Nanoscale measurement of giant saturation magnetization in α″-Fe16N2 by electron energy-loss magnetic chiral dichroism

Xinfeng Chen; Soma Higashikozono; Keita Ito; Lei Jin; Ping-Luen Ho; Chu-Ping Yu; Nyan-Hwa Tai; Joachim Mayer; Rafal E Dunin-Borkowski; Takashi Suemasu; Xiaoyan Zhong

doi:10.1016/j.ultramic.2019.02.016

Nanoscale measurement of giant saturation magnetization in α″-Fe₁₆N₂ by electron energy-loss magnetic chiral dichroism

Ultramicroscopy. 2019 Aug:203:37-43. doi: 10.1016/j.ultramic.2019.02.016. Epub 2019 Feb 19.

Authors

Affiliations

¹ National Center for Electron Microscopy in Beijing, Key Laboratory of Advanced Materials (MOE), The State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China.
² Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan.
³ Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich GmbH, Jülich 52425, Germany.
⁴ National Center for Electron Microscopy in Beijing, Key Laboratory of Advanced Materials (MOE), The State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China; Department of Materials Science and Engineering, National Tsing-Hua University, Hsinchu 30013, Taiwan.
⁵ Department of Materials Science and Engineering, National Tsing-Hua University, Hsinchu 30013, Taiwan.
⁶ Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich GmbH, Jülich 52425, Germany; Central Facility for Electron Microscopy, RWTH Aachen University, Aachen 52074, Germany.
⁷ National Center for Electron Microscopy in Beijing, Key Laboratory of Advanced Materials (MOE), The State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China. Electronic address: xyzhong@mail.tsinghua.edu.cn.

PMID: 30862364
DOI: 10.1016/j.ultramic.2019.02.016

Abstract

Metastable α″-Fe₁₆N₂ thin films were reported to have a giant saturation magnetization of above 2200 emu/cm³ in 1972 and have been considered as candidates for next-generation rare-earth-free permanent magnetic materials. However, their magnetic properties have not been confirmed unequivocally. As a result of the limited spatial resolution of most magnetic characterization techniques, it is challenging to measure the saturation magnetization of the α″-Fe₁₆N₂ phase, as it is often mixed with the parent α'-Fe₈N phase in thin films. Here, we use electron energy-loss magnetic chiral dichroism (EMCD), aberration-corrected transmission electron microscopy, X-ray diffraction and macroscopic magnetic measurements to study α″-Fe₁₆N₂ (containing ordered N atoms) and α'-Fe₈N (containing disordered N atoms). The ratio of saturation magnetization in α″-Fe₁₆N₂ to that in α'-Fe₈N is determined to be 1.31 ± 0.10 from quantitative EMCD measurements and dynamical diffraction calculations, confirming the giant saturation magnetization of α″-Fe₁₆N₂. Crystallographic information is also obtained about the two phases, which are mixed on the nanoscale.

Keywords: Electron energy-loss magnetic chiral dichroism; Giant saturation magnetization; Rare-earth-free permanent magnetic materials; α″-Fe(16)N(2), high spatial resolution.