Micromagnetic Modelling of the Dynamics of Exchange Springs in Multi-Layer Systems

Abstract

Exchange springs are formed in multilayers of alternating hard and soft ferromagnetic materials which are exchange coupled at their interfaces. These systems are rich of interesting physical properties, which can be tuned by selecting suitable geometries and compositions. In this paper, we present a computational study of the dynamics of a tri-layer DyFe 2 YFe 2 DyFe 2 exchange spring system near the bending field (the field required to twist the magnetization of the soft YFe 2 layer out of the aligned state). The dynamical reaction of the system to small variations of the applied field is studied and its oscillatory nature is analyzed numerically. The behaviors of the decay times, the frequencies, and amplitudes reveal enhanced responses of the system near the bending field.Index Terms-Dysprosium alloys, exchange springs, finite-element method, magnetic layered films, magnetic multilayers, micromagnetism, Nmag, numerical analysis, yttrium alloys.

A Systematic Approach to Multiphysics Extensions of Finite-Element-Based Micromagnetic Simulations: Nmag

“…One dimension, higher order elements Fig. 2(left) shows the equilibrium magnetization configuration for a toy model resembling the system studied in [11]. Our system consists of an x-directed stack of three films of equal thickness.…”

“…Parameters (in simulation units) for this example are (for interpretation, see [11] Fig. 3 shows the equilibrium M y component for atomic species A and C, computed on a coarse 1-d 'mesh' of 33 sites, once using first-order elements, and once using second-order elements.…”

Spin-polarized currents in exchange spring systems

“…The system materials are chosen in the following way: YFe 2 for the soft layer and DyFe 2 for the two hard layers. This choice allows us to study the system with a model similar to the one used in our previous work [9]. Regarding the geometry, the diameter of the cylindrical nano-pillar is 10 nm, while the thicknesses of the hard and soft layers are 5 and 40 nm, respectively.…”

“…The configuration of dysprosium is modeled by another magnetization field M Dy which is defined over the hard layers only. The model is similar to the one-dimensional model used in [9], extended to three dimensions (the stray field is calculated using the hybrid FEM/BEM method [10,11]). We also consider the same temperature (100 K) and the same material parameters: the moment densities of iron (in both DyFe 2 and YFe 2 ) and dysprosium are M Fe = 0.55 × 10 6 A/m and M Dy = 1.73 × 10 6 A/m, respectively; the easy axes for the anisotropy are u 1 = (0, 1, 1)/ √ 2, u 2 = (0, −1, 1)/ √ 2 and u 3 = (1, 0, 0), and the coefficients are K 1 = 33.9 × 10 6 J/m 3 , K 2 = −16.2 × 10 6 J/m 3 , K 3 = 16.4 × 10 6 J/m 3 .…”

Ultrafast Optical Parametric Pumping of Magnetization Reorientation and Precessional Dynamics inDyFe2/YFe2Exchange Springs

“…Exchange spring multilayers are of great interest for high density [2,3] and heat assisted magnetic recording [4], while antiferromagnetically coupled RFe 2 (R denotes rareearth metal) multilayers exhibit tunable coercivity [5,6] and giant magnetoresistance [7]. Ferromagnetic resonance has been measured and simulated in ferromagnetically coupled [8,9] and antiferromagnetically coupled [10] exchange springs, while microwave assisted switching has been simulated [11,12]. However, the parametric excitation of exchange springs by ultrafast optical pulses has not been explored.…”