Spontaneous formation of hierarchical wrinkles in Cr films deposited on silicone oil drops with constrained edges.

We report on the spontaneous formation of hierarchical wrinkling patterns in Cr films deposited on silicone oil drops with constrained edges. The appearance of the wrinkling patterns is strongly dependent on the film thickness and the size of the silicone oil drop. Because the Cr film at the drop edge is constrained due to the strong adhesion between the film and the glass surface, the wrinkle wavelength merely depends on the distance starting from the drop edge. When the distance increases, the wavelength increases quickly first, and then it slows down gradually in compliance with a simple power law. The evolution of the wrinkle amplitude is similar to that of the wavelength, but it is also closely related to the film thickness and the oil drop size. Based on the fact that the silicone oil is polymerized to form an elastic layer during deposition, the formation and evolution of the hierarchical wrinkling patterns have been analyzed in detail.

Strain driven enhancement of ferroelectricity and magnetoelectric effect in multiferroic tunnel junction.

The strain effect on the ferroelectric and magnetoelectric coupling in multiferroic tunnel junction (MFTJ) Co/BaTiO3/Co has been investigated systematically by using first-principles calculations within density functional theory. It is found that both in-plane compressive strain and uniaxial tensile strain lead to the enhancement of ferroelectric polarization stability and intensity of magnetoelectric coupling in the MFTJ. There is a transition from the paraelectric phase to the ferroelectric phase for the BaTiO3 layer in MFTJ when the loaded in-plane compressive strain increases up to -2.8% and the corresponding average ferroelectric polarization is about 0.13 C m(-2). Meanwhile, the calculated surface magnetoelectric coefficients increase with increasing in-plane compressive strain. Similar phenomena have been also observed in the case of uniaxial tensile strain implemented in MFTJ. The results suggest that the ferroelectric polarization and magnetoelectric coupling in multiferroic tunnel junctions can be controlled by strain and we expect that this study can provide a theoretical basis for the design of spintronic devices.