Fabrication of $\hbox{Fe}_{16}\hbox{N}_{2}$ Films by Sputtering Process and Experimental Investigation of Origin of Giant Saturation Magnetization in $\hbox{Fe}_{16}\hbox{N}_{2}$

Abstract

We present a systematic study to address a longstanding mystery in magnetic materials and magnetism, whether there is giant saturation magnetization in Fe 16 N 2 and why. Experimental results based on sputtered thin film samples are presented. The magnetism of Fe 16 N 2 is discussed systematically from the aspects of material processing, magnetic characterization and theoretical investigation. It is observed that thin films with Fe 16 N 2 + Fe 8 N 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.

Effects of alloying and strain on the magnetic properties of Fe16N2

“…10 The spin moment on the 4d site reaches m i = 3.11μ B in QSGW , though we do not observe any obvious charge transfer from 4d to 4e and 8h sites in QSGW , relative to the LDA. Hence, we can not attribute the enhancement of M to the charge transfer as suggested by others [11][12][13] . Density of states (DOS) calculated within LDA and QSGW are shown in Fig.…”

“…Lai et al 10 included electronic correlations within LDA + U and found an enhanced magnetization M = 2.85μ B /Fe. Wang et al [11][12][13] identified a localized Fe state coexisting with the itinerant states in x-ray magnetic circular dichroism (XMCD) measurements. They introduced a specific charge transfer between different Fe sites and obtained a large M in LDA + U .…”

Formation and Decomposition of Metastable α′′‐Fe16N2 from in situ Powder Neutron Diffraction and Thermal Analysis

“…Additionally, even the theoretically predicted maximum values were surpassed. [13] However, the magnetic properties of αЈЈ-Fe 16 N 2 were a topic of debate ever since, partly due to the fact that it is difficult to prepare pure samples -best single phase bulk material presented so far contained 90.7 wt % of the target material, according to Rietveld refinements on powder X-ray diffraction data. [14] Very recently, a report claiming the successful single phase synthesis of αЈЈ-Fe 16 N 2 according to Mößbauer spectroscopy data was presented.…”

Preparation of an α″‐Fe16N2 Magnet via a Ball Milling and Shock Compaction Approach

“…[2][3][4] One of the more promising candidates is a 00 -Fe 16 N 2 , which possesses both giant saturation magnetization and a large magnetocrystalline anisotropy constant. [5] The a 00 -Fe 16 N 2 phase was first discovered by Jack, [6] but its magnetic properties remained unexplored until 1972 when Kim and Takahashi [7] reported its high magnetization in films, which was obtained by evaporating iron onto a glass substrate in low-pressure nitrogen. This discovery has inspired many groups all over the world to explore the material by using different preparation methods, mainly on thin film growth.…”

“…This discovery has inspired many groups all over the world to explore the material by using different preparation methods, mainly on thin film growth. [5,[7][8][9][10][11] a 00 -Fe 16 N 2 thin film with high Ms has potential applications in the magnetic recording field. Besides the thin film investigation, many groups are working on a 00 -Fe 16 N 2 powder preparation, [12][13][14][15][16] which could be used for permanent magnet preparation.…”