Development and Application of Self-interaction Correction in First-principles Electronic Structure Calculations to Design New Materials for Spintronic Devices

豊田 雅之  (物理)

Abstract

The electronic structures and magnetic properties of dilute magnetic
semiconductors (DMS) are investigated by using computational simulations
based on first-principles calculations and model calculations. Two
improvements in the simulation methods are proposed and implemented, in
order to discuss the following effects in DMS systems: i) the
self-interaction error in the LDA exchange-correlation functional and
ii) the inhomogeneous distribution of transition-metal atoms. To
overcome the self-interaction error in the LDA calculations, we have
developed a new scheme of the self-interaction-corrected local density
approximation (SIC-LDA) for KKR-CPA band structure calculations. The
density-of-states spectra calculated within SIC-LDA are generally in
good agreement with experimental photoemission spectroscopy data, while
the experimentally observed high-Curie-temperature in the wide band-gap
DMS such as (Ga,Mn)N and (Zn,Co)O is not expected from the SIC-LDA
results. One possible explanation for the discrepancy is the
inhomogeneous distribution of transition-metal atoms. For this problem,
the simulations of spinodal decomposition are performed. The results
show that the Curie temperature of wide band-gap DMS system can be
increased by making a connected cluster of transition-metal atoms, if
the impurity concentration is high ($15 \sim 20$ \%, for example).