RE-Nickelborocarbides
The project is focused on the synthesis and characterization of Rare Earth Nickel Borocarbide thin films for the analysis of their superconductive properties. The films are deposited using pulsed laser deposition under UHV atmosphere. High rates up to 1 nm/s are necessary to exhibit a well-oriented in-plane texture. From their superconductive properties, mainly the critical fields and critical currents are investigated. The films are also analyzed for their critical state behaviour within external cooperations.
From the superconductive point of view, Rare Earth Nickel Borocarbides are still interesting because of their complicated and, to some extent, unique interplay of superconductivity and metamagnetic phases in some members of that family. Not only that they exhibit the same physical structure, but the fact that many phenomena can be studied in dependence of chemistry, has moved them into the focus of high research activities.
As one of the projects of the SFB 463 that is related to sample preparation, A4 concentrates on the synthesis and the structural analyses of thin films made from stoichiometric RNBC targets, epitaxially grown on ceramic single crystal substrates. Besides the stoichiometric borocarbides, the focus also lies on disorder (in the superconductive sense). A central question, and mainly the driving force, is the investigation of superconductive electrical transport. Although grain boundaries do not play a big role due to the large coherence length, nevertheless the purity, the atomic order within the Ni-B-planes, the epitaxy, the anisotropy and the magnetic properties have a strong impact on the superconductive currents -- and vice versa they influence the named characteristics of the samples.
Within the project, textured epitaxial [1,2] thin films of YNi2B2C and HoNi2B2C were investigated in terms of their angular dependence of the upper critical field [3,4] and critical currents [5]. Flux jumps were found to appear below 0.7 Tc within homogeneous epitaxial YNi2B2C thin films [6]. Moreover, the superconducting gap was investigated with point contact spectroscopy [7].
Selected pictures (mouse hover displays description):
Selected publications:
1) Haese, K., Hough, D., Holzapfel, B., Schultz, L., In-situ preparation of RENi2B2C (RE - Y, Ho) thin films by pulsed laser deposition, Physica B 294-288: 1105-1106 (2000)
2) Wimbush, S.C., Haese, K., Schultz, L., Holzapfel, B.,
Epitaxial a-axis and c-axis oriented growth of YNi2B2C thin films, Journal of Physics: Condensed Matter 13: 355-360 (2001)
3) Haese, K., Holzapfel, B., Schultz, L.:
The angle dependence of the upper critical field of HoNi2B2C thin films, Physica C 341-348: 761-762 (2000)
4) Wimbush, S.C., Schultz, L., Holzapfel, B.:
Angular Anisotropy of the Upper Critical Field in YNi2B2C
Physica C 408: 83-84 (2004)
5) Wimbush, S.C., Schultz, L., Holzapfel, B.:
Critical Current in YNi2B2C and HoNi2B2C thin films, Physica C 388: 191-192 (2003)
6) Wimbush, S.C., Holzapfel, B., Jooss, C.:
Observation of dendritic flux instabilities in YNi2B2C thin films, Journal of Applied Physics 96 (6): 3589-3591 (2004)
7) Bashlakov, D.L., Naidyuk, Yu.G., Yanson, I.K.
Wimbush, S.C., Holzapfel, B., Fuchs, G., Drechsler, S.-L.:
Distribution of the superconducting gap in an YNi2B2C film studied by point contact spectroscopy, SuST 18 (8): 1094-1099 (2005)