Brazilian group gains international acclaim with research on magnetic semiconductors

Scientists develop an innovative methodology that is promising for computer processors and memory in the future

By Fábio de Castro

Agência FAPESP – A group of scientists from the Technological Institute of Aeronautics (ITA) have gained international acclaim for their advances in materials sciences on magnetic semiconductors, which can integrate the processors and memories of computers in the future.

Professor Ronaldo Rodrigues Pelá, of ITA’s Physics Department, received the Young Scientist Best Paper Award at the International Conference on the Physics of Semiconductors held at the Eidgenössische Technische Hochschule (ETH) in Zurich, Switzerland.

The award was given to a total of 15 participants who had defended doctoral theses within the last year and who had presented high-impact studies as first author in the semiconductor field. A committee formed by researchers from around the globe selected the works. The conference brought together more than 800 participants from the field.

Developed as part of his doctorate at ITA, the study presented by Pelá and published in the May edition of Applied Physics Letters discusses an innovative method for precise and efficient simulation of magnetic semiconductor materials.

In addition to Pelá, two other ITA professors participated in the article—Lara Kühl Teles from the Fundamental Sciences Division of the Physics Department and Marcelo Marques from the Electronic Engineering Division—along with Jurgen Furthmüller from Friedrich-Schiller University of Jena in Germany.

Pelá, Teles and Marques are part of ITA’s Semiconductor Materials and Nanotechnology Group (GMSN), which was formed from a theoretical study project on semiconductor alloys with applications in spintronics and optoelectronics, coordinated by Teles and funded by FAPESP from 2007-2012 under its Young Investigators grant program.

Pelá’s trip to the conference in Zurich was also funded by FAPESP under its Regular Foreign Meeting Assistance grants. The researcher also received FAPESP funding for Scientific Initiation and a direct doctorate at ITA, under the direction of Teles. Furthmüller came to Brazil in 2011 as a visiting researcher to ITA, also with FAPESP funding under the Foreign Visitor Assistance grant program.

According to Teles, GMSN develops first principles calculations for semiconductor materials, semiconductor alloys, quantum wells, quantum points, quantum strings, nanostrings, interfaces, impurities, graphene and magnetic semiconductors.

“FAPESP’s Young Research project has been very successful in terms of its main objective, which was to create a research group on these themes. The idea was to have a strong group, offering opportunities for young researchers to begin new research lines in emerging centers when they do not exist at the respective institution,” said Teles in an interview with Agência FAPESP.
 
GMSN, according to Teles, currently has three professors, a post-doctoral student, four doctoral students, a master’s student and three in scientific initiation. The group’s scientific production was already a highlight in 2007, when Pelá received an award during the 1st International Conference on Spintronics Materials and Technology, with a study developed in his scientific initiation project.

Focused on semiconductors and nanotechnology, the group, according to Teles, is still actively researching compound and simple semiconductor materials, along with alloys formed based on these materials.

“We conduct theoretical simulations of these materials to obtain certain electronic, structural, thermodynamic and even magnetic properties because there is already a class of magnetic semiconductors,” says Teles.

In addition to conducting simulations of materials, attempting to predict their properties and explaining experimental observations, one line of the group’s research focuses on developing methodologies to obtain special properties, such as those related to excited states, for example. “This is a very important line of research that was only recently included,” affirms Teles.

In 2008, the group published articles in Physical Review on the development of a new methodology to obtain the so-called semiconductor gaps, which are considered one of the main properties of these materials.

The study was developed in partnership with Luiz Guimarães Ferreira, of Universidade de São Paulo’s Physics Institute. In general, according to Teles, the methodologies for obtaining gaps are costly because doing so requires cluster calculations in extremely sophisticated computers or involves many empirical parameters.

“Using a methodology that has low computational and operational costs, without empirical parameters, we managed to obtain a gap that is compatible with an experimental value. This is a major advance, and we hope that within a few years, we will receive broad recognition for this work,” said Teles.

The development of this methodology, according to Teles, was one of the most important research lines developed by GMSN in recent years. The prize-winning award, according to her, is an application of the same methodology for magnetic semiconductor materials.

Another of the GMSN’s important research lines, in Teles’ opinion, is one that studies the physical properties of the interface of semiconductors, heterostructures of semiconductors and nanocompounds (such as graphene) and quantum strings and points. “This is a line connected to nanotechnology, that is, low-dimension materials.”

The group also has a third line of research involving spintronics—a multidisciplinary field whose main theme consists of manipulation of the degrees of freedom of the spin, which is a purely quantum property related to the angular intrinsic movement of electrons. “Magnetic semiconductor materials are part of the spintronics line. In this line, we conduct simulations on devices and study the properties of these materials,” she explains.

The group has had several other publications since 2008, according to Teles. Among the most important, in addition to the award-winning works of Pelá, is the study published by the group in Applied Physics Letters in 2011, describing the application of the methodology for studies related to alloys.

The group also published a series of articles on the simulation of spintronics devices in the Journals of Superconductivity and Novel Magnetism. Several other articles were published in journals such as Physical Review B and Journal of Applied Physics.

The article “Accurate calculation of the Mn-d level in GaMnAs,” by Ronaldo Pelá, Marcelo Marques, Jurgen Furthmüller and Lara Kühl Teles, can be read by subscribers of Applied Physics Letters at http://apl.aip.org.