Density-functional investigation of magnetism inδ-Pu

Abstract

We present density-functional results of $\ensuremath{\delta}$-Pu obtained from three electronic-structure methods. These methods have their individual strengths and are used in combination to investigate the magnetic and crystal stability of $\ensuremath{\delta}$-Pu. An all-electron, full potential linear muffin-tin orbitals (FPLMTO) method, that includes corrections for spin-orbit coupling and orbital-polarization effects, predicts $\ensuremath{\delta}$-Pu to be an antiferromagnet at zero temperature with a volume and a bulk modulus in very good agreement with experiment. The site-projected magnetic moment is smaller than expected $(\ensuremath{\sim}1.5{\ensuremath{\mu}}_{B})$ due to large cancellation of spin and orbital moments. These calculations also predict a mechanical instability of antiferromagnetic (AF) $\ensuremath{\delta}$-Pu. In addition, techniques based on the Korringa-Kohn-Rostoker (KKR) method within a Green's-function formalism and a projector augmented wave (PAW) method predict the same behavior of $\ensuremath{\delta}$-Pu. In order to study disordered magnetism in $\ensuremath{\delta}$-Pu, the KKR Green's-function technique was used in conjunction with the disordered local-moment model, whereas for the FPLMTO and PAW methods this was accomplished within the special quasirandom structure model. While AF $\ensuremath{\delta}$-Pu remains mechanically unstable at lower temperatures, paramagnetic $\ensuremath{\delta}$-Pu is stabilized at higher temperatures where disordered magnetic moments are present and responsible for the crystal structure, the low density, and the low bulk modulus of this phase.