Enhancement of magnetism of Fe that occurs by alloying with Cr or V is discussed on the basis of first-principles electronic structure calculation. The d states of Fe next to Cr(V) are pushed down to the lower energy side compared to those of pure Fe due to the hybridization with Cr(V) d states, which leads a Co-like electronic structure for the Fe atom. This enhances magnetic moments of other Fe atoms and also the exchange couplings among them. The same mechanism works as well for the

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... of Fe/Cr heterostructures. The idea is extended to design of a new type of antiferromagnets with high N\'eel temperature. Such heterostructures could be used to increase a magnetic anisotropy of permanent magnets.