We present a systematic study to address a longstanding mystery in magnetic materials and magnetism, whether there is giant saturation magnetization in Fe16N2 and why. Experimental results based on sputtered thin film samples are presented. The magnetism of Fe16N2 is discussed systematically from the aspects of material processing, magnetic characterization and theoretical investigation. It is observed that thin films with Fe16N2+Fe8N mixture phases and high degree of N ordering, exhibit a saturation magnetization up to 2.68T at room temperature, which substantially exceeds the ferromagnetism limit based on the traditional band magnetism understanding. From X-ray magnetic circular Dichorism (XMCD) experiment, transport measurement and first-principle calculation based on LDA+U method, it is both experimentally and theoretically justified that the origin of giant saturation magnetization is correlated with the formation of highly localized 3d electron states in this Fe-N system. A large magnetocrystalline anisotropy for such a material is also discussed. Our proposed cluster+atom theory provides promising directions on designing novel magnetic materials with unique performances.
Bibliographical noteFunding Information:
The work was supported in part by the U.S. Department of Energy, Office of Basic Energy Sciences under contract No. DE-AC02-98CH10886, characterization facility of National Science Foundation the Minnesota MRSEC program under Award Number DMR-0819885, NSF NNIN program and University of Minnesota Supercomputing Institute. All the samples and testing experiments reported in this paper have been done before September 2009 (first report of our work at UMN MINT review 2009) based on above-mentioned financial support. The microscopy at HTML/ORNL was sponsored by U.S. DOE, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program. The authors are grateful to the useful discussion with Drs. Valeria Lauter, Chengjun Sun, Hailemariam Ambaye, and Steve M Heald from DOE national labs (ORNL, ANL) and Profs. Jack Judy, Paul Crowell, and Randall Victora from the University of Minnesota.
- X-ray magnetic circular dichorism
- giant saturation magnetization
- high magnetic moment
- magnetic head
- permanent magnet