Magnetic nanostructures by adaptive twinning in strained epitaxial films

We exploit the intrinsic structural instability of the Fe70Pd30 magnetic shape memory alloy to obtain functional epitaxial films exhibiting a self-organized nanostructure. We demonstrate that coherent epitaxial straining by 54% is possible. The combination of thin film experiments and large-scale first-principles calculations enables us to establish a lattice relaxation mechanism, which is not expected for stable materials. We identify a low twin boundary energy compared to a high elastic energy as key prerequisite for the adaptive nanotwinning. Our approach is versatile as it allows to control both, nanostructure and intrinsic properties for ferromagnetic, ferroelastic and ferroelectric materials.Comment: Final version. Supplementary information available on request or at the publisher's websit

Microstructure Formation and Resistivity Change in CuCr during Rapid Solidification

The formation of the surface-near microstructure after a current interruption of CuCr contact materials in a vacuum interrupter is characterized by a fast heating and subsequently rapid solidification process. In the present article, we reveal and analyse the formation of two distinct microstructural regions that result from the heat, which is generated and dissipated during interruption. In the topmost region, local and global texture, as well as the resulting microstructure, indicate that both Cu and Cr were melted during rapid heating and solidification whereas in the region underneath, only Cu was melted and elongated Cu-grains solidified with the <001>-direction perpendicularly aligned to the surface. By analysing the lattice parameter of the Cu solid solution, a supersaturation of the solid solution with about 2.25 at % Cr was found independent if Cu was melted solely or together with the Cr. The according reduction of electrical conductivity in the topmost region subsequent to current interruption and the resulting heat distribution are discussed based on these experimental results

Microstructure Formation and Resistivity Change in CuCr during Rapid Solidification

The formation of the surface-near microstructure after a current interruption of CuCr contact materials in a vacuum interrupter is characterized by a fast heating and subsequently rapid solidification process. In the present article, we reveal and analyse the formation of two distinct microstructural regions that result from the heat, which is generated and dissipated during interruption. In the topmost region, local and global texture, as well as the resulting microstructure, indicate that both Cu and Cr were melted during rapid heating and solidification whereas in the region underneath, only Cu was melted and elongated Cu-grains solidified with the -direction perpendicularly aligned to the surface. By analysing the lattice parameter of the Cu solid solution, a supersaturation of the solid solution with about 2.25 at % Cr was found independent if Cu was melted solely or together with the Cr. The according reduction of electrical conductivity in the topmost region subsequent to current interruption and the resulting heat distribution are discussed based on these experimental results

Chemical solution deposition of Y₁₋ₓGdₓBa₂Cu₃O7−δ_{7-δ} –BaHfO₃ nanocomposite films: combined influence of nanoparticles and rare-earth mixing on growth conditions and transport properties

Y1−xGdxBa2Cu3O7−δ–BaHfO3 (YGBCO–BHO) nanocomposite films containing 12 mol% BHO nanoparticles and different amounts of Gd were prepared by chemical solution deposition following the trifluoroacetic route on SrTiO3 single crystals in order to study the influence of the rare earth stoichiometry on structure, morphology and superconducting properties of these films. We optimized the growth process for each of several Gd contents of the 220 nm thick YGBCO–BHO films by varying crystallization temperature and oxygen partial pressure. This optimization process led to the conclusion that mixing the rare earths in YGBCO–BHO films leads to wider growth parameter windows compared to YBCO-BHO and GdBCO-BHO films giving larger freedom for selecting the most convenient processing parameters in order to adapt to different substrates or applications which is very important for the industrial production of coated conductors. The optimized films show a continuous increase of Tc with Gd content x from ∼90 K for the YBCO-BHO films to ∼94 K for the GdBCO-BHO films. Consequently, an increase of the 77 K self-field Jc with Gd content is observed reaching values > 7 MA cm−2 for Gd contents x > 0.5. The transport properties of these films under applied magnetic fields are significantly improved with respect to the pristine YBCO films. All YGBCO–BHO nanocomposite films grew epitaxially with c-axis orientation and excellent out-of-plane and in-plane texture. The films are dense with a low amount of pores and only superficial indentation