Perpendicular-anisotropy CoFeB-MgO magnetic tunnel junctions with a MgO/CoFeB/Ta/CoFeB/MgO recording structure

Sato, Hideo; Yamanouchi, Michihiko; Ikeda, Shoji; Fukami, Shunsuke; Matsukura, F.; Ohno, Hideo

doi:10.1063/1.4736727

Cited by 270 publications

(163 citation statements)

References 31 publications

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“…[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-FMR) measurements.…”

mentioning

confidence: 99%

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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mentioning

confidence: 99%

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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“…The structure exhibits a moderate K eff ∼ 0.2 MJ m −3 , due to the competition between interface and shape anisotropy associated with the sizable magnetization. K eff can often be improved by introducing a second CoFeB/MgO interface in more complicated MgO/CoFeB/Ta/CoFeB/MgO structures [4]. Nevertheless, it has been shown that even the optimized MTJ structure is unstable for dimensions below 30 nm [5].…”

Section: Introductionmentioning

confidence: 99%

Structure, site-specific magnetism, and magnetotransport properties of epitaxial D022 -structure Mn2FexGa thin

et al. 2017

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Ferrimagnetic Mn 2 Fe x Ga (0.26 x 1.12) thin films have been characterized by x-ray diffraction, magnetometry, x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and Mössbauer spectroscopy with the aim of determining the structure and site-specific magnetism of this tetragonal, D0 22 -structure Heusler compound. High-quality epitaxial films with low root-mean-square surface roughness (∼0.6 nm) are grown by magnetron cosputtering. The tetragonal distortion induces strong perpendicular magnetic anisotropy along the c axis with a typical coercive field μ 0 H ∼ 0.8 T and an anisotropy field ranging from 6 to 8 T. On increasing the Fe content x, substantial uniaxial anisotropy, K u 1.0 MJ m −3 , can be maintained over the full x range, while the magnetization of the compound is reduced from 400 to 280 kA m −1 . The total magnetization is almost entirelygiven by the sum of the spin moments originating from the ferrimagnetic Mn and Fe sublattices, with the latter being coupled ferromagnetically to one of the former. The orbital magnetic moments are practically quenched and have negligible contributions to the magnetization. The films with x = 0.73 exhibit an anomalous Hall angle of 2.5% and a Fermi-level spin polarization above 51%, as measured by point contact Andreev reflection. The Fe-substituted Mn 2 Ga films are tunable with a unique combination of high anisotropy, low magnetization, appreciable spin polarization, and low surface roughness, making them strong candidates for thermally stable spin-transfer-torque switching nanomagnets with lateral dimensions down to 10 nm.

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“…This is the first time that low switching current (45% decrease) and high interfacial PMA have been achieved simultaneously with double oxidation interfaces [50]. The same year, Sato et al [51] investigated MTJ with MgO/CoFeB/Ta/CoFeB/MgO free layer containing double CoFeB/MgO interfaces, which exhibited high thermal stability and comparable threshold currents. The thickness of Ta spacer layer was designed as 0.4 nm for the top and bottom CoFeB layers to form large enough exchange coupling, enabling the simultaneous STT switching of the two layers.…”

Section: Structure Optimization: Double Cofeb/mgo Interfacesmentioning

confidence: 99%

Tunnel Junction with Perpendicular Magnetic Anisotropy: Status and Challenges

et al. 2015

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Magnetic tunnel junction (MTJ), which arises from emerging spintronics, has the potential to become the basic component of novel memory, logic circuits, and other applications. Particularly since the first demonstration of current induced magnetization switching in MTJ, spin transfer torque magnetic random access memory (STT-MRAM) has sparked a huge interest thanks to its non-volatility, fast access speed, and infinite endurance. However, along with the advanced nodes scaling, MTJ with in-plane magnetic anisotropy suffers from modest thermal stability, high power consumption, and manufactural challenges. To address these concerns, focus of research has converted to the preferable perpendicular magnetic anisotropy (PMA) based MTJ, whereas a number of conditions still have to be met before its practical application. This paper overviews the principles of PMA and STT, where relevant issues are preliminarily discussed. Centering on the interfacial PMA in CoFeB/MgO system, we present the fundamentals and latest progress in the engineering, material, and structural points of view. The last part illustrates potential investigations and applications with regard to MTJ with interfacial PMA.

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Perpendicular-anisotropy CoFeB-MgO magnetic tunnel junctions with a MgO/CoFeB/Ta/CoFeB/MgO recording structure

Cited by 270 publications

References 31 publications

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

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

Structure, site-specific magnetism, and magnetotransport properties of epitaxial D022 -structure Mn2FexGa thin

Tunnel Junction with Perpendicular Magnetic Anisotropy: Status and Challenges

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