Materials World Network: Targeting New Complex Itinerant Magnets Using Experiment and Theory

Iowa State University, Ames IA

Investigators

Abstract

TECHNICAL SUMMARY This Materials World Network project,supported by the Solid-State and Materials Chemistry program and the Office of Special Programs in the Division of Materials Research, combines synthesis, diffraction, magnetization measurements with first principles electronic structure theory to design and understand new intermetallic ferromagnets and antiferromagnets. Experimental activity will focus on complex 4d and 5d metal-boride frameworks with magnetic 3d elements, e.g., Cr-Ni, inserted in voids to create magnetic structures with low-dimensional character. The metal-boride framework is a structurally strong, electronically robust, and provides a mechanism for magnetic exchange between adjacent magnetic metal atoms via the spins on the conduction electrons. Previous support focused on structures with four-fold symmetry; new discoveries expand our studies to six-fold and three-fold symmetry, in which frustration effects can influence magnetic behavior. Specifically, atomic and magnetic structures will be determined by X-ray and neutron diffraction as well as magnetization experiments. Electronic structure theory will probe the energetics of various atomic and magnetic structures by evaluating orbital and exchange interactions to establish chemical rules and to calculate transition temperatures for ferromagnetic or antiferromagnetic behavior. Theoretical results will provide feedback for subsequent synthetic targets with predicted magnetic behavior. Theory will also investigate the magnetic structures and characteristics of the simpler MM'P and MM'As (M, M' = V-Cu), which also show tetragonal and trigonal symmetries. This work will establish the generality of the theoretical approach. At present, no general chemical rules exist to target compounds with permanent magnetic behaviour. The successful outcome will establish the evolution of magnetic behavior within a single structural family to identify trends in magnetic behavior as various chemical and physical parameters change in systematic ways. NON-TECHNICAL SUMMARY This scientific effort combines experiment and theory to design and prepare new magnets belonging to a recently discovered family of metal-rich compounds. The complexity of these compounds allows chemical tuning, that can be accomplished by synthesis and can be studied by quantum chemistry. From this systematic study of a chemical family of compounds, a new set of rules will emerge for targeting metallic, permanent magnets, which have numerous technological applications. The real challenge will be to predict, via theory, the temperature range at which such targeted materials will show permanent magnetic behavior. The scientific effort will provide students a truly interdisciplinary problem, by combining chemistry and physics with experiment and theory. The student participants will clearly learn how different scientific subjects and approaches impact other scientific areas. The student participants from Aachen, Germany and Ames, Iowa will have opportunities for exchange, and they will learn both experimental and theoretical components of research in solid-state chemistry. In summary, this effort represents a strong, synergistic coupling of experiment and theory that will identify and characterize new magnetic materials, with the broader goal of establishing predictive rules for building newer magnets.