Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Neutrons tap into magnetism in topological insulators at high temperatures

10.05.2016

A multi-institutional team of researchers has discovered novel magnetic behavior on the surface of a specialized material that holds promise for smaller, more efficient devices and other advanced technology.


This is an illustration showing structure of Bi2Se3-EuS bilayer film. On the top layer the depth profile of the magnetization vector distribution of Eu atoms is represented by green arrows. The light purple spheres represent Bi2Se3 interfacial layers magnetized in close proximity to EuS FMI.

Credit: ORNL/Jill Hemman

Researchers at the Department of Energy's Oak Ridge National Laboratory, Massachusetts Institute of Technology and their collaborators used neutron scattering to reveal magnetic moments in hybrid topological insulator (TI) materials at room temperature, hundreds of degrees Fahrenheit warmer than the extreme sub-zero cold where the properties are expected to occur.

The discovery promises new opportunities for next-generation electronic and spintronic devices such as improved transistors and quantum computing technologies. Their research is discussed in a paper published in the journal Nature.

TIs are relatively new materials, said Valeria Lauter, coauthor and instrument scientist at the Spallation Neutron Source, a DOE Office of Science User Facility at ORNL. A unique property of TIs is that electrons can flow on the surface without dissipation, while the bulk of the material serves as an electrical insulator--ideal for semiconducting materials.

"The properties of TIs are fantastic," Lauter said, "but in order to use them in devices we need to be able to introduce magnetism on the surface without disturbing the bulk insulating properties of the material."

This can be achieved in two ways: by impurity doping, where magnetic atoms are incorporated onto the TI surface, or by proximity coupling, where magnetism is induced by interfacing the TI with a layer of ferromagnetic insulating film.

The first method presents a problem, however. Doping can cause magnetic clusters if the atoms are not uniformly distributed, resulting in decreased electron transport controllability. Proximity coupling, on the other hand, can be obtained on clean, atomically sharp interfaces with crystalline orientations between two materials.

Using the proximity coupling method, Lauter's collaborators at the Massachusetts Institute of Technology engineered hybrid bilayer heterostructures of bismuth selenide (Bi2Se3) TIs combined with a europium sulfide (EuS) ferromagnetic insulator (FMI). The definite spin directions of the FMI in proximity to the TI enable dissipation-free, spin-polarized (i.e. magnetic) electron flow in a thin layer close to the interface. That marriage forms a mutually magnetic relationship, Lauter said, though it's difficult to establish.

"The first challenge is to grow the system," she said. "The second is to measure its magnetism-- not an easy thing to do when the small magnetic signals are hidden between two materials."

The bulk EuS itself presents a particular challenge in that it's limited by a low Curie temperature (Tc), the temperature at which a material ceases to demonstrate ferromagnetic behavior--in this case a temperature of approximately 17 kelvins (17 K), or negative 430 degrees Fahrenheit, well below a suitable room temperature for electronic devices.

To identify the hidden magnetic signals, Lauter used a polarized neutron reflectometry (PNR) technique at the Magnetism Reflectometer instrument on SNS beam line 4A. Neutrons are well-suited for this type of detection because of their sensitivity to magnetism and their innate ability to pass through materials in a nondestructive fashion, elucidating structural and magnetic depth profiles. Likewise, PNR is suited to studying Bi2Se3-EuS interfaces because it is the only technique that can measure the absolute value of magnetic moments in the materials.

The first sample measurements were taken at 5 K, well below the EuS Tc of 16.6 K. From there, Lauter took measurements above the Tc, starting at 25 K, and to her surprise, the system was still highly magnetic.

"This was quite unexpected. Above this temperature [16.6 K] nothing in the system should be magnetic," Lauter said. "So I measured at 35 K, then 50 K, and it was still magnetic. I measured all the way up to room temperature [300 K, 80 F] at several points and saw that a small magnetization was still present."

Lauter notes at room temperature the level of magnetism is reduced by more than a factor of 10 compared to its 5 K value. Nevertheless, she says, it remains substantial considering no magnetism is found in EuS layers above 50 K without the TI interface.

To substantiate the results, subsequent measurements were taken using different samples with varying thickness combinations. Throughout the experiments, neutrons revealed that ferromagnetism extends approximately 2 nanometers into the Bi2Se3 from the interface.

"This discovery could open new doors for designing spintronic devices," Lauter said. "Ferromagnetic surface states in TIs are also thought to enable the emergence of exotic phenomena such as Majorana fermions--potential building blocks for quantum computers.

"These are just the properties we know of today, and we're continuing to find even more."

###

Co-authors of the paper, titled "A high-temperature ferromagnetic topological insulating phase by proximity coupling," include lead author Ferhat Katmis, Flavio S. Nogueira, Badih A. Assaf, Michelle E. Jamer, Peng Wei, Biswarup Satpati, John W. Freeland, Ilya Eremin, Don Heiman, Pablo Jarillo-Herrero, and Jagadeesh S. Moodera.

Additional contributions and complementary measurements were obtained from DOE's Argonne National Laboratory, Northeastern University, The Leibniz Institute for Solid State and Materials Research in Dresden, Ruhr University Bochum, the Saha Institute of Nuclear Physics in India, and the Department of Physics Ecole Normale Superieure in Paris.

The research conducted at ORNL's Spallation Neutron Source was supported DOE's Office of Science. The paper is available at http://www.nature.com/nature/journal/vaop/ncurrent/full/nature17635.html.

UT-Battelle manages ORNL for the DOE's Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov/.

Media Contact

Jeremy Rumsey
rumseyjp@ornl.gov
865-576-2038

 @ORNL

http://www.ornl.gov 

Jeremy Rumsey | EurekAlert!

More articles from Physics and Astronomy:

nachricht From rocks in Colorado, evidence of a 'chaotic solar system'
23.02.2017 | University of Wisconsin-Madison

nachricht Prediction: More gas-giants will be found orbiting Sun-like stars
22.02.2017 | Carnegie Institution for Science

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

NASA eyes Pineapple Express soaking California

24.02.2017 | Earth Sciences

New gene for atrazine resistance identified in waterhemp

24.02.2017 | Agricultural and Forestry Science

New Mechanisms of Gene Inactivation may prevent Aging and Cancer

24.02.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>