Critical Magnetic Field Hc2 Research Articles

Magnetization spiral structure and high domain wall velocity induced by inertial effect

In ultrafast magnetism, i.e., the short time scales such as picosecond and femtosecond, we report that the spiral structure of magnetization can be formed by the inertial effect. Comparing with the case of fast magnetism in nanosecond time scale, we can obtain a higher velocity of domain wall in ultrafast magnetism due to the driving of inertial moment. There is a critical value τc of angular momentum relaxation time τ for the inertial breakdown in uniaxial ferromagnet. Under the action of the inertial effect the domain wall width shows the characteristics of increases firstly as τ<τc, and then decreasing as τ>τc. It directly leads to the positive or negative mobility for the domain wall velocity as the inertia is less than or exceeds the critical value, respectively. In the high frequency mode (i.e., high field mode), we obtain the limit domain wall velocity, i.e., V→1/ατ. The smaller the inertia or damping, the faster the domain wall moves. For the case of biaxial anisotropic ferromagnets, the domain wall width and velocity decreases with the increasing inertia term, respectively. In the presence of inertia effect, there is an another critical magnetic field hc. The domain wall width decreases with the increase of the magnetic field as h<hc, while increases as h>hc. However, the domain wall velocity shows a nearly linear increase with the magnetic field. These results indicate that the ultrafast magnetism has more advantages than fast magnetism. It also provides a good control technique for rapid information processing in the future.

Magnetization Plateaus of a Double Fullerene Core/Shell Like-Nanostructure in an External Magnetic Field: Monte Carlo Study

Abstract: This paper concerns the investigation of the critical (HC) and the saturation (HS) magnetic fields behavior of the studied system as a function of different physical parameters. The Monte Carlo method is used to study the magnetic properties of the ferrimagnetic behavior of a double fullerene X60 core/shell-like nanostructure. Based on the Ising model, we focus our study on a system formed by a double sphere core/shell. The two spheres contain the spins  = ± 1/2 in the core surrounded by the spin S = ± 1, 0 in the shell. Various types of magnetization curves have been established, depending on the competition among the exchange couplings, the crystal fields, and the temperature. The study reveals that the saturation magnetic field (Hs) is significantly influenced by variations in all exchange coupling parameters, whereas the critical magnetic field (Hc) is only mildly affected by these parameter variations. Moreover, the crystal field and temperature both influence the critical and saturation magnetic fields. Keywords: Double fullerene core/shell-like structure, Magnetization plateaus, Monte Carlo simulations, Critical and saturation fields, External magnetic field.

THE STUDY ON TEMPERATURE-DEPENDENT SURFACE CRITICAL MAGNETIC FIELD OF IRON-BASED SUPERCONDUCTORS

The upper critical magnetic field (Hc2) is one of the important properties of superconductors in external magnetic field. The higher magnetic field strength, the more superconductivity is maintained. However, the surface critical magnetic field (Hc3) is larger than upper critical magnetic field which the ratio of Hc3 to Hc2 is constant. In this study, we investigated the surface critical magnetic field of the iron-based superconductor using Ginzburg-Landau’s anisotropic two-band method. The surface critical magnetic field was calculated with four temperature-dependent models. Our analytical formula of the surface critical magnetic field obtains the temperature parameters. Finally, the numerical calculation was applied to the experimental data of iron-based superconductors

Robust superconductivity and huge enhancement of upper critical field in Nb2CS2 MXene under high pressure

As a member of the emerging MXenes family, Nb2CS2 offers distinctive superconductivity, excellent electrical properties, and outstanding chemical stability, making it potentially useful for energy storage, medical imaging, and quantum computing. Herein, we systematically investigate how ultrahigh pressure affects the electrical properties of Nb2CS2. The results indicate that Nb2CS2 retains robust superconductivity with Tc&amp;gt;8 K up to the maximum applied pressure of 146.8 GPa. Moreover, the upper critical magnetic field Hc2(0) of Nb2CS2 increases with pressure, and the Pauli limit is violated at pressures greater than 120 GPa. Meanwhile, Hc2(0) increases to 19.3 T at 146.8 GPa, which is 4.8 times greater than at the initial pressure. Further analysis suggests that the significant enhancement of Hc2(0) below 30 GPa comes from the sharp pressure-induced rise of carrier concentration as the interlayer distance decreases, and the significant increase in Hc2(0) above 86 GPa may come from enhanced spin–orbit coupling or the possible unconventional superconducting pairing mechanisms. These results provide insights into the superconducting properties of MXene materials and offer guidelines for further research on electronic transport in Mxenes under ultrahigh pressure.

Large room-temperature magnetodielectric effect in polyvinylidene fluoride-trifluoroethylene/La0.7Sr0.3MnO[formula omitted] (0-3) nanocomposite thin films

We observe large room-temperature magnetodielectric effect (nearly 12% suppression of dielectric constant under ∼20 kOe field) as well as its remarkable field-driven switch – from positive to negative – in polyvinylidene fluoride-trifluoroethylene/La0.7Sr0.3MnO3 (PVDF-TrFE/LSMO) thin films (0–3 connectivity) containing 7.5 volume% LSMO. The magnetodielectric effect is mapped with the volume fraction of the LSMO nanoparticle across 5-20 volume%. It reveals a close correlation among the LSMO nanoparticles volume fraction, their distribution pattern within the PVDF-TrFE matrix, uniformity in the magnetic domain size (imaged by magnetic force microscopy), and the magnetodielectric effect. The observed 20% jump in the intrinsic bulk capacitance at a critical magnetic field HC∼10 kOe can be exploited to develop smart nanoscale magnetoelectric devices.

Search for superconductivity in hydrides of TiZrNb, TiZrNbHf and TiZrNbHfTa equimolar alloys

We have prepared and investigated the superconducting equimolar alloys TiZrNb, TiZrNbHf and TiZrNbHfTa, which exhibit transition temperatures Tc between 6.4 K and 8.4 K, and examined the influence of hydrogenation on their superconductivity. The upper critical magnetic field Hc2 of alloys was estimated to be above 10 T, in agreement with previous studies of superconducting alloys of similar composition. On the other hand, the hydrogenation of alloys, some of which appear to be promising for hydrogen storage, lead to suppression of superconductivity in TiZrNb, TiZrNbHf and TiZrNbHfTa dihydrides and in TiZrNbHfTa monohydride, and no transition to superconducting state was observed therein above 2 K. A possible reason for this may be related to the high concentration of disorder (defects) in hydrides originating from the preparation method during which the starting alloy disintegrates into fine powder.

Effect of Magnetic Impurities on Superconductivity in LaH10.

Polyhydrides are a novel class of superconducting materials with extremely high critical parameters, which is very promising for sensor applications. On the other hand, a complete experimental study of the best so far known superconductor, lanthanum superhydride LaH10 , encounters a serious complication because of the large upper critical magnetic field HC2 (0), exceeding 120-160T. It is found that partial replacement of La atoms by magnetic Nd atoms results in significant suppression of superconductivity in LaH10 : each at% of Nd causes a decrease in TC by 10-11K, helping to control the critical parameters of this compound. Strong pulsed magnetic fields up to 68T are used to study the Hall effect, magnetoresistance, and the magnetic phase diagram of ternary metal polyhydrides for the first time. Surprisingly, (La,Nd)H10 demonstrates completely linear HC2 (T)∝|T -TC |, which calls into question the applicability of the Werthamer-Helfand-Hohenberg model for polyhydrides. The suppression of superconductivity in LaH10 by magnetic Nd atoms and the robustness of TC with respect to nonmagnetic impurities (e.g., Y, Al, C) under Anderson's theorem gives new experimental evidence of the isotropic (s-wave) character of conventional electron-phonon pairing in lanthanum decahydride.

Study of RHQT-processed Nb3Al multifilamentary rectangular tape strand to be applied to a fusion magnet

Nb3Al superconducting wire shows an excellent strain tolerance compared with Nb3Sn wire and is promising conductor for a future fusion magnet. We investigated about the changes of the superconducting property and the wire flexibility by rectangular tape-shaped deformation on the Rapid Heating/Quenching and Transformation (RHQT) processed Nb3Al multifilamenatry wires. The improvement of the wire flexibility will be enable to the future complicated coil winding through the "React and Winding" process. The Rapid Heating/Quenching (RHQ) treatment was performed on a round-shaped Nb/Al precursor wire, and Nb/Al filaments has converted to the ductile bcc Nb-Al supersaturated solid solution (bcc-SS) phase after the RHQ (Rapid heating and quenching) treatment. The round-shaped wire after the RHQ treatment could be easily cold flat-rolled to the rectangular tape-shape (width: 4.6 mm, thickness: 0.2 mm) at room temperature. The phase transformation from bcc-SS phase to stoichiometric A15-Nb3Al phase by the post-annealing was confirmed. Critical current (Ic) and critical current density (Jc) at 4.2 K and 18 T of the RHQT processed Nb3Al rectangular tape strand was obtained approximately 180 A and 200 A/mm2, respectively. Jc property above 18 T in the rectangular tape strand were clearly improved compared to the round wire strand, and the upper critical magnetic field (Hc2) above 26 T was also obtained. In addition, no Ic deterioration by applying a bending strain up to 0.66% was observed. The wire flexibility of the RHQT processed Nb3Al strand could be improved by the change of wire shape from round wire to rectangular tape. We found that the Nb3Al rectangular tape stand will be desirable and suitable material to apply to a future huge fusion magnet through the React & Winding process.

Enhancement of critical current density and strong vortex pinning in high entropy alloy superconductor Ta[formula omitted]Nb[formula omitted]Hf[formula omitted]Zr[formula omitted]Ti[formula omitted] synthesized by spark plasma sintering

We synthesized the high entropy alloy (HEA) Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6 compound by planetary ball milling and the spark plasma sintering (SPS) method. The sintered HEA sample had a BCC crystal structure with small amount of secondary phases. The superconducting phase transition is observed in the electrical resistivity (Tc∼ 7.8 K) and magnetic susceptibility (Tc∼ 7.6 K) measurements, and the Tc was similar to that of an arc-melted sample. The zero-temperature limit of the upper critical magnetic fields Hc2(0)= 10.5 T and coherence length ξ = 5.66 nm were slightly decreased or comparable to the arc-melted HEA sample (Hc2(0)= 12.05 T and ξ= 5.23 nm). The field-dependent isothermal magnetization hysteresis M(H) exhibited the typical type- 2 superconducting behavior with magnetic flux avalanches in the low magnetic field region. The calculated critical current densities were significantly increased by 286 % (Jc= 32,606 A cm−2 at 2 K) ∼ 687 % (Jc= 73,200 A cm−2 at 4 K) compared to the arc-melted HEA sample (Jc= 11,401 A cm−2 at T= 2 K). The enhanced Jc of the sintered HEA sample is caused by enhancement of the pinning force due to point pinning as well as surface pinning effects. The vortex relaxation measurements showed stable remanent magnetization for over 10,000 s after magnetic fields were turned off, which is unlike conventional sueprconducting vortex relaxation behavior. The strong pinning force in the SPS sintered Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6 compound is beneficial for practical applications because of the significantly enhanced critical current density Jc with stable remanent magnetization Mrem(t).

Role of Y substitution for Ca-site on magneto-resistivity properties of Bi-2212 superconductor rods prepared by LFZ

This comprehensive study delves into the effect of partial Y3+ substitution for Ca2+ in Bi2Sr2CaCu2O8+y superconducting rods prepared by the laser floating zone method (LFZ). The critical transition temperatures (Tconset, Tc, Tcoffset), activation energy (U), irreversibility field (Hirr), upper critical magnetic field (Hc2), coherence length (ξ), and penetration depth (λ) are determined by means of magneto-resistivity measurements performed between 0 and 5 T. According to the resistivity-temperature graph for zero fields, Tcoffset values tend to decrease regularly from 90.8 K to 87.1 K, and the residual resistivity values increase steadily from 0.14 to 9.7 mΩ .cm with the Y-content. The change of these two parameters is a sign that Y-introduction into the Bi-2212 matrix undermines the inter-grain coupling and increases the level of permanent-defects in the crystalline structure. However, the relatively high Tcoffset values and extremely low residual resistivity, especially in the pure and low Y-substituted samples, reflect the success of the LFZ process in growing homogeneous and well-oriented Bi-2212 grains. The resistivity transition broadening is observed when the applied field increases and Tcoffset values decrease dramatically, i.e. from 90.8 K to 72.1 K for the pure sample and from 87.1 K to 48.2 K for the 0.20Y-substituted ones. The calculated U values using the TAFF model decrease with the increase of the Y-content and the magnetic field. In addition, the magnetic field and temperature dependence of U is expressed by using U(H,T) ∼ ΔT H−η equation. Deduced parameters of Hirr and Hc2 from magneto-resistivity curves and theoretical findings of ξ and λ also favor the degradation of U values with the augmentation of Y-content in the Bi-2212 rods.

Dynamics of fractional vortices in two-band superconductors

The entry of fractional vortices and their subsequent dynamics inside a two-band superconductor is explored based on the numerical solutions of time-dependent Ginzburg–Landau (TDGL) equations. We consider the case when superfluid electron condensates from two zones are characterized by quite different parameters, such as coherence lengths ξi, and London penetration depths λi, which in turn leads to the different critical magnetic fields Hc,iand fractional flux quanta ϕivalues for the superconducting state in these two zones. Numerical solutions of TDGL equations in increasing external magnetic field followed by mathematical modeling of magnetic flux penetration were performed for this case by finite element method. We have explored the time evolution for the fractional vortices penetration process and their subsequent dynamics inside the specimens for two geometries: the circular disk, and the circular disk with a triangular cutout. Obtained results indicate that magnetic flux penetrates inside the specimen in the form of fractional vortices when they can overcome the edge barrier, which may be different for these two vortex types. Therefore, in increasing external magnetic field first penetrate vortices with a lower barrier height (i.e., lower Hc,i) while the other type of fractional vortices start their penetration at higher external field value. Another mechanism for the formation of fractional vortices during their entrance in a two-band superconductor is related to the difference in their flux values and viscosity coefficients which determine the rate of vortex proliferation inside the sample. Within the specimen, fractional vortices move in order to arrange. Vortices of different types attract to each other and try to stick together thus forming composite vortices with the whole flux quantum value ϕ0 = h/2e.

The activation energy U(T,B) in high temperature superconductor

It is reported in this paper on the thermally assisted flux flow in epitaxial YBa2Cu3O7-δ deposited by Laser ablation method on the SrTiO3 substrate. The resistivity measurements ρ (T, B) of the sample under various values of the magnetic field up to 14T in directions B∥ab-plane and B∥c-axis with a dc weak transport current density were investigated in order to determine the activation energy and then understand the vortex dynamic phenomena and therefore deduce the vortex phase diagram of this material. The apparent activation energy U0 (B) calculated using an Arrhenius relation. The measured results of the resistivity were then adjusted to the modified thermally assisted flux flow model in order to account for the temperature-field dependence of the activation energy U (T, B). The obtained values from the thermally assisted activation energy, exhibit a behavior similar to the one showed with the Arrhenius model, albeit larger than the apparent activation energy with ∼1.5 order on magnitude for both cases of the magnetic field directions. The vortex glass model was also used to obtain the vortex-glass transition temperature from the linear fitting of [d ln ρ/dT ] −1 plots. In the course of this work thanks to the resistivity measurements the upper critical magnetic field Hc2 (T), the irreversibility line Hirr (T) and the crossover field HCrossOver (T) were located. These three parameters allowed us to establish a phase diagram of the studied material where limits of each vortex phase are sketched in order to optimize its applicability as a practical high temperature superconductor used for diverse purposes.

The magnetic switch manufacturing by using ferrofluid and ferrofluid doped copper nanoparticles

In this work, a magnetic switch was prepared using two typesof ferrofluid materials, the pure ferrofluid and ferrofluid doped with copper nanoparticles (10 nm). The critical magnetic field (Hc) and the state of magnetic saturation (Hs) were studied using three types of laser sources. The main parameters of the magnetic switch measured using pure ferrofluid and He-Ne Laser source were Hc(0.5 mv, 0.4 G), Hs (8.5 mv, 3 G). For the ferrofluid doped with copper nanoparticles were Hc (1 mv, 4 G), Hs (15 mv, 9.6 G), Using green semiconductor laser for the Pure ferrofluid were Hc (0.5 mv, 0.3 G) Hs (15 mv, 2.9 G). While the ferrofluid doped with copper nanoparticles were Hc (0.5 mv, 1 G), Hs (12 mv, 2.8 G) and by using the violet semiconductor laser the pure ferrofluid parameters were Hc(0.5 mv, 0.5 G), Hs (15 mv, 3.5 G) while the ferrofluid doped with coppernanoparticles are Hc (0.5 mv,1 G), Hs (15 mv, 3.3 G).

Effect Melting Time on the Excess Conductivity and Critical Parameters of BSCCO Cooper Oxide System

We report here the effect of melting time (tm = 2.5–4.5 min) on the conductivity and dimensionality of BSCCO cooper oxide system. It is found that the mean field and crossover temperatures (Tcmf, T01, and T02) are increased by increasing tm up to 3.5 min, followed by a decrease with further increase of tm up to 4.5 min. The logarithmic plots of excess conductivity (∆σ) and reduced temperature (Є) reveal three regions of different exponents corresponding to two crossover temperatures in the slope of each plot. Interestingly, the crossover occurs from three dimensional (3D) to zero dimensional (0D/SW) in the mean field region and from 0D/SW to two dimensional (2D) in the critical field region, for the samples melted at tm = 2.5, 4, and 4.5 min, while it occurs from (3D) to one dimensional (1D) and from (1D) to (2D) for the sample melted at tm = 3.5 min. On the other hand, we have estimated several physical parameters such as order parameter exponents (λ), interlayer coupling (K), c-axis coherence length (ξc (0)), anisotropy (γ), Ginsburg number (Gi), critical magnetic fields (Hc(0), Hc1(0), and Hc2(0)), and critical current (Jc (0)) for all samples. It is found that λ1, λ3, K, ξc (0), Gi, and γ are increased by increasing tm up to 3.5 min, followed by a decrease with further increase of tm up to 4.5 min as well as Tc, Tcmf, and T0 behaviors. But the vice is versa for the behaviors of λ2, κ, Hc(0), Hc1(0), Hc2(0), Jc(0), and NG. Moreover, it is observed that the behavior of critical fields and critical current against melting time is controlled by the order parameter exponent of the second region rather than the first and third regions. These results are discussed in terms of the correlation between the effects of melting time on the weak links and the flow of actual supercurrent in the considered system.

Superconductivity in the Electron-Doped Chevrel Phase Compound Mo6S6.8Te1.2.

Chevrel-phase superconducting compounds AyMo6Q8 (A = Pb, Mg, etc. and Q = S, Se, Te) have attracted much attention due to their ultrahigh upper critical magnetic fields (Hc2). However, the binary compounds Mo6S8 and Mo6Te8 show no superconducting properties above 2 K. In this work, the new Chevrel-phase pseudobinary compound Mo6S6.8Te1.2 with a superconducting transition temperature (Tc) of 3.6 K was successfully synthesized by a two-step process. A detailed investigation implies that the superconductivity in Mo6S6.8Te1.2 may derive from the increased electronic density near the Fermi level in comparison to Mo6S8. Our work provides a feasible scheme to search for new superconducting compounds.

Unusual magnetic phenomena in dynamic torsion studies of fullerene Rb3C60

In dynamic experiments using a highly sensitive torsion technique, the magnetic properties of the doped Rb3C60 single crystal are studied over a wide temperature range. The critical temperature of the superconducting transition Tc, the critical magnetic field Hc1, the pinning forces of both the Abrikosov vortices and the magnetic moments of dipoles at T >> Tc, at which relaxation processes are important, are determined and investigated. It was shown that the structural transition Fm3m-Pa3 at T = 260 K is accompanied by a reformation of the magnetic structure. Both the usual peaks at T ∼ 160–250 K and the not quite ordinary peaks of gigantic absorption of the energy of the oscillations, which shift to room temperature over time, were observed. The phenomenon is discussed in the framework of the cooperative Jahn-Teller effect, taking into account possible orbital and spin ordering. The relaxation processes at room temperatures (T ∼ 300 K) were studied. After many days of exposure (annealing) of fullerene at T ≥ 40 °C, in experiments with cooling from room temperatures, phenomena typical for a superconducting transition with giant pinning and damped oscillations were observed at T ∼ 200 K. The results of studies of magnetic phase transitions at T = 180–200 K in pure fullerite C60 (99.98% Term. Sublimed), which are related to the detected unusual magnetic phenomena in fullerene Rb3C60, are presented.

Quantum Griffiths singularities in TiO superconducting thin films with insulating normal states

A superconductor–metal transition (SMT) with an unconventional diverging dynamic critical exponent was recently discovered, and it drew tremendous attention because this signature of a quantum Griffiths singularity (QGS) was thought to be a common characteristic of low-disorder crystalline superconductors. However, because the QGS was observed only in limited materials with metallic normal states, the question of whether the QGS exists in other superconducting systems is still unanswered. In this paper, a superconductor–insulator transition (SIT) is observed in TiO thin films with insulating normal states, which offers a more universal platform for investigating the QGS. A thickness-tuned SIT is obtained when the magnetic field is zero. Importantly, a magnetic field-tuned SIT with a diverging dynamic critical exponent, which is direct evidence of a QGS, is observed in TiO thin films with different thicknesses. By constructing a comprehensive phase diagram, it is demonstrated that the critical magnetic field Hc tends to saturate as the temperature approaches 0 K, which is different from the upturn trend of Hc observed in SMT systems and probably due to the weaker Josephson coupling of the locally ordered superconducting islands (rare regions) in a weakly insulating normal state background. The results extend the QGS scenario from only SMT systems to SIT systems, and they provide vital evidence that QGSs are common in crystalline superconducting thin films, which has possible applications in quantum-computing devices.

Weak or Strong Anisotropy in Fe(Se,Te) Superconducting Thin Films Made of Layered Iron-Based Material?

We study the temperature dependence of the upper critical magnetic field Hc2 in a layered iron-based superconducting (IBS) material of the 11-family, namely the Fe(Se,Te) thin film grown on CaF2 substrate. On the basis of intrinsic anisotropy as well as system dimensionality, it turns useful to make a comparison with an ultrathin film conventional low temperature superconductors (LTS) such as NbN, mostly used for device applications. We compare the anisotropy factors as a function of temperature and magnetic field. Both materials present a peculiar behavior: The LTS behaves as a strong anisotropic system, whereas the IBS shows very weak anisotropic features. The strong NbN character can be directly ascribed to the dimensionality of the ultrathin film employed, thus revealing a geometry effect. The weak Fe(Se,Te) trend should be related to its layered crystallographic structure, thus probing an intrinsic origin of its anisotropy. These characteristics become relevant for the potential application of this material in coated conductor technology.

Temperature Dependence of the Critical Field of the Organic Superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br

We present upper critical magnetic fields data for κ(BEDT-TTF)2Cu[N(CN)2]Br (hereafter k-Br), single crystals with the magnetic field applied either or perpendicular and parallel to the conducting layers. The H-T phase diagram in these single crystals has been deduced from tunnel diode oscillator-based contactless measurements in pulsed magnetic fields up to 56 T for the inter-plane (H ∥ b) and in-plane (H ∥ ac) field directions. Temperature dependence of the magnetic penetration depth in DC fields is also reported. The temperature dependence of the upper critical magnetic field Hc2(T) is not accounted for the Werthamer-Helfand-Hohenberg model for in-plane configuration. For the inter-plane orientation, a significant upward curvature is observed as the temperature decreases, in the range close to Tc, followed by saturation at lower temperatures. Possibly, this upturn is an indication of flux-line lattice melting.

Low-Temperature Magnetic Properties of Superconducting Indium Nanocomposites in Opal Matrix

We studied magnetic properties of the In–opal nanocomposite, which is a close-packed system of SiO2 spheres of the same diameter D with metal-filled cavities (series of opal structures with D = 190, 230, and 290 nm were studied). The dependencies of the samples’ magnetization m on temperature T, as well as on external magnetic field H, were measured at various temperatures below the critical temperature Tc of the superconducting (SC) transition. The critical temperature Tc and the critical magnetic field Hc were measured. Magnetization jumps were observed in m(H) dependences at temperatures below 2.6 K. It was found that the jumps are quasiperiodic as functions of H, and the number of jumps increases both with increase in the sweeping rate dH/dt, as well as with decrease in the characteristic size of the In inclusions in the nanocomposite. A model describing the breakup of the SC state with an increase in the external magnetic field is proposed. According to this model, when the screening current reaches a critical value in the near-surface layer of the nanocomposite, an avalanche-like penetration of the field into the volume of the nanocomposite occurs. After this, the SC state is restored, and the magnetic field “freezes” in the structure of the nanocomposite.