**Author details**

Andrei L. Solovjov

*B. I. Verkin Institute for Low Temperature Physics and Engineering of National Academy of Science of Ukraine, Lenin ave. 47, Kharkov 61103, Ukraine*

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© 2012 Tournier et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2012 Tournier et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Magnetic Texturing of High-Tc Superconductors** 

Laureline Porcar, Patricia de Rango, Daniel Bourgault and Robert Tournier

The magnetic field is an efficient tool for characterizing materials but also for elaborating them with a determined magnetic and crystallographic microstructure. The main effect of a magnetic field is to align crystallites embedded in the liquid along their easy magnetization axis [1,2]. The texturing is successful when the force exerted on the crystal gives rise to a rotation thanks to the presence of a liquid around the particle. The possibility to texture under a magnetic field is nowadays known and is still studied worldwide. However, in this paper, we aim to focus the attention on the role of the overheating above the liquidus temperature where our experiments and calculations show that nuclei are surviving above this temperature [3-7]. This assumption contradicts the classical nucleation model where intrinsic nuclei are not present above the melting temperature Tm and cannot act as growth nuclei while cooling down the temperature below Tm [8-10]. Furthermore, melts can usually be supercooled below their melting or liquidus temperatures (*T*m). The degree of supercooling (Δ*T*-), measured by the difference between the onset temperature of solidification and *T*m, is affected by various factors, including the level of overheating and the time. The relations between the overheating (Δ*T*+), and the supercooling (Δ*T*-) were studied in Sn and Sn-Pb [11].The dependence of (Δ*T+*) on (Δ*T*-) is a function of the holding time. It is well known that the cooling rate plays an important role in establishing the degree of supercooling since the nucleation of solid structures and thus solidification requires a certain period of time. Reversibly, melting also takes a certain period of time to destroy the order structures. Furthermore, it is worth noting that as long as some residual solid particles (nuclei) exist above the melting temperature, the energy barrier for the nucleation of crystallization during cooling can be reduced and thus the level of supercooling will be nil. As soon as the solid structures in the melt are completely destroyed, a substantial surface energy barrier exists for the nucleation of solid particles upon cooling. Consequently, each supercooling temperature can be associated with a nucleation time. In congruent material, such as Bi, only few crystals are obtained after an overheating of 80°C [1,7]. Then, the magnetic field can act on these remaining nuclei embedded in the liquid

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/48698

**1. Introduction** 

above the melting point.
