Exchange coupling and magnetic anisotropy at Fe/FePt interfaces

Abstract

We perform fully relativistic first principles calculations of the exchange interactions and the magnetocrystalline anisotropy energy (MAE) in an Fe/FePt/Fe sandwich system in order to elucidate how the presence of Fe/FePt (soft/hard magnetic) interfaces impacts on the magnetic properties of Fe/FePt/Fe multilayers. Throughout our study we make comparisons between a geometrically unrelaxed system and a geometrically relaxed system. We observe that the Fe layer at the Fe/FePt interface plays a crucial role inasmuch its (isotropic) exchange coupling to the soft (Fe) phase of the system is substantially reduced. Moreover, this interfacial Fe layer has a substantial impact on the MAE of the system. We show that the MAE of the FePt slab, including the contribution from the Fe/FePt interface, is dominated by anisotropic inter-site exchange interactions. Our calculations indicate that the change in the MAE of the FePt slab with respect to the corresponding bulk value is negative, i.e., the presence of Fe/FePt interfaces appears to reduce the perpendicular MAE of the Fe/FePt/Fe system. However, for the relaxed system, this reduction is marginal. It is also shown that the relaxed system exhibits a reduced interfacial exchange. Using a simple linear chain model we demonstrate that the reduced exchange leads to a discontinuity in the magnetisation structure at the interface.

Multiscale modeling of current-induced switching in magnetic tunnel junctions using ab initio spin-transfer torques

“…The atomic resolution allows systems where the typical micromagnetic models break down (e.g., where atomically staggered magnetic order is present) to be investigated. While currently some parameters, such as the exchange interaction and the anisotropy, are inferred from experiments, those can also be taken from ab initio calculations of the actual MTJ stack with atomic resolution [20,23]. Computational feasibility may ultimately limit the size of treatable systems and the accessible time scales; however, this prototypical MTJ study is still far from these limits, suggesting a range of realistic magnetic multilayered devices (including some accounts for disorder) to be well within the scope of the method.…”

Implementation of non-collinear spin-constrained DFT calculations in SIESTA with a fully relativistic Hamiltonian

“…sin , 0, cos 2,4 ), our generalized Heisenberg model gives: J zz and J xz can be obtained by mapping this function to the set of (q n , q ( ) E n n ) pairs obtained by means of CDFT calculations. Figure 4 plots the results.…”

“…A deep understanding of the magnetic properties is crucial, and requires a combination of experiments, theory, and modeling. In most magnetic materials, the arrangement of the atomic magnetizations adopt a collinear(CL) configuration in which a common direction is shared by all of them(usually taken as the z axis) [1,2]. Specifically, each individual magnetization can be parallel or antiparallel to each other, leading to ferromagnetic(FM) or antiferromagnetic(AFM) phases, respectively.…”

Influence of the structure defects on the magnetic properties of the FePt/Fe bilayer

“…Recently a plenty of theoretical studies have been done [17], [18], [19] and a number of experiments has been performed on FePt-based systems such as exchangecoupled L1 0 FePt/[Co/Ni] N [20], FePt/[Co/Pt] [21], FePt/Fe 3 Pt [6] nanocomposite multilayers, FePt/CoCrNi [22], FePt/FeRh [23], FePt/CoFeTaB [24] bilayers, FePt thin films on Si [25] and CrV [26] substrate, FePt nanoparticles [27], [28], FePt/Fe thin films [29], [30], [31], [32], [33], [34]. Among them, FePt/Fe system has shown unique magnetic values.…”