Longitudinal Spin Fluctuations and Magnetic Ordering Temperature in Metals: First-Principle Modeling and Phase Space Integration Measure

Abstract

In magnetically ordered metals the magnitude of the local atomic moment become temperature dependent. To deal with this problem on the ab-initio level one need to employ a specific methodology for calculation of the electronic structure that takes into the account the magnetic disorder effects. In addition one needs to setup a special statistical models allowing simultaneously for ab-initio mapping and for the variation of the local spin magnitude. To this end here we discuss and employ methodology that is based on the Disordered Local Moment (DLM) formalism, spin-constraint Local Spin Density Approximation (LSDA) and Lichtenstein theorem for calculation of the inter-site exchange interactions. An extended classical Heisenberg Hamiltonian used for mapping allows for the variation of the lattice site spin magnitude. We consider here three representative canonical transition metals ferromagnets hcp Gd, bcc Fe and fcc Ni with quite a different character of the magnetic moment localization and illustrate the relative importance of the longitudinal spin fluctuations and the magnetic disorder induced electronic structure reconstruction. We use recently introduced linear measure [1] for integration over the longitudinal spin component in the classical configurational spin space.