Tetragonal equilibrium states of Mn and Fe

Abstract

Tetragonal equilibrium states of Mn and Fe have been found by total-energy calculations at constant volume as a function of c/a with the full-potential linearized-augmented-plane-wave method using two different potentials: (1) the local-spin-density approximation without relativistic corrections and (2) the Perdew-Burke-Ernzerhof exchange-correlation potential in a generalized-gradient approximation with relativistic corrections. Comparison of potential (1) with potential (2) shows that the energy curves relative to the lowest minimum of each are very similar and have minima at the same c/a values. However, potential (2) makes the magnetic phases more magnetic. Both Mn and Fe are shown to have stable and metastable tetragonal equilibrium states in each of several magnetic phases. The antiferromagnetic (AF) energy versus c/a curve of Mn shows a stable tetragonal state at c/a = 0.96, close to the experimental value for γ-Mn at c/a = 0.95, and a metastable body-centered-tetragonal state at c/a = 0.60. However the bcc state at c/a = 0.707 is inherently unstable. The calculation on Fe in tetragonal structure shows that AF Fe has a tetragonal equilibrium state at c/a = 1.08, and ferromagnetic Fe has a tetragonal equilibrium state at c/a = 1.17. © 2000 American Institute of Physics.