Laser MBE-grown CoFeB epitaxial layers on MgO: Surface morphology, crystal structure, and magnetic properties

Кавеев, А. К.; Bursian, V. E.; Кричевцов, Б. Б.; Mashkov, Konstantin V.; Волков, М. П.; Tabuchi, Masao; Sokolov, N. S.

doi:10.1103/physrevmaterials.2.014411

Cited by 12 publications

(6 citation statements)

References 36 publications

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“…The free layer is typically a thin body-centered cubic (bcc) CoFeB layer with an interface to MgO, which creates a large tunneling magnetoresistance. [2,3,4] The required thermal stability for long term data storage is achieved through interface perpendicular magnetic anisotropy with adjacent MgO layers on both interfaces. [3,4] Ultrathin W and Ta insertion layers can further increase the perpendicularly magnetic anisotropy and thus lead to longer thermal stability.…”

Section: Main Textmentioning

confidence: 99%

“…), ln is the log in base e, and 𝑎𝑎 is the lattice constant of the thin film; a=0.287 nm for CoFeB [2]. We can determine the prefactor 𝜂𝜂 from Equation S1 by dividing the magnon density 𝑛𝑛 𝑚𝑚 (𝑇𝑇) by the argument of the Bloch law:…”

Section: Magnon Density and The Exchange Constants Of The Free Layermentioning

confidence: 99%

“…Jamileh Beik Mohammadi, 1 Bartek Kardasz, 2 Georg Wolf, 2 Yizhang Chen, 1 Mustafa Pinarbasi, 2 and Andrew D. Kent 1…”

Section: Supplementary Informationmentioning

confidence: 99%

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Reduced Exchange Interactions in Magnetic Tunnel Junction Free Layers with Insertion Layers

Mohammadi

Kardasz²,

Wolf³

et al. 2019

ACS Appl. Electron. Mater.

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Perpendicularly magnetized CoFeB layers with ultra-thin non-magnetic insertion layers are very widely used as the electrodes in magnetic tunnel junctions for spin transfer magnetic random access memory devices. Exchange interactions play a critical role in determining the thermal stability of magnetic states in such devices and their spin torque switching efficiency.Here the exchange constant of free layers incorporated in full magnetic tunnel junction layer stacks, specifically CoFeB free layers with W insertion layers is determined by magnetization measurements in a broad temperature range. A significant finding is that the exchange constant decreases significantly and abruptly with W insertion layer thickness. The perpendicular magnetic anisotropy shows the opposite trend; it initially increases with W insertion layer thickness and shows a broad maximum for approximately one monolayer (0.3 nm) of W. These results highlight the interdependencies of magnetic characteristics required to optimize the performance of magnetic tunnel junction devices.

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Section: Main Textmentioning

confidence: 99%

Section: Magnon Density and The Exchange Constants Of The Free Layermentioning

confidence: 99%

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Reduced Exchange Interactions in Magnetic Tunnel Junction Free Layers with Insertion Layers

Mohammadi

Kardasz²,

Wolf³

et al. 2019

ACS Appl. Electron. Mater.

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“…The Co 40 Fe 40 B 20 , MgO, Co, Ni, Fe 2 O 3 and Y 3 Fe 5 O 12 targets were ablated by pulsed radiation of a KrF excimer laser. The preparation of MgO (001) substrates was carried out as described by Kaveev et al (2018). The Fe 3 O 4 layers were grown on MgO at a substrate temperature of 673 K from an Fe 2 O 3 target.…”

Section: Methodsmentioning

confidence: 99%

Structural transformations and interfacial iron reduction in heterostructures with epitaxial layers of 3d metals and ferrimagnetic oxides

et al. 2018

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The present paper sheds light on the interfacial structural transformation taking place upon epitaxial growth of ferromagnetic 3d metal compounds -Co, Ni and CoFeB -on the surface of magnetically ordered iron oxides -Fe 3 O 4 , Fe 2 O 3 and Y 3 Fe 5 O 12 . The reducing conditions due to the excess of neutral metal atoms at the surface cause reduction of the Fe 3+ ions of the underlying iron oxide layer to the Fe 2+ state and subsequent recrystallization of the subsurface region to an MeO-like rock salt crystal structure. The corresponding change of the lattice symmetry can be readily recognized by in situ high-energy electron diffraction reciprocal-space mapping and ex situ X-ray diffraction techniques. From an analysis of diffraction and X-ray absorption data a tentative model of the structural transformation is proposed, based on penetration of Me atoms into the near-surface region of the iron oxide lattice. Once a few nanometre thick oxidized layer is formed, further growth of pure metallic film with native crystal structure takes place. An important observation made is that the oxidation/ reduction effects do not occur when 3d metals are deposited onto more stable MgO and Gd 3 Ga 5 O 12 surfaces. This circumstance makes it appropriate to propose these materials for use as buffer layers to prevent formation of antiferromagnetic monoxide transition regions in multilayered magnetic structures. The presented results are supposed valuable for development of hybrid ferromagnetic heterostructures attractive for various spintronic applications.

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“…interlayer, surface morphology, crystalline structure, properties of magnetic layers with local, site-specific domains. [30][31][32][33][34][35][36] Hence, various factors affect the characteristics of an MTJ stack in which TMR ratio strongly depends on how an electron is penetrated through the FM/MgO interfaces. The barrier height herein plays an important role which determines the electron transmission coefficient at the FM/MgO interfaces.…”

Section: Introductionmentioning

confidence: 99%

Tailoring sidewall profiles of magnetic tunnel junctions fabricated with various etching conditions

Hoang¹,

Vu²,

Cao³

et al. 2019

Jpn. J. Appl. Phys.

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Structural and compositional characteristics of MgO-based magnetic tunnel junctions were characterized using advanced transmission electron and focused-ion beam microscopies. These junctions were fabricated from two ferromagnetic layers separated by a dielectric one and have a switchable resistance that depends upon the relative magnetizations of those two ferromagnetic layers. Certain etching conditions were used to complete the fabrication process aiming to achieve sharp-edge profiles on either side of the pillars. Controlling the edge profiles of those fabricated pillars enables to avoid shortcuts that induce magnetoresistance effect. Not only structural properties of each layer in the MgO junction are characterized, but its compositional characteristics are also explored with electron energy loss spectroscopy, this aims to elucidate the role of elements existing in the given MgO structure. Results of this work are of technological interest since they provide a better understanding in the microstructural properties of the MgO-based magnetic tunnel junctions.

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Laser MBE-grown CoFeB epitaxial layers on MgO: Surface morphology, crystal structure, and magnetic properties

Cited by 12 publications

References 36 publications

Reduced Exchange Interactions in Magnetic Tunnel Junction Free Layers with Insertion Layers

Reduced Exchange Interactions in Magnetic Tunnel Junction Free Layers with Insertion Layers

Structural transformations and interfacial iron reduction in heterostructures with epitaxial layers of 3d metals and ferrimagnetic oxides

Tailoring sidewall profiles of magnetic tunnel junctions fabricated with various etching conditions

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