Structural and Magnetic Properties in Sputtered Iron Oxide Epitaxial Thin Films-Magnetite Fe3O4 and Epsilon Ferrite ε-Fe2O3-
Structural and Magnetic Properties in Sputtered Iron Oxide Epitaxial Thin Films-Magnetite Fe3O4 and Epsilon Ferrite ε-Fe2O3-
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发表时间：
2019
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通讯作者：
Masato Watanabe
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作者：
Masato Watanabe
磁性铁氧化物，即所谓的铁氧体，由于其多才多艺的磁性[1，2]和主要成分铁和氧的大量自然丰度，已被用于各种电磁应用，这满足了当今社会对材料的需求，如无处不在的稀有金属。在种类繁多的铁氧体中，我们重点研究了两种具有独特磁性和电学功能的铁氧化物：磁铁氧体Fe_3O_4和表面型铁氧体ε-Fe_2O_3，并尝试用传统的溅射方法制备它们的外延生长薄膜，这是一种有利于工业器件应用的工艺。第一氧化铁的磁铁矿是一种普遍存在的磁性材料，自然作为铁砂的主要成分而被发现[3]。其晶体结构为反尖晶石结构，由四面体A位的Fe3+、八面体B位的Fe2+和Fe3+和氧位的Fe3+组成。它的室温饱和磁化强度为4πM，为6.25 kg，居里温度为858K[4]。磁铁矿还表现出半金属性[5-8]和大反常霍尔电阻率ρH~10-40μΩcm[9]的特征电学性质，这与钴基全豪斯勒化合物[10]相当，这使得各种自旋电子器件如磁隧道结(MTJ)成为可能。由于其高度的生物相容性，磁铁矿的生物医学应用，如热疗和药物输送系统(DDS)也得到了广泛的应用[11]。到目前为止，我们的研究小组对多晶磁铁矿薄膜中的少量元素添加进行了研究，发现某些元素的添加高达几个百分点，特别是Ge，提高了其热稳定性并导致磁化强度增加[12，13]。由于此类元素在磁铁矿外延薄膜中的作用尚未得到证实，因此我们在本研究中研究了少量Ge添加到磁铁矿外延薄膜中的结构和磁效应。
Magnetic iron oxides, so-called “ferrites”, have been utilized for various electromagnetic applications due to their versatile magnetic properties [1,2] and large natural abundance of main constituent iron and oxygen, which meets recent social requirements for materials such as rare-metal-free ubiquity. Among the huge variety of ferrites, we focused on two iron oxides: magnetite Fe3O4 and epsilon ferrite ε-Fe2O3, both of which show unique magnetic and electronic functionalities, and attempted to fabricate their epitaxially grown thin films by conventional sputtering, which is an advantageous process for industrial device applications. Magnetite of the first iron oxide is an ubiquitous magnetic material naturally found as the main component of iron sand [3]. Its crystal structure is an inverse spinel that is composed of Fe3+ at tetrahedral A sites, Fe2+ and Fe3+ at octahedral B sites and oxygen sites. It has a room temperature saturation magnetization 4πM of 6.25 kG, which is the highest among iron oxides, and Curie temperature TC of 858 K [4]. Magnetite also shows characteristic electronic properties of half-metallicity [5-8] and large anomalous Hall resistivity ρH ~10-40μΩcm [9], which is comparable with Co based full Heusler compounds [10], leading to the possibility for various spintronic devices such as magnetic tunnel junctions (MTJ). Due to its high biocompatibility, magnetite’s biomedical applications such as hyperthermia and drug delivery system (DDS) have also been pursued [11]. To date, our research group conducted research on small-amount element additions in polycrystalline magnetite films and found that the additions of some elements up to several percent, especially Ge, raised their thermal stability and caused an increase in magnetization [12,13]. Since the effects of such element additions in magnetite epifilms have not yet been confirmed, we studied the structural and magnetic effects on small-amount Ge addition to magnetite epifilms in this research.