Search for a new bulk ferromagnet with controlling interatomic distance and valence electron number

3d过渡金属合金的磁化强度与成分的关系可用斯莱特-鲍林曲线很好地描述。用刚性能带模型解释这一行为，价电子数起着至关重要的作用，在Fe和Co之间的体心立方合金中达到最大值。高压实验还发现，3d体心立方合金的磁化强度随着压力的增加而减小，即原子间距离减小。因此，在电子数26附近出现高磁化强度的材料是可能的，并且具有比常压下更大的晶格常数。获得较大原子间距的直接方法是利用外延生长技术。相反，本项目将间隙原子，如氮或碳，引入体心立方陶瓷基质中，希望能生产出块状材料。我们采用的方法是：将FeFe-N或Fe-C的高温相淬火至室温，冷却至4.2K，通过马氏体相变，在9.6at的Fe-N合金上施加35T的强磁场，使其转变为具有铁磁性的BET结构。%N时，BET相的体积分数增加到91%，自发磁化强度从零磁场下的160emu/g提高到215emu/g。120℃的热处理使其部分转变为“α”相，但未观察到巨磁化迹象.Fe-C系也发生了磁场诱导马氏体相变，但磁化强度比Fe-N系小.为了改变Fe-N合金中的3d电子数，我们用Fe取代了Fe，但未能产生单一的γ相.

Composition dependence of magnetization for the 3d transition metal alloys is well described with the Slater-Pauling curve. The valence electron number plays an essentially important role to explain this behavior with the rigid band model and the highest value is attained in bcc alloys between Fe and Co. It is also known through high pressure experiments that magnetization of 3d bcc alloys decreases with increasing pressure, i. e., decreasing interatomic distance. Therefore, it is plausible to appear a high magnetization material at vicinity of electron number of 26 and with a larger lattice constant than at ambient pressure. The straight way to access the larger interatomic distance is to utilize epitaxial growth technique. But, instead, present project introduces interstitial atoms, such as nitrogen or carbon, into bcc matrix with a hope to produce bulk material. The method we employed is described in following sentences ; the high temperature phase of fee Fe-N or Fe-C is quenched to room temperature, and cooled to 4. 2K in order to transform them into bet structure with ferroiagnetism via the Martensitic transformation, fith application of high magnetic field of 35 T on the Fe-N alloy with 9. 6 at. %N, volume fraction of the bet phase increased to 91 % and attained spontaneous magnetization of 215 emu/g from 160 emu/g for zero magnetic field. Heat treatment at 120C partially transforms it into α" phase, but no indication of giant magnetization was observed. The magnetic field induced Martensitic transformation also took place in the Fe-C system, but resulted in smaller magnetization than Fe-N system. We substituted Mn for Fe in Fe-N alloy with aim of changing 3d electron number, but failed to produce single phase of γ.