Transition Metal Dopants Essential for Producing Ferromagnetism in Metal Oxide Nanoparticles

Lydia M. Johnson, Boise State University
Aaron Thurber, Boise State University
Josh Anghel, Boise State University
Maryam Sabetian, Boise State University
Mark H. Engelhard, Pacific Northwest National Laboratory
Dmitri A. Tenne, Boise State University
Charles B. Hanna, Boise State University
Alex Punnoose, Boise State University

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This is an author-produced, peer-reviewed version of this article. The final, definitive version of this document can be found online at Physical Review B, published by American Physical Society. Copyright restrictions may apply. DOI: 10.1103/PhysRevB.82.054419

Abstract

Recent claims that ferromagnetism can be produced in nanoparticles of metal oxides without the presence of transition metal dopants have been challenged in this work by investigating 62 high quality well-characterized nanoparticle samples of both undoped and Fe doped (0-10% Fe) ZnO. The undoped ZnO nanoparticles showed zero or negligible magnetization, without any dependence on the nanoparticle size. However, chemically synthesized Zn_1-xFe_xO nanoparticles showed clear ferromagnetism, varying systematically with Fe concentration. Furthermore, the magnetic properties of Zn_1-xFe_xO nanoparticles showed strong dependence on the reaction media used to prepare the samples. The zeta potentials of the Zn_1-xFe_xO nanoparticles prepared using different reaction media were significantly different, indicating strong differences in the surface structure. Electron paramagnetic resonance studies indicate that the difference in the ferromagnetic properties of Zn_1-xFe_xO nanoparticles with different surface structures originates from differences in the fraction of the doped Fe ions that participate in ferromagnetic resonance.