Large enhanced perpendicular magnetic anisotropy in CoFeB/MgO system with the typical Ta buffer replaced by an Hf layer

We report on the perpendicular magnetic anisotropy (PMA) behavior of heavy metal (HM)/ Fe alloy/MgO thin film heterostructures after an ultrathin HfO 2 passivation layer is inserted between the Fe alloy and the MgO. This is accomplished by depositing one to two atomic layers of Hf onto the Fe alloy before the subsequent rf sputter deposition of the MgO layer. This Hf layer is fully oxidized during the subsequent deposition of the MgO layer, as confirmed by X-ray photoelectron spectroscopy measurements. As the result a strong interfacial perpendicular anisotropy energy density can be achieved without any post-fabrication annealing treatment, for example 1.7 erg/cm 2 for the Ta/Fe 60 Co 20 B 20 /HfO 2 /MgO heterostructure. Depending on the HM, further enhancements of the PMA can be realized by thermal annealing to at least o 400 C . We show that ultra-thin HfO 2 layers offer a range of options for enhancing the magnetic properties of magnetic heterostructures for spintronics applications.

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“…200 C) annealing. [19][20][21] In the inset of Fig. 2(b), we also show the effective PMA energy density K eff for the series B …”

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Strong perpendicular magnetic anisotropy energy density at Fe alloy/HfO2 interfaces

Ralph

Buhrman

2017

Applied Physics Letters

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“…This suggests that the thin Ta layer may be amorphous, which is consistent with previous reports. 19,20 Another possibility for the lack of diffraction peaks is because they are beyond the limit of sensitivity of the x-ray diffraction instruments. The small critical switching current in the current-induced magnetization switching by spin-orbit torque of the Ta layer in these structures suggests that the β-Ta phase may exist in both as-deposited and annealed samples.…”

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confidence: 99%

Effect of annealing conditions on the perpendicular magnetic anisotropy of Ta/CoFeB/MgO multilayers

2016

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Films with a structure of Ta (5 nm)/Co20Fe60B20 (0.8–1.5 nm)/MgO (1 nm)/Ta (1 nm) were deposited on Corning glass substrates by magnetron sputtering. The as-deposited films with CoFeB layer thickness from 0.8 to 1.3 nm show perpendicular magnetic anisotropy (PMA). After annealing at a proper temperature, the PMA of the films can be enhanced remarkably. A maximum effective anisotropy field of up to 9 kOe was obtained for 1.0- and 1.1-nm-thick CoFeB layers annealed at an optimum temperature of 300 °C. A 4-kOe magnetic field was applied during annealing to study its effect on the PMA of the CoFeB layers. The results confirmed that applying a perpendicular magnetic field during annealing did not improve the maximum PMA of the films, but it did enhance the PMA of the thinner films at a lower annealing temperature.

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“…In MgO/CoFeB, it is thought to be the Fe-O hybridization at the interface that leads to the PMA 3 although a thin metallic capping layer, often Ta, has been shown to contribute also. 19,20 PMA has also been observed and studied in Co/Pd and Co/Pt multilayers, 21 but in these cases, it is the Co 3d-(Pd, Pt) 5d hybridization that is understood to induce the PMA. 22,23 While the data presented here indicate an interfacial origin of the PMA in CFMS thin films, samples with different interfaces were prepared in order to understand which interface is important.…”

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Perpendicular magnetic anisotropy in Co2Fe0.4Mn0.6Si

Ludbrook

Ruck

Granville

2016

Journal of Applied Physics

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We report perpendicular magnetic anisotropy (PMA) in the half-metallic ferromagnetic Heusler alloy Co 2 Fe 0.4 Mn 0.6 Si (CFMS) in a MgO/CFMS/Pd trilayer stack. PMA is found for CFMS thicknesses between 1 and 2 nm, with a magnetic anisotropy energy density of K U = 1.5 × 10 6 erg/cm 3 for t CFMS = 1.5 nm. Both the MgO and Pd layer are necessary to induce the PMA. We measure a tunable anomalous Hall effect, where its sign and magnitude vary with both the CFMS and Pd thickness.A magnetic thin film will generally prefer to have its magnetic moment lying in the plane of the sample owing to the large demagnetizing field. New magnetic devices have made it desirable to fabricate thin magnetic layers which instead have an easy axis of magnetization directed perpendicular to the film plane, a condition known as perpendicular magnetic anisotropy (PMA). 1 In particular, spin-transfer-torque (STT) based devices require that a magnetic free layer can be easily flipped by a spin-polarized current while maintaining a high stability against thermal fluctuations. 2 Magnetic layers with PMA are well suited to optimize this trade-off for device applications.In order to realize a high efficiency STT device, a high degree of spin-polarization in the magnetic layers is also desirable. CoFeB, with approximately 65% spin polarization, has been the most widely studied material so far, because it can be grown with PMA and incorporated into device structures with very large tunneling magnetoresistance (TMR). 3 There is a strong motivation to incorporate a half-metallic ferromagnet (HMFM) with higher spin polarization in these devices, and Heusler alloys are promising in this regard. 4 In particular, Co 2 FeSi and Co 2 MnSi both have 100% spin polarization 5-7 and high Curie temperatures (c. 1000 • C). Recent studies have shown the intermediary compound Co 2 Fe x Mn (1−x) Si with x≈0.4 to be eminently promising for device applications with a low Gilbert damping parameter 8 and record 75% room temperature GMR ratio. 9 Efforts to induce PMA in the Heuslers have focused on compounds containing Fe on MgO (eg. Co 2 FeAl 10,11 ). This was guided by earlier studies of CoFeB/MgO where the PMA is thought to have its origin in the Fe-O hybridization. 3 PMA has recently been reported in Co 2 MnSi in CMS/Pd multilayer stacks on MgO, 12 and for Pd buffered Co 2 Fe x Mn 1−x Si on MgO, 13 but the details of the PMA and the contribution of the various interfaces remains unclear. Here, we demonstrate PMA in MgO/CFMS/Pd stacks, and show that both interfaces are important for this effect.Samples were grown by DC magnetron sputtering in a Kurt J Lesker CMS-18 UHV system with a base pressure of 2 × 10 −8 Torr. Multilayer stacks consisting of MgO(2)/CFMS(t CFMS )/Pd(2.5), where the number in parentheses is the nominal layer thickness in nm, were grown on 10 × 10mm Si/SiO 2 substrates at room temperature and post-growth annealed in-situ for 1 hour at 300 • C with an in-plane magnetic field of 170 Oe. MgO was RF sputtered with 100 W power in 3 mTorr Ar, giving a ...

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Large enhanced perpendicular magnetic anisotropy in CoFeB/MgO system with the typical Ta buffer replaced by an Hf layer

Cited by 162 publications

References 20 publications

Strong perpendicular magnetic anisotropy energy density at Fe alloy/HfO2 interfaces

Strong perpendicular magnetic anisotropy energy density at Fe alloy/HfO2 interfaces

Effect of annealing conditions on the perpendicular magnetic anisotropy of Ta/CoFeB/MgO multilayers

Perpendicular magnetic anisotropy in Co2Fe0.4Mn0.6Si

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