Optimization of L1 FePt/Fe45Co55 thin films for rare earth free permanent magnet applications

Abstract

The magnetic properties of magnetron sputtered bilayers consisting of Fe45Co55 ultrathin layers on top of L10 FePt films epitaxially grown on MgO substrates are studied in view of their possible application as rare earth free permanent magnets. It is found that FePt layers induce a tetragonal distortion to the Fe-Co layers which leads to increased anisotropy. This allows to take advantage of the Fe-Co high magnetic moment with less significant loss of the coercivity compared to a typical hard/soft exchange spring system. A maximum energy product approaching 50 MGOe is obtained for a FePt(7 ML)/FeCo/(5 ML) sample. The results are in accordance with first-principles computational methods, which predict that even higher energy products are possible for micromagnetically optimized microstructures.

Optimum thickness of soft magnetic phase in FePt/FeCo permanent magnet superlattices with high energy product and large magnetic anisotropy energy

“…We use ab initio calculations to understand the atomic structure as well as magnetic anisotropy in such systems and focus on FePt/FeCo superlattices as thin films of FePt/Fe, FePt/Co, and FePt/FeCo have been realized 4,5 and a high value of 54 MGOe for the energy product has been obtained 11 for aligned and exchange-coupled FePt based films. Also a similar value of 50 MGOe has been obtained 5 for films with 5 monolayers (ML) of FeCo on 7 ML of FePt. 60 Pt 40 /Co bilayers.…”

“…A key figure of merit is the maximum energy product (BH) max = µ 0 M s 2 /4, where M s is the saturation magnetization and µ 0 is the permeability. RE based magnets SmCo 5 and Nd 2 Fe 14 B have a high energy product 2,3 of 31 MGOe and 50 MGOe, respectively but the value for RE free magnets is generally lower. Here we report from calculations a high value (up to ∼97 MGOe) of (BH) max for FePt/FeCo exchange coupled superlattices and show that the optimal thickness of the soft magnetic phase to achieve high magnetization as well as large magnetic anisotropy energy (MAE) is less than ∼2 nm.…”

Domain state modulation by interfacial diffusion in FePt/FeCo thin films: experimental approach with micromagnetic modelling

“…FeCo is the best chosen soft ferromagnetic material to couple with FePt due to its high saturation magnetization of 2.4 T [23,24], low anisotropy ∼4 × 10 4 J m −3 [25,26] and high Curie temperature [27,28]. The exchange-coupled FePt/FeCo bilayer thin films are the most stimulating magnetic multilayers in terms of distinctive properties such as large saturation magnetization, high coercivity and hence a high energy product retaining a high thermal stability as well [29,30]. The switching field here is reduced by varying the thickness of FeCo layer.…”

Rare-earth-free magnetically hard ferrous materials

“…2c . 61 These discoveries clearly show the potential applications of FeCo alloys in permanent magnets. In 2014, the interstitial boron doped FeCo, introduced by Khan and Hong, indicated that the magnetocrystalline anisotropy constant can reach 0.8 MJ m −3 with an estimated energy product of 100 MGOe.…”