Vladislav Kalitka

Magnetocaloric properties of manganites in alternating magnetic fields

The magnetocaloric effect has been measured in manganites of various chemical compositions in weak alternating magnetic fields. The capabilities of a simple method for measuring the magnetocaloric effect by modulating the magnetic field have been demonstrated. The dependence of the magnetocaloric effect on the temperature, magnetic field, and chemical composition of samples is interpreted.

Customised 2G HTS wire for applications

Reproducibility of superconducting properties and suitability for specific applications by means of customised finish are two important attributes required from commercial 2G HTS wire. This paper reviews the consistent performance of SuperOx production 2G HTS wire and describes two novel customisation options: surround polyimide varnish insulation and composite bulk materials assembled with 2G HTS wires soldered together.

Pulsed-Field Magnetization of Superconducting Tape Stacks for Motor Applications

The potential of (RE)BCO superconducting bulks in rotating machine designs has been explored through numerous experimental prototypes, with the bulks being magnetized to act as held poles. However, stacks of superconducting tapes have emerged as a promising alternative for trapped held magnets partly because of their suitability for the pulsed-field method of magnetization, which is considered the most practical method of trapping flux. The benefits of using a stack of tapes as rotor held poles suitable for motors are reported. The ability to have a long rectangular stack allows for motor designs with more efficient held poles in terms of the flux produced per unit area of the pole and easy scalability. Such a rectangular stack was experimentally magnetized for the first time using a race-track-shaped pulsed-held coil giving a highly uniform and well-defined trapped held. The unique self-supporting 120 mm by 12 mm stack was produced by compressing a high-temperature-superconducting tape coated with a thin layer of solder. Shorter rectangular stacks were pulse magnetized over a temperature range of 10-77 K using a fully automated pulsed magnetization system.

The effect of stabilizer on the trapped field of stacks of superconducting tape magnetized by a pulsed field

Stacks of high temperature superconducting tape, magnetized using pulsed fields, provide a new type of permanent magnet using superconductors. To optimize the trapped field in such stacks, the role of stabilization layers was investigated by pulse magnetizing a 12 mm square stack of 15 tape layers over a temperature range of 15-77 K. The stacks consisted of commercial tape with a silver stabilizer of 1-3 mu m or tape with an additional 20 mu m layer of copper on top of 1 mu m of silver. It was found that the trapped field and flux are relatively insensitive to the stabilizer thickness, and 1 mu m of silver only, led to the highest trapped field. An FEM model was also developed for a stack that considered for the first time both the actual thickness of metallic and superconducting layers, to investigate the effect of heating and heat transfer when a stack of tapes is magnetized.

Magnetic levitation using high temperature superconducting pancake coils as composite bulk cylinders

Stacks of superconducting tape can be used as composite bulk superconductors for both trapped field magnets and for magnetic levitation. Little previous work has been done on quantifying the levitation force behavior between stacks of tape and permanent magnets. This paper reports the axial levitation force properties of superconducting tape wound into pancake coils to act as a composite bulk cylinder, showing that similar stable forces to those expected from a uniform bulk cylinder are possible. Force creep was also measured and simulated for the system. The geometry tested is a possible candidate for a rotary superconducting bearing. Detailed finite element modeling in COMSOL Multiphysics was also performed including a full critical state model for induced currents, with temperature and field dependent properties and 3D levitation force models. This work represents one of the most complete levitation force modeling frameworks yet reported using the H-formulation and helps explain why the coil-like stacks of tape are able to sustain levitation forces. The flexibility of geometry and consistency of superconducting properties offered by stacks of tapes, make them attractive for superconducting levitation applications.

Self-Supporting Stacks of Commercial Superconducting Tape Trapping Fields up to 1.6 T Using Pulsed Field Magnetization

(RE)Ba2Cu3O7-δ bulks are well known for their ability to trap high magnetic fields; however, it has been recently shown by the current authors that stacks of commercial YBCOcoated conductor tape can outperform YBCO bulks of similar size at temperatures below 60 K due to their superior thermal stability during multipulse magnetization. The latest progress in a comprehensive study being undertaken to optimize and tailor the stacks for applications will be discussed. In this paper, a method of binding layers of superconducting tape is reported, namely, soldering of Pb-Sn solder-coated high-temperature superconducting tape developed by SuperOx. The performance of tape before and after the soldering procedure is discussed, and a 100-layer stack, trapping a field of up to 1.6 T above the surface after pulse magnetization at 10 K, is reported.

Direct and inverse magnetocaloric effects in A-site ordered PrBaMn2O6 manganite

Abstract The magnetocaloric effect (MCE) of A-site ordered PrBaMn2O6 manganite has been studied by direct methods and by the specific heat measurements. Direct measurements of the MCE in low magnetic fields were performed using recently proposed modulation technique and by classic direct method in high fields. Direct and inverse MCE are observed at Curie and Neel points correspondingly. A value of the inverse MCE in the heating run is less than in the cooling regime. This effect can be attributed to competition between ferromagnetic and antiferromagnetic interactions. Indirectly estimated and direct MCE values considerably differ around first order AF transition.

Magnetocaloric properties of La0.7Ca0.3MnO3 manganites with 16O → 18O isotopic substitution

This paper reports on a study of the effect of isotopic 16O → 18O oxygen substitution on the heat capacity and magnetocaloric properties of the La0.7Ca0.3MnO3 manganite. Direct measurements of the magnetocaloric effect have demonstrated that, in La0.7Ca0.3MnO3, the effect reaches a fairly large magnitude, but its temperature width is rather small. The 16O ar 18O isotopic substitution shifts the temperature of the maximum of the effect toward lower temperatures while leaving its magnitude practically unchanged. The magnetocaloric effect in the La0.7Ca0.3Mn16O3 + La0.7Ca0.3Mn18O3 sandwich structure has been measured by the direct method. It has been shown that fabrication of a sandwich from materials with close temperatures of the maxima of the magnetocaloric effect permits increasing the relative cooling power (RCP) compared with that of the starting materials.

MOCVD Buffer and Superconducting Layers on Non-Magnetic Biaxially Textured Tape for Coated Conductor Fabrication

In this article, we present recent developments in the metal-organic chemical vapor deposition (MOCVD) route to coated conductor fabrication made at SuperOx. Two new buffer layer architectures on nonmagnetic Ni-Cr-W biaxially textured substrates are described. With the use of these architectures we have achieved critical currents in the range of 100-140 A/cm-width for the fully MOCVD produced coated conductors on Ni-Cr-W in the reel-to-reel mode. We have also demonstrated over 10-m-long MOCVD-high temperature superconductor tapes on the ion beam assisted deposition templates with Ic exceeding 300 A/cm-width.

Specific heat and low-field magnetocaloric effect in A-site ordered PrBaMn2O6 manganite

The specific heat and magnetocaloric effect (MCE) of A-site ordered PrBaMn2O6 manganite have been studied. The anomalies caused by the ferromagnetic (FM) and antiferromagnetic (AFM) phase transitions are revealed in the specific heat curve. Direct and inverse MCE are observed at the Curie and Néel points correspondingly. A value of the inverse MCE in the heating run is smaller than in the cooling regime. We attribute this effect to the competition between FM and AFM interactions. A significant advantage of PrBaMn2O6 as a magnetocaloric material is an MCE spanning a broad range of temperature with a maximum at room temperature.