in the case of a polycrystalline sample [19] and/or (d) inhomogeneous distribution of pinning centers [18].…”

Superconductors for Large-Scale Applications

“…The investigation reveals that at certain temperature and magnetic field value, the magnetic field lines do not penetrate inside the superconductors and referred as Meissner effect (shown in Fig. 1) [13]. This phenomenon concludes that superconductors are diamagnetic with almost zero resistivity.…”

Strong paramagnetic response in Y containing V$_{0.6}$Ti$_{0.4}$ superconductor

“…Such behavior is also observed in many other superconductors such as Mo-Re 9 ,YBa 2 Cu 3 O 7−δ [10][11][12] , Nb thin films 13 and is known as high field paramagnetic Meissner effect (HFPME). In some cases, the paramagnetic response is so large that, the field cooled (FC) magnetisation value is higher than the normal state magnetisation 13,14 . Relaxation of magnetisation towards more positive values is also a characteristic feature of HFPME 7,10,13 .…”