Examining the Temperature Dependence of Louche Formation in Absinthe.

Absinthe is an anise-flavored alcohol that is typically served by adding cold water to form a cloudy green louche, similar to the cloudy white louche of ouzo. This microemulsion formation, due to the competing interactions within the oil-alcohol-water system, has been termed the ouzo effect. Previous work has examined the ternary oil-alcohol-water phase diagram in ouzo and limoncello. Additional work has also characterized the droplet size and stability of microemulsions in ouzo, limoncello, and pastis. However, less work has been done to examine the effect of temperature on louche formation despite the fact that the louche is traditionally formed by adding ice cold water. This work demonstrates that both the maximum turbidity and the fraction of alcohol at maximum turbidity are temperature-dependent. The louche formation can be fit with a logistic curve, and the resulting fit parameters are linear with temperature. Optical images show that the increased turbidity correlates with an increase in the number of droplets in the microemulsion.

Reversing the circulation of ferromagnetic nanodisks with a local circular magnetic field.

Ferromagnetic nanodisks have a unique closed-flux vortex state with two degrees of freedom that results in four different magnetization states that are degenerate in energy and stable against thermal fluctuations. Such disks could be interesting for magnetic memory devices if the independent switching of each degree of freedom can be realized. Polarity switching of the vortex core has been demonstrated, but it is difficult to manipulate switching of the vortex due to the high symmetry of the structure. In this work, we reverse the circulation direction of a circular ferromagnetic nanodisk by applying a local circular Oersted field via a metallic atomic force microscope tip placed at the center of the disk. The resulting field reverses the circulation of the vortex without switching the orientation of the core. Switching of the vortex is accomplished by the sudden increase in the current that occurs when there is dielectric breakdown of a thin insulating layer on top of the disk. Micromagnetic simulations indicate that a line current concentrated in the center of a nanodisk can reverse the magnetization of the disk at a value over one order of magnitude smaller than the current required if the current is instead uniformly distributed across the cross section of disk. These results can be applied to reducing the switching current in circularly symmetric device structures.

Writing and deleting single magnetic skyrmions.

Topologically nontrivial spin textures have recently been investigated for spintronic applications. Here, we report on an ultrathin magnetic film in which individual skyrmions can be written and deleted in a controlled fashion with local spin-polarized currents from a scanning tunneling microscope. An external magnetic field is used to tune the energy landscape, and the temperature is adjusted to prevent thermally activated switching between topologically distinct states. Switching rate and direction can then be controlled by the parameters used for current injection. The creation and annihilation of individual magnetic skyrmions demonstrates the potential for topological charge in future information-storage concepts.

Information transfer by vector spin chirality in finite magnetic chains.

Vector spin chirality is one of the fundamental characteristics of complex magnets. For a one-dimensional spin-spiral state it can be interpreted as the handedness, or rotational sense of the spiral. Here, using spin-polarized scanning tunneling microscopy, we demonstrate the occurrence of an atomic-scale spin spiral in finite individual bi-atomic Fe chains on the (5×1)-Ir(001) surface. We show that the broken inversion symmetry at the surface promotes one direction of the vector spin chirality, leading to a unique rotational sense of the spiral in all chains. Correspondingly, changes in the spin direction of one chain end can be probed tens of nanometers away, suggesting a new way of transmitting information about the state of magnetic objects on the nanoscale.