University Scientists Lead the Discovery of Ferromagnetism in Ruthenium
A collaborative effort led by researchers at the University of Minnesota has resulted in the experimental discovery of ferromagnetic properties in Ruthenium, making it the fourth single element with such properties in the periodic table. The discovery opens an exciting new chapter in the fundamental studies of this element, and its application potential in the creation and scaling of magnetic memories, and breaking new ground in computing performance.
The importance and use of ferromagnetism reaches far back into ancient times, when lodestone was used for navigation. Since then only three elements on the periodic table have been found to be ferromagnetic at room temperature–iron (Fe), cobalt (Co), and nickel (Ni). Rare earth element gadolinium (Gd) misses this status by a mere 8 degrees celsius. These magnetic materials have been used for fundamental studies and in several everyday applications such as sensors, permanent magnets, memory devices, and most recently, spintronic memories.
With improvements in thin film growth over the past few decades, the ability to control the structure of crystal lattices has also improved, to the extent that scientists can even force structures that are impossible in nature. The discovery of Ru’s ferromagnetic properties was facilitated by the use of ultra-thin films to force the ferromagnetic phase of the element. The details of the work are published in Nature Communications in a paper titled “Demonstration of Ru as the 4th ferromagnetic element at room temperature.” The University of Minnesota team comprised Dr. Patrick Quarterman, the lead author, Prof. Jian-Ping Wang, the corresponding author, and doctoral candidate Yang Lv.
Prof. Jian-Ping Wang says, “This work will trigger the magnetic research community to look into fundamental aspects of magnetism for many well-known elements.”
For Prof. Wang, the potential that lies beyond this development is obvious. “Magnetism is always amazing. It proves itself again. We are excited and grateful to be the first group to experimentally demonstrate and add the fourth ferromagnetic element at room temperature to the periodic table. It took us about two years to find a right way to grow this material and validate it. This work will trigger the magnetic research community to look into fundamental aspects of magnetism for many well-known elements.”
Co-author Paul Voyles, who is Beckwith-Bascom Professor and Chair of the Department of Materials Science and Engineering at the University of Wisconsin-Madison echoes Prof. Wang’s enthusiasm. “The ability to manipulate and characterize matter at the atomic scale is the cornerstone of modern information technology. Our collaboration with University of Minnesota Professor Wang’s group shows that these tools can find new things even in the simplest systems, consisting of a just a single element.”
Industry experts agree about the critical nature of the discovery. “Spintronic devices are of rapidly increasing importance to the semiconductor industry,” according to Todd Younkin, the director of Defense Advanced Research Projects Agency (DARPA)-sponsored consortia at Semiconductor Research Corporation (SRC). “Fundamental advances in our understanding of magnetic materials, such as those demonstrated in this study by Prof. Wang and his team, is critical to realizing continued breakthroughs in computing performance and efficiency.”
Collaborating scientists from Intel point to the possibilities that lie ahead. “Intel is pleased with the long-term research collaboration it has with the University of Minnesota and the C-SPIN Center. We are excited to share these developments enabled by exploring the behavior of quantum effects in materials, which may provide insights for innovative, energy efficient logic and memory devices.”
Novel technologies require novel materials
Magnetic recording is still the dominant player in data storage technology, but magnetic based random-access memory and computing is beginning to take its place. These magnetic memories place additional constraints on the magnetic materials where data is stored, compared to traditional hard disk media magnetic materials. This push for novel materials has led to renewed interest in attempts to realize predictions which show that under the right conditions, non-ferromagnetic materials such as Ru, palladium (Pd), and osmium (Os) can become ferromagnetic.
The discovery of ferromagnetism in Ruthenium has implications for the semiconductor industry
Building upon the established theoretical predictions, researchers at the University of Minnesota used seed layer engineering to force the tetragonal phase of Ru, which prefers to have a hexagonal configuration, and observed the first instance of ferromagnetism in a single element at room temperature. The crystal structure and magnetic properties were extensively characterized by collaborating with the University of Minnesota’s Characterization Facility and colleagues at the University of Wisconsin. The figure on the top left is a high resolution electron microscopy image confirming the tetragonal phase of Ru as predicted by the authors. (Image credit: University of Minnesota, Quarterman et al, Nature Communications)
From an application perspective, Ru is interesting because it is resistant to oxidation, and additional theoretical predictions claim it has a high thermal stability—a vital requirement for scaling magnetic memories. Examination of its high thermal stability is the focus of ongoing research at the University of Minnesota.
The lead author of the paper, Dr. Patrick Quarterman earned his doctoral degree under the guidance of Prof. Jian-Ping Wang. He is currently a National Research Council (NRC) postdoctoral fellow at the National Institute of Standards and Technology (NIST). In addition to Quarterman, Wang, and Voyles, researchers involved in this study include Javier Garcia-Barriocanal from the University of Minnesota Characterization Facility, Yang Lv from the University of Minnesota Department of Electrical and Computer Engineering, Mahendra DC from the University of Minnesota School of Physics and Astronomy, Sasikanth Manipatruni, Demitri Nikonov, and Ian Yang from Intel Components Research, and Congi Sun from the University of Wisconsin Department of Materials Science and Engineering.
Research was funded by the Center for Spintronic Materials, Interfaces and Novel Architectures (C-SPIN) at the University of Minnesota, the University of Minnesota Distinguished Doctoral Fellowship, and the National Science Foundation (NSF) through the NSF-funded Materials Research Science and Engineering Center at the University of Minnesota.
The full paper entitled “Demonstration of Ru as the 4th ferromagnetic element at room temperature,” by Quarterman et al, is available at the Nature Communications website.