MgO overlayer thickness dependence of perpendicular magnetic anisotropy in CoFeB thin films

Lam, D. D.; Bonell, Frédéric; Miwa, Shinji; Shiota, Yoichi; Yakushiji, Kay; Kubota, Hiroshi; Nozaki, Takayuki; Fukushima, Akio; Yuasa, Shinji; Suzuki, Y.

doi:10.3938/jkps.62.1461

Cited by 25 publications

(18 citation statements)

References 19 publications

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“…This process induces atomic intermixing phenomenon at interfaces, allowing for a larger MDL with increasing annealing temperatures. However, simultaneously, the B out-diffusion from the CoFeB also led to the enhancement of CoFeB crystallization, corresponding to the increased M S [21]. As previously mentioned, a relatively thin CoFeB layer experienced the PMA degradation at 450°C, while a relatively thick CoFeB maintained the dominant PMA features at the same annealing temperature (shown in Supplementary Figs.…”

Section: Resultsmentioning

confidence: 67%

“…Clear PMA behaviors were observed for the samples with CoFeB thickness up to 1.7 nm and the transition behavior to in-plane magnetic anisotropy (IMA) appeared when the t CFB was thicker than 1.8 nm. As previously reported, [18,20,21] the maximum CoFeB thickness ensuring the PMA features in a typical Ta/CoFeB/MgO frame was approximately 1.3 nm without an inter-layer exchange coupling. Therefore, a noticeable PMA observation at a 1.7 nm thick CoFeB layer would enable a flexible production margin in practical industrial applications when a thick CoFeB is available in the fabrication process.…”

Section: Methodsmentioning

confidence: 59%

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Highly stable perpendicular magnetic anisotropies of CoFeB/MgO frames employing W buffer and capping layers

Lee

Yang

et al. 2015

Acta Materialia

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Section: Resultsmentioning

confidence: 67%

Section: Methodsmentioning

confidence: 59%

Highly stable perpendicular magnetic anisotropies of CoFeB/MgO frames employing W buffer and capping layers

Lee

Yang

et al. 2015

Acta Materialia

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“…Although 3 nm MgO is too thick for practical use in MTJs, it was chosen to ensure continuity of the MgO layers and lessen the influence of the layers beyond it. [10,14,15] (Measurements of similar samples with 1 nm of MgO on both sides of the magnetic layer yielded the same trends. )…”

mentioning

confidence: 79%

Influence of Ta insertions on the magnetic properties of MgO/CoFeB/MgO films probed by ferromagnetic resonance

Sabino

Lim

Tran

2014

Appl. Phys. Express

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We show by vector network analyzer ferromagnetic resonance measurements that low Gilbert damping α, down to 0.006, can be achieved in perpendicularly magnetized MgO/CoFeB/MgO thin films with ultrathin insertions of Ta in the CoFeB layer. Although increasing the number of Ta insertions allows thicker CoFeB layers to remain perpendicular, the effective areal magnetic anisotropy does not improve with more insertions, which come with an increase in α.Perpendicular magnetic anisotropy (PMA) is the key to further downscaling of spin transfer torque magnetoresistive random memory devices, as it allows two key requirements to be satisfied: low critical current I c0 and high thermal stability ∆, the latter of which is proportional to the energy barrier E b between the two stable magnetic states. The spin torque switching efficiency, defined as E b /I c0 , is commonly used as a metric to account for both requirements. For a StonerWohlfarth model, it is given by [1] ( /4e) · (η/α), where α is the Gilbert damping parameter, and η is the spin polarization factor, which is related to the tunnel magnetoresistance ratio (TMR) by η = [TMR(TMR + 2)] 1/2 /[2(TMR + 1)]. It thus becomes evident that for high switching efficiency, one has to decrease α while keeping TMR high. Magnetic tunnel junctions (MTJs) based on CoFeB/MgO systems are well known to provide high TMR [2] and have recently been shown to possess PMA, which is attributed to the CoFeB/MgO interface.[3] A Ta layer is usually placed adjacent to the CoFeB to induce the proper crystallization necessary for PMA and high TMR [4]. In Ta/CoFeB/MgO systems, however, spin pumping to the Ta increases α.[5] Moreover, the CoFeB layer also needs to be ultrathin (typically less than 1.5nm) in order to exhibit PMA. [3] To improve the thermal stability as devices are scaled down to smaller diameters, increasing the effective areal anisotropy energy density K e f f t is desired.One approach to address these issues is the use of double-MgO structures, i.e., those in which both the barrier layer and capping layer straddling the free layer are made of MgO. Improved I c0 and/or ∆ have been reported in devices using double MgO free layers. [6,7,8,9] The improvement in thermal stability is attributed to the additional CoFeB/MgO interface, whereas lower I c0 is associated with low α. Indeed, α down to 0.005 has been measured in in-plane MgO/FeB/MgO films,[10] which agrees with device measurements.[11] The stacks investigated in these damping studies, however, did not have the Ta layer used in practical free layers with perpendicular anisotropy. [9,12] In addition, although the interfacial anisotropy in the out-of-plane devices measured by Tsunegi et al.[11] can be as high as 3.3 mJ/m 2 , the effective perpendicular anisotropy was rather low (K e f f t ≈ 0.04mJ/m 2 ) relative to that of a Ta/CoFeB/MgO stack [3]. In this work, we explore the influence of Ta insertions within the CoFeB layer of MgO/CoFeB/MgO films by magnetometry and vector network analyzer ferromagnetic resonance (VNA-...

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“…With very thin MgO (less than 1 nm), we believe that some Ta diffuses from the capping layer through MgO and reduces K I [8]. Indeed, 1 nm thick MgO is expected to be amorphous, which possibly favour the Ta diffusion.…”

Section: Resultsmentioning

confidence: 99%

“…Several studies tried to optimize the PMA and to clarify its origin by studying its dependence on the thickness of the magnetic layer [2][3][4], on the buffer layer [4], the oxidation condition at the interface [5][6][7] and the annealing temperature. We have also reported the MgO overlayer thickness dependence of the PMA, and found that the PMA strongly depends on the MgO overlayer thickness [8]. However, the variation of the PMA with the composition of CoFeB alloys [9] has not been fully investigated experimentally, and such a study may help us to understand the mechanism of PMA in CoFeB thin films.…”

Section: Introductionmentioning

confidence: 97%

Composition Dependence of Perpendicular Magnetic Anisotropy in Ta/Co_xFe_80-xB₂₀/MgO/Ta (x=0, 10, 60) Multilayers

Lam¹,

Bonell²,

Miwa³

et al. 2013

Journal of Magnetics

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The perpendicular magnetic anisotropy of sputtered CoFeB thin films covered by MgO was investigated by vibrating sample magnetometry. Three different Co x Fe 80-x B 20 alloys were studied. Under out-of plane magnetic field, the saturation field was found to increase with increasing the Co content. The magnetization and interface anisotropy energy were obtained for all samples. Both showed a marked dependence on the MgO overlayer thickness. In addition, their variations were found to be non-monotonous as a function of the Co concentration.

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MgO overlayer thickness dependence of perpendicular magnetic anisotropy in CoFeB thin films

Cited by 25 publications

References 19 publications

Highly stable perpendicular magnetic anisotropies of CoFeB/MgO frames employing W buffer and capping layers

Highly stable perpendicular magnetic anisotropies of CoFeB/MgO frames employing W buffer and capping layers

Influence of Ta insertions on the magnetic properties of MgO/CoFeB/MgO films probed by ferromagnetic resonance

Composition Dependence of Perpendicular Magnetic Anisotropy in Ta/Co_xFe_80-xB₂₀/MgO/Ta (x=0, 10, 60) Multilayers

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MgO overlayer thickness dependence of perpendicular magnetic anisotropy in CoFeB thin films

Cited by 25 publications

References 19 publications

Highly stable perpendicular magnetic anisotropies of CoFeB/MgO frames employing W buffer and capping layers

Highly stable perpendicular magnetic anisotropies of CoFeB/MgO frames employing W buffer and capping layers

Influence of Ta insertions on the magnetic properties of MgO/CoFeB/MgO films probed by ferromagnetic resonance

Composition Dependence of Perpendicular Magnetic Anisotropy in Ta/CoxFe80-xB20/MgO/Ta (x=0, 10, 60) Multilayers

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Composition Dependence of Perpendicular Magnetic Anisotropy in Ta/Co_xFe_80-xB₂₀/MgO/Ta (x=0, 10, 60) Multilayers