Disorder-Induced Antiferromagnetic to Ferromagnetic Transition in Magnetic Overlayers: (Fe,Mn)/W(001) as a Case Study

Abstract

The magnetic phase stability of the random FexMn1-x monolayer on the bcc-W(001) substrate is studied from first-principles. The exchange interactions among two-types of magnetic atoms in the overlayer are estimated in the framework of the adiabatic approximation and used to construct the random classical two-dimensional Heisenberg Hamiltonian. The stability of such effective Hamiltonian is then studied with respect to a broad class of magnetic arrangements which include also possible spin-spiral structures. This allows to investigate a broader class of systems than in a conventional total energy search. We have found that exchange interactions between Fe-spin are antiferromagnetic while those between Mn-spins are ferromagnetic over the whole concentration range. This pronounced frustration leads to a complex behavior in which the c(2× 2) antiferromagnetic state for Fe-monolayer goes over to complex incommensurate spin-spiral magnetic structures with increasing Mn-content. A spin-spiral state with a large period was found also for the Mn-monolayer case in agreement with a recent experimental and theoretical study. [DOI: 10.1380/ejssnt.2010.184]