Manufacturing Bits: Aug. 14
Researchers Seek Magnetic Vortex Memories
The motion of a fluid swirling around a center is referred to as a vortex. One example of a vortex is a tornado. Another example is a magnetic vortex state.
Ferromagnetic nanodisks of magnetic vortices, or hurricanes of magnetism of only a few atoms, could one day enable a new class of memory devices. U.S. Department of Energy’s Lawrence Berkeley National Laboratory has discovered that the formation of magnetic vortices in ferromagnetic nanodisks is an asymmetric phenomenon. Kyoto University, the University of Electro-Communications at Chofu, and Japan’s National Institute for Materials Science also participated in the work. http://newscenter.lbl.gov/feature-stories/2012/08/07/new-phenomenon-in-nanodisk-magnetic-vortices/
This is contrary to popular belief, as many assume that the formation of magnetic vortex states should be symmetric. This is because the magnetic vortex has four degenerate states, according to researchers.
Magnetic vortex states are generated in ferromagnetic nanodisks, according to researchers. In the first part of this phenomenon, the spin of electrons causes magnetic moments, they said. This results in a curling of the in-plane magnetization flux lines. The center of these curling flux lines is a needlelike core, or an “eye-of-the-hurricane.” That points either up or down in the plane of the nanodisk, according to researchers.
MTXM images of in-plane (a) and out-of-plane (b) magnetic components in an array of permalloy nanodisks. In-plane magnetic rotation is shown by white arrow (a). Core polarization is marked by black (up) and white (down) spots. Image (c) shows the complete vortex configuration of each nanodisk in the array. (Images courtesy of Im and Fischer)
In the lab, researchers devised nanodisks from a nickel and iron alloy. Using an electron-beam, they patterned large arrays of disks, each with a radius of 500nm and a thickness of 100nm. The arrays were deposited on silicon-nitride membranes.
Using high-resolution full-field magnetic transmission soft X-ray microscopy, researchers conducted micromagnetic simulations. They confirmed an interaction from spin-orbit coupling due to the lack of inversion symmetry near the disk surface.
New Memory Devices Based On Multiferroic Materials
Researchers have discovered that magnetic and dielectric properties can be controlled by substituting other atoms.
The research was conducted by the National Institute for Materials Science in Japan. It collaborated with the Rutherford Appleton Laboratory and the University of Oxford, both in the U.K.
Magnetic dielectrics called multiferroics have recently attracted attention. Multiferroics, which could enable a new type of memory device, include materials that exhibit any type of long range magnetic ordering.
Multiferroic materials that function at room temperature are rare. With these materials, dielectric polarization is controlled by a magnetic field and magnetization is controlled by an electric field. This differs from conventional technology, in which magnetization is controlled by a magnetic field and dielectric polarization is controlled by an electric field.
Using ultra-high pressure synthesis, researchers devised a silver ferrite (AgFeO2) specimen in which silver (Ag) ions are completely substituted for the nonmagnetic copper (Cu) ions in the delafossite oxide (CuFeO2). This could pave the way for the development of next-generation memories and energy conversion materials.
—Mark LaPedus
Tags: ferromagnetic nano disks, Kyoto University, Lawrence Berkeley National Laboratory, magnetic vortex memory, multiferroic material, National Institute of Materials Science, Rutherford Appleton Laboratory, silver ferrite, University of ElectroCommunications, University of Oxford