No abstract

Oxide self-assembly is a promising bottom-up approach for fabricating new composite materials at the nanometer length scale. Tailoring the properties of such systems for a wide range of electronic applications depends on the fundamental understanding of the interfaces between the constituent phases. We show that the nanoscale strain modulation in self-assembled systems made of high-T(c) superconducting films containing nanocolumns of BaZrO(3) strongly affects the oxygen composition of the superconductor. Our findings explain the observed reduction of the superconducting critical temperature.

Ba2RENbO6 (RE = rare earth elements including Y) compounds are considered new additives for superior flux-pinning in YBa2Cu3O7-δ (YBCO) films due to their excellent chemical inertness to and large lattice mismatches with YBCO. Simultaneous laser ablation of a YBCO target and a Nb metal foil attached to the surface of the target resulted in epitaxial growth of YBCO films having columnar defects comprised of self-aligned Ba2YNbO6 (BYNO) nanorods parallel to the c-axis of the film. Compared to pure YBCO, YBCO+BYNO films exhibited no Tc reduction as well as superior Jc performance with higher self- and in-field Jc by a factor of 1.5–7 and also exhibited a strong Jc peak for H∥c indicative of strong c-axis correlated flux-pinning.

Deterministic control of magnetization by light, often referred to as all-optical switching (AOS), is an attractive recording method for magnetic nanotechnologies because magnetization control becomes possible without the need of an external magnetic field 7-11 and therefore incorporates the potential for ultra-fast magnetization switching up to 1000 times faster than that by magnetic fields while using lower energies 12 . The first demonstration of the magnetization switching by light was in ferrimangnetic GdFeCo film which is a magneto-optical material 7 where the Gd and FeCo spin sub-lattices are antiferromagnetically exchange coupled. While several mechanisms for the ultrafast magnetization switching of GdFeCo have been explored [14][15][16] , the current understanding for AOS in GdFeCo is that the ultrafast laser excitation demagnetizes the two sublattices at different Hall cross region to measure the evolution of the magnetization to a series of ultrafast laser pulses.We initially used 40 optical pulses for the first two exposure steps, and then, increased to 80 pulses for the next six exposure steps (see methods and given by (N -N)/(N + N). We assume that with each optical pulse there is a switching probability from the spin-up to spin-down state given by P1 and from spin-down to spin-up by P2. The number of FePt grains with spin-up and spin-down states after the n pulses can be expressed by the following:The fitted lines to Eq. What is the origin for different switching probability of P1 and P2 for circularly polarized light pulses? The fact that linear light leads to demagnetization of the sample suggest that heating of the FePt grains by the femto-second laser exposure is sufficient to cause thermal activated reversal.The circularly polarized light then breaks the symmetry of the system favoring one magnetic state 6 over the other and leading to an imbalance in the P1 and P2. This symmetry breaking could result from a direct interaction between the light and the magnetic systems such as the inverse Faraday field that prefers one direction over the other 22 . The difference in P1 and P2 could also arise from differential absorption for RCP and LCP (i.e. magnetic circular dichroism) that will result in a slight difference in temperature for one set of grains compared to the other. 17 We have roughly estimated the difference in temperature needed during the optical excitation to explain the difference in switching probability using a simple Arrhenius-Néel model for single domain particles (see supplementary section for details). A temperature difference of 1-2 K would be sufficient to explain the difference in P1 and P2 observed in Fig. 1, which is consistent with typical dichroism differences in magnetic metals. 17However, independent of the mechanism we find that magnetic switching for granular FePt films is statistical in nature in contrast to the reports on GdFeCo films. Because of this we don't achieve full deterministic switching, which would be needed for magnetic recording applications. To ac...