Theoretical investigations of the magnetic behaviour of Cr monolayers deposited on a Fe(001) substrate: Role of a mono-atomic step

In this paper we present a theoretical study of the magnetic properties of n Cr monolayers (ML) deposited on a Fe(001) substrate. We use the real space recursion method in a tight binding framework to determine the electronic structure of non-periodic systems involving a large number of inequivalent atoms. The aim of this work is to investigate the possibility to obtain a magnetic defect in the Cr layer by frustrating the plane to plane antiferromagnetic (AF) order. First, we study the magnetism of n perfect Cr monolayers (1 ≤ n ≤ 10) deposited on a perfect (001) Fe substrate and we show that a magnetic defect can be obtained for n ≥ 6 ML but it is clearly less stable than the solution without defect. We show also that, after the deposition of 3 Fe monolayers onto the Cr, the magnetic defect is obtained for much smaller Cr thicknesses ( n ≥ 2). Then, we consider a Fe substrate presenting a mono-atomic step. We study the magnetic moments distributions during the growth process of Cr monolayers assuming that the growth starts at the step. We show that (i) the perturbation due to the step is limited to the vicinity of the step and has a small extension in the plane of the Cr layers, and (ii) a wall is generated in the Cr layer by the step and splits clearly the Cr layer into two domains. Finally, we determine the structure of collinear walls in chromium and we discuss their role on the magnetic properties.