Magnetic interactions in iron

A first-principles discrete variational method in the local density approximation is used to calculate the local properties at Fe sites in Fe(N,M) clusters representing alpha -iron. Here N and M are the respective numbers of antiferromagnetically coupled Fe atoms at the nearest neighbour (NN) and the next nearest neighbour (NNN) sites of the central atom. The local magnetic moment was found to increase slightly with N, reach a maximum and decrease with further N values. A large moment is obtained for N=0 and M=6. The magnitude of the magnetic hyperfine field was found to decrease linearly with increasing N for fixed M. The average quantities are also calculated treating the AFM atoms as impurities in the alpha -iron lattice. A model is presented which attempts to understand the coupling of the central atom to its NN and NNN as being accomplished through T_2g and E_g states respectively.