Strong coercivity reduction in perpendicular FePt∕Fe bilayers due to hard/soft coupling

Casoli, F.; Albertini, F.; Nasi, L.; Fabbrici, S.; Cabassi, R.; Bolzoni, F.; Bocchi, C.

doi:10.1063/1.2905294

Cited by 94 publications

(65 citation statements)

References 17 publications

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“…In agreement with the HRTEM investigations, this small change can be explained by only marginal metallic Fe remaining on top of FePt, as most of the iron is present in oxidized state. In this case, the properties are consistent with the film being in the rigid magnet regime 47 where due to exchange coupling the spin orientation in a soft magnetic Fe layer does not deviate from the FePt spin direction. 33 Schematically, this is illustrated in the respective sketch in Fig.…”

supporting

confidence: 67%

“…In experiments and calculations, the critical thickness of the Fe layer for the transition from rigid magnet to exchange spring magnet regime in Fe/FePt composites is reported to be around 2-3 nm. 33,47 After immersion of the Fe-O/Fe/FePt composite film in 1M KOH and application of −1.26 V and −0.18 V, strong voltage-induced changes of the magnetic hysteresis are observed (Fig. 5).…”

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confidence: 99%

“…The structural data obtained by FFT allow to identify the iron oxide as Fe 3 The oxidized state, exhibiting an Fe/FePt bilayer with 2 nm Fe layer thickness, is at the critical point for the transition from rigid magnet to exchange spring magnet behaviour. 33,47 This allows to discuss the observed large voltage-induced changes in anisotropy by a combination of MI effects at the Fe-O/Fe surface with exchange coupling at the Fe/FePt interface. As discussed for single Fe-O/Fe films, voltage-induced reduction and oxidation will cause a variation of the metallic Fe layer thickness.…”

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confidence: 99%

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Research Update: Magnetoionic control of magnetization and anisotropy in layered oxide/metal heterostructures

et al. 2016

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Electric field control of magnetization and anisotropy in layered structures with perpendicular magnetic anisotropy is expected to increase the versatility of spintronic devices. As a model system for reversible voltage induced changes of magnetism by magnetoionic effects, we present several oxide/metal heterostructures polarized in an electrolyte. Room temperature magnetization of Fe-O/Fe layers can be changed by 64% when applying only a few volts in 1M KOH. In a next step, the bottom interface of the in-plane magnetized Fe layer is functionalized by an L10 FePt(001) underlayer exhibiting perpendicular magnetic anisotropy. During subsequent electrocrystallization and electrooxidation, well defined epitaxial Fe3O4/Fe/FePt heterostructures evolve. The application of different voltages leads to a thickness change of the Fe layer sandwiched between Fe-O and FePt. At the point of transition between rigid magnet and exchange spring magnet regime for the Fe/FePt bilayer, this induces a large variation of magnetic anisotropy.

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confidence: 67%

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confidence: 99%

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confidence: 99%

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Research Update: Magnetoionic control of magnetization and anisotropy in layered oxide/metal heterostructures

et al. 2016

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“…As a soft magnetic layer, Fe is a commonly employed material, because of its small magnetocrystalline anisotropy and large saturation magnetization. [54][55][56][57][58][59][60][61] Different bilayer stacks as well as more complex ECC structures like trilayers 62 were proposed, and their magnetic properties dependent on the soft layer thickness were investigated, [63][64][65] demonstrating the superior performance of ECC media.…”

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confidence: 99%

Review Article: FePt heat assisted magnetic recording media

Weller¹,

Parker²,

Mosendz³

et al. 2016

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

159

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Heat-assisted magnetic recording (HAMR) media status, requirements, and challenges to extend the areal density (AD) of magnetic hard disk drives beyond current records of around 1.4 Tb/in.2 are updated. The structural properties of granular high anisotropy chemically ordered L10 FePtX-Y HAMR media by now are similar to perpendicular CoCrPt-based magnetic recording media. Reasonable average grain diameter ⟨D⟩ = 8–10 nm and distributions σD/D ∼ 18% are possible despite elevated growth temperatures TG = 650–670 °C. A 2× reduction of ⟨D⟩ down to 4–5 nm and lowering σD/D < 10%–15% are ongoing efforts to increase AD to ∼4 Tb/in.2. X = Cu ∼ 10 at. % reduces the Curie temperature TC by ∼100 K below TC,bulk = 750 K, thereby lowering the write head heat energy requirement. Multiple FePtX-Y granular layers with Y = 30–35 vol. % grain-to-grain segregants like carbides, oxides, and/or nitrides are used to fully exchange decouple the grains and achieve cylindrical shape. FePt is typically grown on fcc MgO (100) seedlayers to form well oriented FePt (002). A FePt lattice parameter ratio c/a ∼0.96 and high chemical order S > 0.90 result in magnetic anisotropy KU ∼ 4.5 × 107 erg/cm3, and only 25% below the FePt single crystal value KU = 6.6 × 107 erg/cm3 has been achieved in 7–8 nm diameter grains. Switching field distributions depend on anisotropy field (HK) distributions, which are currently of the order of ΔHK/HK ∼ 10% (ΔHK ∼ 10–12 kOe, HK ∼ 10–11 T) at room temperature. High thermal conductivity heat sink layers, including Ag, Au, Cu, and Cr, are used to optimize the cooling rate and maximize the down- and cross-track thermal gradient, which determines the achievable track density.

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“…[8][9][10][11][12] In permanent magnetism, randomly oriented anisotropy axes reduce the maximum energy product (BH) max to somewhat more than one fourth of the "aligned" value. Thus, the (BH) max values obtained for isotropic nanocomposite magnets thus far are limited to about 25 MGOe [200 kJ/m 3 ], which is about 40% of the best aligned Nd 2 Fe 14 B-type magnets.…”

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confidence: 99%

Aligned and exchange-coupled FePt-based films

Liu

George

Skomski

et al. 2011

Applied Physics Letters

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Two-phase nanostructures of hard L10-ordered FePt and soft iron-rich fcc Fe-Pt are investigated experimentally and by model calculations. The Fe-Pt thin films were produced by epitaxial co-sputtering onto MgO and have a thickness of about 10 nm. They form two-phase dots that cover a large fraction of the surface but are separated from each other. X-ray diffraction and TEM show that the c-axis of the phase FePt is aligned in the direction normal to the film plane. The experimental and theoretical hysteresis loops indicate archetypical exchange coupling, and excellent magnetic properties are obtained. The largest values of coercivity, saturation magnetization, and nominal energy product obtained in the samples studied are 51 kOe, 1287 emu/cc, and 54 MGOe, respectively.

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Strong coercivity reduction in perpendicular FePt∕Fe bilayers due to hard/soft coupling

Cited by 94 publications

References 17 publications

Research Update: Magnetoionic control of magnetization and anisotropy in layered oxide/metal heterostructures

Research Update: Magnetoionic control of magnetization and anisotropy in layered oxide/metal heterostructures

Review Article: FePt heat assisted magnetic recording media

Aligned and exchange-coupled FePt-based films

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