Scientists investigated the magnetic properties of overlapping layers of platinum, cobalt and gadolinium
Research conducted on the Sabiá beamline at Sirius by scientists from the Brazilian Center for Research in Energy and Materials (CNPEM) and several universities investigated the behavior of magnetic materials and has resulted in the first scientific publication involving data obtained from this beamline.
The study appeared in Communications Physics, a Nature Portfolio journal, and demonstrated that the interaction between platinum, cobalt and gadolinium atoms in thin layers can result in unexpected magnetic behavior. The Sabiá beamline is open for regular research proposals, expanding the possibilities for scientists from across Brazil to investigate the magnetic and structural properties of materials.
Different types of magnetism
The magnetic properties of a material are directly related to the magnetic spins of its atoms. Scientists describe the intensity and direction of the resulting magnetic field as the magnetic moment. When the magnetic moments of different atoms arrange themselves in an orderly manner, the material may exhibit different types of magnetism.
In ferromagnetic materials like iron and cobalt, the magnetic moments align to point in the same direction, resulting in strong magnetization; this is the most common type of magnetism we find under everyday conditions. And in antiferromagnetism, for example, the magnetic moments of adjacent atoms are parallel but align in opposite directions, resulting in weak magnetism or canceling it out entirely.
Meanwhile, paramagnetic materials are those whose magnetic moments only align in the presence of an external field. Other magnetic phases such as diamagnetism, ferrimagnetism, and a new type known as altermagnetism are investigated in condensed matter physics. The origin of these different magnetic responses lies in the interactions between the spins of the electrons and the electronic structures of the atoms involved.
Magnetic behavior of cobalt, gadolinium and platinum
The three elements involved in the research using the Sabiá beamline exhibited different types of magnetism. Cobalt (Co) is a transition metal known for its strong ferromagnetism. Gadolinium (Gd), an element in the lanthanide series, may display paramagnetic or ferromagnetic behavior depending on the temperature. And platinum (Pt) exhibits paramagnetism; in other words, it is not magnetic in its natural state but may acquire magnetic moments which are induced when it is in contact with a ferromagnetic material like cobalt via the effects of magnetic proximity and exchange.
Technical simulations by the researchers predicted that combining cobalt, platinum and gadolinium in thin layers would induce an inverted magnetic moment in Gd in ambient conditions. This inverted state predicted by the theoretical calculations would be transferred from Co to Gd by the proximity effect, when the magnetic moments within the Gd layer change direction as they move away from the Co/Gd interface. The experiment on the Sabiá beamline was planned to verify this predicted behavior.
Sample holders within the Sabiá experimental station where the XMCD experiments were performed. The samples were mounted on carbon tape attached to a molybdenum plate.
“Sample preparation was essential. We prepared a heterostructure composed of a 1-nm layer of platinum, followed by a 1.5-nm-thick layer of cobalt and another 1-nm layer of gadolinium, and repeated this combination ten times to form a multilayer structure,” said Jeovani Brandão, a researcher at the Sabiá beamline and lead author of the article.
X-ray magnetic circular dichroism (XMCD)
To investigate the magnetic states of atoms in each layer within the heterostructure, the researchers used X-ray magnetic circular dichroism, also known as XMCD. This technique is based on the difference between selective absorption of electromagnetic radiation in the X-ray spectrum with circular polarization to the right and left in relation to the magnetic orientation of the sample. The difference in X-ray absorption reveals details about the orientation and magnitude of the magnetic moments, making it possible to obtain chemically-selective information about the element and differentiate the magnetic behavior of the cobalt, gadolinium and platinum on an individual level.
Superconducting coil in the Sabiá beamline at Sirius that was used to subject the sample to intense magnetic fields of up to 9 T.
To determine this difference, it is essential to analyze the absorption of X-rays in different energy ranges, adjusted according to the elements present in the material. This X-ray scanning is done using the precise control allowed by the delta undulator installed on the Sabiá beamline and a monochromator, which makes it possible to adjust both the radiation polarization and the energy range with extreme accuracy, an essential ability for XMCD experiments on complex systems like the multilayer structures in this research.
The inverted spin state
Under typical conditions, the proximity-induced magnetic moments in gadolinium tend to align opposing those of cobalt. The findings from the research on the Sabiá beamline reveal that when influenced by an external magnetic field and proximity interactions with other layers of the Pt/Co/Gd heterostructure, part of the magnetic moments of the gadolinium far from the Co/Gd interface inverted their direction: in other words, they aligned themselves in the same direction as cobalt, a behavior that had not yet been reported in this type of system, known as a flipped spin state (FSS).
In this new state (which was predicted in theoretical simulations), magnetic moments in different directions coexist within the same layer of gadolinium. This was confirmed experimentally thanks to the XMCD technique offered at the Sabiá beamline at Sirius, which makes it possible to measure magnetism at individual points within a single layer of this element. This discovery challenges the classical models of magnetic coupling, and suggests that electronic states in ultra-thin heterostructures can be manipulated in a more complex manner than previously thought.
“Although this is a study on fundamental physics, we can glimpse potential technological applications for the observed magnetic state. By understanding in more detail how magnetic moments arrange themselves in materials comprised of such thin layers, we can pave the way toward developing more efficient new devices based on magnetic memory, with implications for data storage,” notes Brandão. Learn more about the Sabiá beamline.
About LNLS
The Brazilian Synchrotron Light National Laboratory (LNLS) works with scientific research and technological development that involves synchrotron light, focusing on the operation and utilization of the multidisciplinary potential of Sirius, the country’s most advanced scientific infrastructure. With ten research stations already online and open to the scientific and industrial communities, Sirius allows thousands of researchers from various areas to test their hypotheses about the microscopic mechanisms that produce the properties of both natural and synthetic materials which are used in a variety of fields such as health, the environment, energy, and agriculture. LNLS is part of the Brazilian Center for Research in Energy and Materials (CNPEM) in Campinas, São Paulo, a private, non-profit organization overseen by the Ministry of Science, Technology, and Innovation (MCTI).
About CNPEM
The Brazilian Center for Research in Energy and Materials (CNPEM) is a state-of-the-art, multi-user and multidisciplinary scientific environment with activities on different fronts within the Brazilian National System for Science, Technology and Innovation. A social organization overseen by the Ministry of Science, Technology and Innovation (MCTI), CNPEM is driven by research that impacts the areas of health, energy, renewable materials, and sustainability. CNPEM is responsible for Sirius, the country’s largest scientific research infrastructure, and is currently constructing Project Orion, a laboratory complex for advanced pathogen research. Highly specialized science and engineering teams, sophisticated infrastructure open to the scientific community, strategic lines of investigation, innovative projects involving the productive sector, and training for researchers and students are the pillars of this institution that is unique in Brazil and able to serve as a bridge between knowledge and innovation. The research and development activities at CNPEM are carried out by its National Laboratories in the areas of Synchrotron Light (LNLS), Biosciences (LNBio), Nanotechnology (LNNano), and Biorenewables (LNBR), as well as the Ilum School of Science, which offers a bachelor’s degree program in science and technology with support from the Ministry of Education (MEC).
