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Magnetization Reversal in Cobalt Nanocolumn Structures Obtained by Glancing Angle Deposition

100%

Buchta K., Schmidt C., Trykowski G., Biniak S., Kempiński M., Luciński T.

Acta Physica Polonica A

2012

vol. 121

issue 5-6

1222-1224

An advanced deposition technique known as glancing angle deposition was used to fabricate randomly seeded magnetic cobalt columnar nanostructures. The existence of nanocolumns was confirmed by the cross-section scanning electron microscopy. The evolution in the magnetization reversal mechanism as a function of the film thickness was investigated. The coercivity H_{C} and M_{R}/M_{S} ratio (where M_{R} and M_{S} denote the remanent and saturation magnetization, respectively), derived from the magnetic hysteresis loops, are discussed as a function of the angle between the external magnetic field and the surface normal. The direction of the magnetization easy/hard axis and the columns inclination angle were determined on the basis of the angular dependences of the H_{C} and the M_{R}/M_{S}. A crossover from the coherent rotation, based on the Stoner-Wohlfarth model, to the curling reversal mode was observed.

Nanostructural Superconducting Materials for Fault Current Limiters and Cryogenic Electrical Machines

44%

Prikhna T., Gawalek W., Savchuk Y., Sergienko N., Moshchil V., Sokolovsky V., Vajda J., Tkach V., Karau F., Weber H., Eisterer M., Joulain A., Rabier J., Chaud X., Wendt M., Dellith J., Danilenko N., Habisreuther T., Dub S., Meerovich V., Litzkendorf D., Nagorny P., Kovalev L., Schmidt C., Melnikov V., Shapovalov A., Kozyrev A., Sverdun V., Kosa J., Vlasenko A.

Acta Physica Polonica A

2010

vol. 117

issue 1

7-14

Materials of the Y-Ba-Cu-O (melt-textured YBa_{2}Cu_{3}O_{7-δ}-based materials or MT-YBCO) and Mg-B-O (MgB_{2}-based materials) systems with high superconducting performance, which can be attained due to the formation of regularly distributed nanostructural defects and inhomogeneities in their structure can be effectively used in cryogenic technique, in particular in fault current limiters and electrical machines (electromotors, generators, pumps for liquid gases, etc.). The developed processes of high-temperature (900-800°C) oxygenation under elevated pressure (16 MPa) of MT-YBCO and high-pressure (2 GPa) synthesis of MgB_{2}-based materials allowed us to attain high superconductive (critical current densities, upper critical fields, fields of irreversibility, trapped magnetic fields) and mechanical (hardness, fracture toughness, Young modulus) characteristics. It has been shown that the effect of materials properties improvement in the case of MT-YBCO was attained due to the formation of high twin density (20-22 μm^{-1}), prevention of macrocracking and reduction (by a factor of 4.5) of microcrack density, and in the case of MgB_{2}-based materials due to the formation of oxygen-enriched as compared to the matrix phase fine-dispersed Mg-B-O inhomogeneities as well as inclusions of higher borides with near-MgB_{12} stoichiometry in the Mg-B-O matrix (with 15-37 nm average grain sizes). The possibility is shown to obtain the rather high T_{c} (37 K) and critical current densities in materials with MgB_{12} matrix (with 95% of shielding fraction as calculated from the resistant curve).

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Magnetization Reversal in Cobalt Nanocolumn Structures Obtained by Glancing Angle Deposition

Nanostructural Superconducting Materials for Fault Current Limiters and Cryogenic Electrical Machines