Materials World Network: Designed preparation, characterization, magnetic properties and quantum chemical calculations of new complex itinerant magnets, Ti8-xM3+xRu18-yRhyB8 (M = Cr,Mn, Fe, Co, Ni; 0 less than x less than 2; 0 less than y less than 18)

• Applicant: Professor Dr. Boniface P. T. Fokwa
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: from 2008 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 73090861

This project combines theory and experiment towards the preparation, characterization and theoretical study of new complex transition metal borides which are potential magnets, i.e., ferromagnets, ferrimagnets or antiferromagnets. Magnetically active 3d metals occupying voids in complex metal boride frameworks give rise to low-dimensional structures of these magnetic metals, which may result in low-dimensional magnetic behavior. Experimental efforts will focus on the new intermetallic series, Ti8–xM3+xRu18–yRhyB8 (M = Cr, Mn, Fe, Co, Ni; 0 ≤ x ≤ 2; 0 ≤ y ≤18), in which the number of valence electrons can be varied by the Ru:Rh ratio. Since the number of valence electrons can be tuned, we anticipate inducing desired magnetic properties in these phases, with a particular focus on achieving itinerant ferrimagnetism, which is a rare magnetic property not yet observed in other complex borides. The new compounds will be structurally characterized, and their magnetic properties will be determined. Together with the experimental effort, theoretical determination of the electronic structures and interatomic magnetic (exchange) couplings for various models of these structures will provide feedback toward further synthetic efforts of new phases with targeted magnetic properties. Furthermore, theoretical work will establish a relationship between chemical bonding factors and local exchange interactions that dictate the magnetic structure in these cases and other itinerant magnets. Thus, the intellectural merit of this activity is to understand the relationship between chemical composition and magnetic behavior in intermetallic compounds, which will be accomplished through a synergistic engagement of experiment and theory. The broader impacts of the effort include establishing rules for synthetic chemists to search for new itinerant magnets with desired magnetic properties, as well as to identify chemical and physical signposts for ferromagnetism, ferrimagnetism and antiferromagnetism.This project is a close collaboration between solid-state chemistry groups at the Institute of Inorganic Chemistry at RWTH Aachen University and the Chemistry Department at Iowa State University (ISU). The Aachen group will extend its present synthetic experience using high-temperature methods to synthesize several compounds in this new series.Furthermore, they will characterize them using diffraction methods and EDX analyses, and measure their magnetic properties. Concurrently, the ISU group will use electronic structure packages, chemical bonding analyses and multiple scattering theories to understand the magnetic behavior of the synthesized phases and predict new synthetic targets for the Aachen group. In addition, the ISU group will carry out temperature-dependent single crystal studies to explore details in structural changes with magnetic behavior. For any ferromagnetic products, calorimetric measurements will also be conducted to explore their potential magnetocaloric effects, which is important for elucidating possible thermomagnetic applications. Likewise, both groups will clarify the spin structures of the new compounds by experimental (neutron diffraction) and theoretical (spin-polarized super-cell calculations) efforts.The combination of experiment and theory for condensed matter systems in this project provides graduate students a truly interdisciplinary problem – they will clearly learn how different scientific subjects and models impact other areas. The graduate students in this project in 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.

• DFG Programme: Research Grants
• International Connection: USA
• Participating Person: Professor Dr. Gordon J. Miller