Browsing by Subject "Fe16N2"

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    Giant Saturation Magnetization Fe16N2 Thin Film
    (2018-04) Zhang, Xiaowei
    High saturation magnetization (Ms) material has always been a focus for many applications either in industry or academia. Fe16N2 has been a candidate since its first high Ms discovery in 1972. Does it have high Ms or not? This has been a question for the past five decades. Conventional magnetometer measures the magnetic moment of the iron nitride sample and yield its Ms by dividing the volume of the film, which both contain errors during experiments. A unique facing target sputtering system is used to fabricate epitaxial Fe16N2 thin film. To better measure the magnetic properties of Fe16N2 thin film, I use polarized neutron reflectivity (PNR), which directly detects the magnetization of the film in the depth profile. And the Ms of our film measured by PNR shows high Ms (up to 2500 emu/cm3), which is significantly higher than that of FeCo alloy. I studied the thermal stability of Fe16N2 thin films on MgO and GaAs substrate by elevating the temperature of the films. Despite the strain differences due to the substrate and seed layer, Fe16N2 thin film reserves its crystallinity and magnetic properties under 250 °C. One unaddressed physics related with Fe16N2 is how to understand its Mössbauer Spectroscopy. M. Takahashi and his co-authors, found three sets of hyperfine field splitting were linked to the low Ms of the sample, which was based on the assumption that the hyperfine field of iron is proportional to its magnetic moment. To resolve this “low Ms” issue, I conducted Mössbauer experiment and proposed a model that explains well the high Ms nature of Fe16N2 to understand the unique “high moment but low hyperfine field” predicament. If Fe16N2 is to be used in magnetic writer in hard drive, it needs to have lower anisotropy and lower saturation field. In the present work, Fe16N2 was modified with carbon dopant. With ~ at. 5% carbon addition in the film, I observed the existence of high Ms and low saturation field at the same time upon the appropriate amount of nitrogen in the film.
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    Magnetic properties and potential applications of Fe16N2
    (2021-02) Hang, Xudong
    Fe16N2 is a magnetic material with giant saturation magnetization that has potential applications in the hard drive and permanent magnet industries. In this thesis, fundamental magnetic properties of Fe16N2 are studied experimentally on thin-film samples and the potential application of Fe16N2 as a rare-earth-free permanent magnet is investigated theoretically. For the experimental part, the sputtering growth of Fe16N2 thin films on nonmagnetic seed layers is reported first, which provides the foundation for determining the magnetic structure of Fe16N2. The magnetic structure of high-magnetization Fe16N2, solved using polarized neutron diffraction, is reported for the first time. The magnetic structure also helps understand the origin of the giant magnetization observed in Fe16N2. Using the techniques of polarized neutron reflectometry, transmission electron microscopy, and vibrating sample magnetometry, we clarified the origin of the interface enhanced magnetization and perpendicularly magnetized components in Fe16N2 thin films. For the theoretical part, Monte Carlo methods were applied to explore the possibilities of antiferromagnet-ferromagnet exchange- coupled composite magnets, using Fe16N2 as the ferromagnet as it has large saturation magnetization and a reasonably high magnetic anisotropy constant. A new Monte Carlo-sampling based algorithm for comparative analysis of coercivity is proposed. It is confirmed that, with proper choice of an antiferromagnetic material and an optimized microstructure, large coercivity can be achieved in antiferromagnet-Fe16N2 composite magnets and that the maximum energy product can be enhanced by up to 10% as compared to pure iron nitride magnets.
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    Saturation magnetization of iron sixteen nitrogen two, a 40- year mystery
    (2012-03) Ji, Nian
    While the material α”-Fe16N2 and its interesting magnetic behavior were discovered decades ago, there is still no unified answer to the question on whether this phase has a giant saturation magnetization (Ms). There are three important “missing pieces” that emerge upon examination of the magnetization and discussing the magnetism of this system 1) There is lack of direct measure of the saturation magnetization on Fe16N2. Conventional magnetometer-based (VSM or SQUID) methods can only measure the total magnetic moment of the samples. The evaluation of the Ms value involves the challenging estimation of the thin film sample volume and the subtle assessment of magnetic contributions from underlayers, substrates or possible impurity phases, resulting in unpredictable errors. 2) There is no convincing theory/model to rationalize the existence of giant Ms. The conventional band theory based first-principles calculations only predicts an Ms value similar to that of pure Fe. 3) There is lack of experiments to explore the underlying physics of the magnetism in Fe16N2 from an electronic state viewpoint l. The previous investigations only focus on the saturation magnetization measurement. Fundamental physics experiments using advanced tools such as polarized neutron and synchrotron x-rays were seldom reported, which may provide unique and independent information on understanding the magnetism in this material system. On the purpose of addressing these three issues mentioned above. We first picked up a unique facing-target sputtering approach to synthesize Fe16N2 epitaxial thin films. A detailed structure and chemical analysis confirmed the crystallinity and epitaxial quality of fabricated Fe16N2 films. In terms of magnetic characterization, in addition to systematically study the saturation magnetization of the prepared films using a vibrating sample magnetometer (VSM) based method., for the first time,we have discovered the partial localization behavior of 3d electrons in Fe16N2 thin film samples by using polarized synchrotron x-rays. Furthermore, we have used polarized neutron reflectometry (PNR) to directly measure the saturation magnetization in absolute unit, which confirms the presence of giant saturation magnetization. The observed saturation magnetization of Fe16N2 phase is up to 2500 emu/cm3, which is significantly larger than that of the currently known limit (Fe65Co35 with saturation magnetization of 1900 emu/cm3) To understand the origin of the giant magnetization, we proposed a “cluster + atom” model, which pointeded out a possible scenario to develop this unusual magnetism in this Fe-N system. Synchrotron x-ray experiments also provided supporting evidences of the charge transfer from the itinerant iron atom to the Fe6N cluster, which is consistent with the proposed model. We further discussed the perpendicular anisotropy and the relatively large spin polarization ratio of these Fe16N2 films, which will be very useful for future magnetoresistive devices with perpendicular anisotropy and low damping constant.