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

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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.