Department of Physics and Astronomy: Publications and Other Research
Date of this Version
2013
Document Type
Article
Citation
PHYSICAL REVIEW B 88, 054421 (2013)
Abstract
The effects of Gd doping and O vacancies on the magnetic interaction and Curie temperature TC of EuO are studied using first-principles calculations. Linear response calculations in the virtual crystal approximation show a broad maximum in the Curie temperature as a function of doping, which results from the combination of the saturating contribution from indirect exchange and a decreasing contribution from the f -d hopping mechanism. Non-Heisenberg interaction at low doping levels and its effect on TC are examined. The electronic structure of a substitutional Gd and of an O vacancy in EuO are evaluated. When the 4f spins are disordered, the impurity state goes from single to double occupation, but correlated bound magnetic polarons are not ruled out. At higher vacancy concentrations typical for Eu-rich EuO films, the impurity states broaden into bands and remain partially filled. To go beyond the homogeneous doping picture, magnetostructural cluster expansions are constructed, which describe the modified exchange parameters near Gd dopants or O vacancies. Thermodynamic properties are studied using Monte Carlo simulations. The Curie temperature for Gd-doped EuO agrees with the results of the virtual crystal approximation and shows a maximum of about 150 K. At 3.125% vacancy concentration the TC increases to 120 K, consistent with experimental data for Eu-rich film samples.
Comments
©2013 American Physical Society