Mesoscopic and Condensed Matter Physics

Biography

Biography: Elie A Moujaes

Abstract

The Ising effective field theory (EFT) method has proved to be a successful tool providing the appropriate exchange constants of basic ferromagnetic materials. In this work, Fe and Ni sublattice magnetizations of n-layered ultrathin iron-nickel alloy nanonjunctions [Fe1-cNic]n between Fe and Co leads, c being the Ni concentration inside the alloy, are inspected using a combination of EFT and mean field theory (MFT). Our EFT+MFT cocktail is believed to provide a simple yet accurate picture about the magnetizations, in complex ferromagnetic systems, through the calculation of parameters without the need to complicated theoretical models and in the absence of DFT results. For c < 0.4, the alloy has a bcc structure and becomes fcc otherwise. In the former case, the n layers of the alloy are connected to bcc Fe leads, whereas in the latter case, fcc Co leads are used instead. The exchange constants J and sublattice magnetizations σ calculated through EFT alone, are considered basic ingredients for quantum transport properties across the nanojunctions; total magnetizations within each layer are also exploited. Such EFT-based results then feed MFT calculations for the nanojunction from the interface inwards. Interestingly, it was observed that for bcc nanojunctions, the shape of all magnetization curves is unique for all c and for any value of n. This completely changes for fcc nanojunctions where differences are spotted for various concentrations. Special attention is given to the invar (c=0.5) and permalloy (c=0.81) alloys where some kind of saturation occurs when layers n ≥2 are constructed.