Sublattice magnetizations of ultrathin alloy [Co1−cGdc]n nanojunctions between Co leads using the combined effective field theory and mean field theory methods

Abstract

The cobalt and gadolinium sublattice magnetizations of ultrathin cobalt-gadolinium alloy nanojunctions [Co1−cGdc]n between Co leads are investigated using the effective field theory (EFT) and mean field theory (MFT) methods. The n hcp atomic layers at homogeneous concentrations c are considered to model structurally the alloy nanojunction. In particular, the Ising EFT serves to determine the appropriate exchange constants for Co and Gd, characterized by their fundamental spins, by calculating their single-site spin correlations, magnetizations, and Curie temperatures, in good agreement with experimental data in the ordered phase. The EFT results seed the MFT calculations for the nanojunction from the interface inwards. The combined EFT and MFT analysis yields the sublattice magnetizations for the Co and Gd sites, and compensation effects, on the individual layers of the nanojunctions, as a function of concentration, temperature, and nanojunction thickness. We observe that these magnetic variables are different for the first few layers near the nanojunction interfaces but tend to limiting solutions in the core layers. The exchange constants and sublattice magnetizations calculated by this combined approach and referenced to the fundamental Co and Gd spins, are necessary elements for the self-consistent analysis of the spin dynamics of the system and the quantum transport of lead magnons across the nanojunctions.