Featured Research

from universities, journals, and other organizations

Spintronics: Nano magnets arise at 2-D boundaries

Date:
November 14, 2013
Source:
Rice University
Summary:
According to a new theory, imperfections in certain two-dimensional materials create the conditions by which nanoscale magnetic fields arise.

Rice theorists have discovered magnetic fields (blue) are created at grain boundaries in two-dimensional dichalcogenides. Dislocations along these boundaries, where atoms are thrown out of their regular hexagonal patterns, force electron spins into alignments that favor magnetism.
Credit: Zhuhua Zhang

When you squeeze atoms, you don't get atom juice. You get magnets.

According to a new theory by Rice University scientists, imperfections in certain two-dimensional materials create the conditions by which nanoscale magnetic fields arise.

Calculations by the lab of Rice theoretical physicist Boris Yakobson show these imperfections, called grain boundaries, in two-dimensional semiconducting materials known as dichalcogenides can be magnetic. This may lead to new strategies for the growing field of spintronics, which takes advantage of the intrinsic spin of electrons and their associated magnetic fields for electronic and computing devices.

The discovery by Yakobson, lead author Zhuhua Zhang and their colleagues was reported online this week in the American Chemical Society journal ACS Nano.

Dichalcogenides are hybrids that combine transition metal and chalcogen atoms, which include sulfur, selenium and tellurium. The Yakobson group focused on semiconducting molybdenum disulfide (MDS) that, like atom-thick graphene, can be grown via chemical vapor deposition (CVD), among other methods. In a CVD furnace, atoms arrange themselves around a catalyst seed into familiar hexagonal patterns; however, in the case of MDS, sulfur atoms in the lattice alternately float above and below the layer of molybdenum.

When two growing blooms meet, they're highly unlikely to line up, so the atoms find a way to connect along the border, or grain boundary. Instead of regular hexagons, the atoms are forced to find equilibrium by forming adjoining rings known as dislocations, with either five-plus-seven nodes or four-plus-eight nodes.

In graphene, which is generally considered the strongest material on Earth, these dislocations are weak points. But in MDS or other dichalcogenides, they have unique properties.

"It doesn't matter how you grow them," Yakobson said. "These misoriented areas eventually collide, and that's where you find topological defects. It turns out that -- and I like this mechanistic metaphor -- they squeeze magnetism out of nonmagnetic material."

In previous work, Yakobson found dislocations create atom-width conducting lines and dreidel-shaped polyhedra in MDS. This time, the team dug deeper to find that dislocation cores turn magnetic where they force spinning electrons to align in ways that don't cancel each other out, as they do in a flawless lattice. The strength of the magnets depends on the angle of the boundary and rises with the number of dislocations necessary to keep the material energetically stable.

"Every electron has charge and spin, both of which can carry information," Zhang said. "But in conventional transistors, we only exploit the charge, as in field-effect transistors. For newly emerged spintronic devices, we need to control both charge and spin for enhanced efficiency and enriched functions."

"Our work suggests a new degree of freedom -- a new controlling knob -- for electronics that use MDS," Yakobson said. "The ability to control the magnetic properties of this 2-D material makes it superior to graphene in certain respects."

He said the dislocation rings of four and eight atoms are not energetically favored in graphene and unlikely to occur there. But in the materials that mix two elements, certain grain boundary configurations will very likely create conditions where similar elements, wishing to avoid contact with each other, will instead bond with their chemical opposites.

"The system avoids mono-elemental bonds," Yakobson said. "The chemistry doesn't like it, so four-eight offers a benefit." Those defects are also the strongest sources of magnetism at certain grain boundary angles, he said; at some angles, the boundaries become ferromagnetic.

The team proved its theory through computer models designed to isolate and control the effects of the nanoribbons' edges and grain boundary dipoles that could skew the results. They also determined that grain boundary angles between 13 and 32 degrees force a progressive overlap between the dislocations' spins. With sufficient overlap, the spins become magnetically coupled and broaden into electronic bands that support spin-polarized charge transport along the boundary.

Now, Yakobson said, "The challenge is to find a way to experimentally detect these things. It's quite difficult to resolve it at this spatial resolution, especially when some of the experimental methods, like electron beams, would destroy the material."

Co-authors of the paper are Rice postdoctoral researcher Xiaolong Zou and Vincent Crespi, distinguished professor of physics, materials science and engineering, and chemistry at The Pennsylvania State University. Yakobson is Rice's Karl F. Hasselmann Professor of Mechanical Engineering and Materials Science, a professor of chemistry and a member of the Richard E. Smalley Institute for Nanoscale Science and Technology.

A U.S. Army Research Office Multidiscipline University Research Initiative grant, the National Science Foundation and the Robert Welch Foundation supported the research. Computations were performed on the Data Analysis and Visualization Cyberinfrastructure supercomputer administered by Rice's Ken Kennedy Institute for Information Technology.


Story Source:

The above story is based on materials provided by Rice University. The original article was written by Mike Williams. Note: Materials may be edited for content and length.


Journal Reference:

  1. Zhuhua Zhang, Xiaolong Zou, Vincent H. Crespi, Boris I. Yakobson. Intrinsic Magnetism of Grain Boundaries in Two-Dimensional Metal Dichalcogenides. ACS Nano, 2013; 131111004807002 DOI: 10.1021/nn4052887

Cite This Page:

Rice University. "Spintronics: Nano magnets arise at 2-D boundaries." ScienceDaily. ScienceDaily, 14 November 2013. <www.sciencedaily.com/releases/2013/11/131114142209.htm>.
Rice University. (2013, November 14). Spintronics: Nano magnets arise at 2-D boundaries. ScienceDaily. Retrieved July 28, 2014 from www.sciencedaily.com/releases/2013/11/131114142209.htm
Rice University. "Spintronics: Nano magnets arise at 2-D boundaries." ScienceDaily. www.sciencedaily.com/releases/2013/11/131114142209.htm (accessed July 28, 2014).

Share This




More Matter & Energy News

Monday, July 28, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

The Carbon Trap: US Exports Global Warming

The Carbon Trap: US Exports Global Warming

AP (July 28, 2014) AP Investigation: As the Obama administration weans the country off dirty fuels, energy companies are ramping-up overseas coal exports at a heavy price. (July 28) Video provided by AP
Powered by NewsLook.com
Europe's Highest Train Turns 80 in French Pyrenees

Europe's Highest Train Turns 80 in French Pyrenees

AFP (July 25, 2014) Europe's highest train, the little train of Artouste in the French Pyrenees, celebrates its 80th birthday. Duration: 01:05 Video provided by AFP
Powered by NewsLook.com
TSA Administrator on Politics and Flight Bans

TSA Administrator on Politics and Flight Bans

AP (July 24, 2014) TSA administrator, John Pistole's took part in the Aspen Security Forum 2014, where he answered questions on lifting of the ban on flights into Israel's Tel Aviv airport and whether politics played a role in lifting the ban. (July 24) Video provided by AP
Powered by NewsLook.com
Creative Makeovers for Ugly Cellphone Towers

Creative Makeovers for Ugly Cellphone Towers

AP (July 24, 2014) Mobile phone companies and communities across the country are going to new lengths to disguise those unsightly cellphone towers. From a church bell tower to a flagpole, even a pencil, some towers are trying to make a point. (July 24) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins