New Ruthenium Oxides: Compounds Poised between Magnetic and Non-magnetic Ground States R. J. Cava, Princeton University, DMR Figuring out the ways that the chemistry and crystal structure of a chemical compound join with the laws of physics to give rise to the electronic and magnetic properties of matter is one of the grand challenges in solid state chemistry. For no compounds is the understanding of this problem more of a challenge than for transition metal oxides, where subtle differences in structure and chemistry often lead to big differences in properties. Our research has shown that Ruthenium-based oxides are uniquely interesting in this context, because they often stand exactly at the borderline between different kinds of electronic and magnetic behavior. The figure shows one of the new compounds discovered in this work, NaLi 2 Ru 6 O 12 : RuO 6 octahedra (light blue) form an array that creates triangular tunnels containing Li and hexagonal tunnels containing Na. The origin of the non-magnetic behavior of this compound is not yet understood.

All of today’s electronics technologies, ranging from IPods to medical imaging systems, are based on chemical compounds whose properties are critical to making the technologies work. These compounds have been discovered and developed over decades of basic and applied research in solid state and materials chemistry. The success of future electronics technologies depends on our continuing to develop new compounds with more and more complex and sophisticated properties. Revolutionary developments in new electronic materials in the recent past (such as high temperature superconductors) have shown that our understanding of how the properties of electronically conducting and magnetic compounds depend on their structure and chemistry is surprisingly poor. This project directly addresses one of the major deficiencies in our current understanding; that is: What are the critical chemical and structural factors that cause some chemical compounds to be magnetic, while others, though quite similar, are not? Through the study of one particularly rich class of compounds, ruthenium-based oxides, which straddle the border between magnetism and non-magnetism, we have made substantial progress toward understanding that relationship, and have uncovered new compounds with unexpected magnetic behavior that are of great interest to materials physicists. New Ruthenium Oxides: Compounds Poised between Magnetic and Non-magnetic Ground States R. J. Cava, Princeton University, DMR

Science and Engineering Expo, Princeton University, March 2005 The Expo was dedicated to capturing the imaginations of students in middle school, a period when many students lose interest in science. This photo shows the PI explaining magnetism to students by showing the magnetic field lines around a permanent magnet with iron filings sprinkled on paper. New Ruthenium Oxides: Compounds Poised between Magnetic and Non- magnetic Ground States R.J. Cava, Princeton University DMR

The Science and Engineering Expo at Princeton in the Spring of 2005 was designed to capture the imaginations of middle school students. It is believed that middle school is a critical time in a student’s education – when many of them lose interest in science and no longer consider careers in science and engineering. More than 1000 middle school students from local schools came to Princeton for the Expo. Particularly emphasized were hands-on activities and demonstrations. The PI of this research project demonstrated the magnetic properties of materials to diverse audiences of middle school students in small groups. Of particular interest to the students was the surprising way that magnetic force can act through a distance. Magnetic field lines can be illustrated nicely through the use of a soft magnetic material in fine particle form spread out on a piece of white paper over permanent magnets in different configurations (the photograph). Students were particularly impressed with seeing the magnetic bits on credit card strips and in observing the penetration of the magnetic fields from strong permanent magnets (neodymium iron boron) through their hands. The Expo was widely covered by local news media. A Web site that shows all the activities can be found at: Science and Engineering Expo, Princeton University, March 2005