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Enhancement of Magnetism of Fe by Cr and V
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Enhancement of Magnetism of Fe by Cr and V


Strong, permanent magnets are extremely important in contemporary industrial applications. They play an essential role in many kinds of electrical products, and they are particularly important for hybrid and electric vehicles. When the magnet is stronger, then the energy efficiency for these vehicles becomes better, and this increased efficiency is helpful given our longstanding concerns regarding the availability of fossil fuels and the effect of emissions on global warming.


The fundamental characteristics which are necessary for industrial-grade permanent magnets are large saturation magnetization, high critical temperature, and strong coercive force. So far, for various reasons, Co and Ni have been key players in the production of strong permanent magnets. However, we should pay attention to the fact that Fe has the largest amount of saturation magnetization among the single component magnetic materials; consequently, we should seek the possibility of inventing strong permanent magnets composed of Fe. Furthermore, the abundance of Fe is much larger than the abundance of either Co or Ni, and hence it is less expensive.


Recently, M. Ogura, H. Akai, and J. Kanamori theoretically pointed out that the magnetism of Fe is enhanced in Fe-Cr and Fe-V alloys.[1] The majorityspin d states of a Fe atom adjacent to Cr or V are pushed down by the hybridization with the minorityspin d states of Cr or V (Fig. 1).



Fig.1 Change in the electronic structure of Fe due to the hybridization of d states with those of Cr. (by M. Ogura et al. Ref. 1).


The majority-spin d states of Fe are then fully occupied and the electronic structure becomes like that of Co. It has long been known that in a Fe-Co alloy, saturation magnetization and the Curie-Temperature increase due to the interactions between Fe and Co atoms. The ��Co-like Fe atoms�� in Fe-Cr and Fe-V alloys are expected to play a similar role.


The coupling between the Fe atom and Cr or V atom is antiferromagnetic, and it gives rise to a decrease in the saturation magnetization. On the other hand, it also gives rise to an anisotropy which results in a strong coercive force in some special hetero-structures. Therefore, the present study suggests the possibility of inventing strong permanent magnets without using rare earth metals.




[1] M. Ogura, H. Akai, and J. Kanamori, J. Phys. Soc. Jpn. 80 (2011) 104711.

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