[Back]

A.V. Ruban, S. Khmelevskyi, P. Mohn, B. Johansson:
"Magnetic state, magnetovolume effects, and atomic order in Fe₆₅Ni₃₅ Invar alloy: A first principles study\";
Physical Review B, 76 (2007), 0144201 - 0144209.

We employ the locally self-consistent Green´s function technique and exact muffin-tin orbital method to
investigate magnetic state and ground state properties of Invar Fe65Ni35 alloy. We show that it is in a chemically
disordered state, characterized by a relatively small amount of atomic short-range order, above the
magnetic ordering temperature. We speculate that it should remain in this state below the Curie temperature
upon applying usual heat treatment for the Invar alloys. The magnetic state at the experimental lattice spacing
is shown to be sensitive to the type of approximation for the exchange-correlation functional: While the
magnetic ground state is purely ferromagnetic in the generalized gradient approximation, there is a small
amount of Fe atoms with magnetic moment antiferromagnetically aligned relative to the global magnetization
in the local density approximations. The local spin-density approximation, however, fails to yield correctly the
equilibrium lattice spacing, whereas the generalized gradient approximation reproduces it reasonably well. The
anomalous spontaneous volume magnetostriction leading to the Invar effect is found to be approx. 3%, in fair
agreement with the experimental estimate of approx. 2.2%.\