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Posted: Jan 10, 2017
Magnetic discovery could be tip of the 'ice'berg
(Nanowerk News) A new material, called "rewritable magnetic charge ice," has an unprecedented degree of control over local magnetic fields. The artificial, magnetically charged structure is formed by manipulating local magnetic charges that set the state of the magnetic “bits.”
This new magnetic charge-ice structure demonstrates write-read-erase capabilities at room temperature, which may have implications for new computing technologies (Science, "Rewritable artificial magnetic charge ice").
Nanomagnetic attraction. In a magnetic charge ice with nanoscale magnets arranged in a two-dimensional lattice, each nanomagnet produces a pair of magnetic charges, one positive (red ball on the north pole) and one negative (blue ball on the south pole). The magnetic flux lines (white) point from positive charges to negative charges. Research allowed construction of arrays of reconfigurable nanomagnets (insert). Manipulating the nanomagnets produces three distinct types of states that are reconfigurable (insert). (Image: Yong-Lei Wang, Zhi-Li Xiao, and Wai-Kwong Kwok, Argonne National Laboratory, University of Notre Dame, and Northern Illinois University)
Scientists consider artificial spin ices to be scientific playgrounds, where the mysteries of magnetism might be explored and revealed. By using a new design method, the team tailored the artificial ice states in such a way that may enable their application for room temperature, rewritable data storage, memory, and logic devices, or in magnonics to study spin waves in nanostructures. Rather than focusing on spins, tackling the magnetic charges allows more controllability.
Current magnetic storage and recording devices, such as computer hard disks, contain nanomagnets with two polarities, each of which is used to represent either 0 or 1 — the binary digits, or bits, used in computers.
Over the past decade, scientists have been keenly interested in creating, investigating, and attempting to manipulate the unusual properties of "artificial spin ices." The materials are so named because the spins have a lattice structure that follows the proton positioning ordering found in water ice.
A magnetic charge ice system could have eight possible configurations instead of two, resulting in denser storage capabilities or added functionality unavailable in current technologies.
However, in the past, researchers have been frustrated in their attempts to achieve global and local control of spin-ice magnetic charges.
To overcome this challenge, a research team from Argonne National Laboratory, including the Center for Nanoscale Materials (CNM), University of Notre Dame, and Northern Illinois University decoupled the lattice structure of magnetic spins and the magnetic charges. Decoupling the structure and the charges allowed them to precisely and conveniently tune the magnetic charge ice to any of eight possible charge configurations.
The configurations are two in a Type I ground state, two in a Type II (two-fold symmetric) excited state, and four in a Type III (four-fold symmetric) excited state.
The team used electron beam lithography at CNM to pattern the samples, and a magnetic force microscope equipped with a two-dimensional vector magnet (capable of fine tuning the applied field strength and direction) to demonstrate the array’s local write-read-erase multi-functionality at room temperature.