Effect of Seed Layer on Room Temperature Tunnel Magnetoresistance of MgO Barriers Formed by Radical Oxidation in IrMn-Based Magnetic Tunnel Junctions

Dahmani, F.

doi:10.1143/jjap.51.043002

Cited by 4 publications

(3 citation statements)

References 31 publications

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“…Moving the defect away from the interface reduces the P spin up transmission, and thus TMR, especially for the F center. This theoretical insight is compatible with the likely presence in experiments of oxygen vacancies at the lower MTJ interface when the MgO barrier is grown by oxidizing thin layers of metallic Mg deposited atop the lower ferromagnetic metallic electrode while avoiding the latter's oxidation [67,68]. It is also in line with the role of interfacial oxygen vacancies in promoting perpendicular magnetic anisotropy in the adjacent ultrathin ferromagnetic films [69,70] of MgO-class MTJs with perpendicular magnetization.…”

Section: Rotating the M Centersupporting

confidence: 83%

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Impact of single and double oxygen vacancies on electronic transport in Fe/MgO/Fe magnetic tunnel junctions

Taudul,

Bowen,

Alouani

2019

Preprint

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The combination of a low tunnelling barrier height and a large tunnelling magnetoresistance (TMR) ratio in MgO-class magnetic tunnel junctions has enabled next-generation information storage and bio-inspired computing solutions thanks to the spin transfer torque effect. Recent literature has proposed that this synergistic combination arises from the electronic properties of oxygen vacancies. To explicitly understand their impact on spin-polarized transport, we have computed the electronic and transport properties of single (F centers) and paired (M centers) oxygen vacancies using density functional theory and the projector augmented wave (PAW) method. These point defects can generate barrier heights as low as 0.4V for FeCo electrodes irrespective of the defect's spatial position within the barrier, and of the orientation of the M center. These defects promote a strong decrease in the conductance of the spin up channel in the MTJ's parallel (P) magnetic state that mainly accounts for an order-of-magnitude drop in TMR, from ≈10000% in the ideal case toward values more in line with experiment. When placed in the middle layer of the MgO barrier, the F center introduces additional P ↑ transmission away from the Γ point. This scattering lowers TMR to 145%. In contrast, the M center merely broadens this transmission around Γ, thereby boosting TMR to %315. Rotating a M center so as to partly point along the transmission direction sharpens transmission around Γ, further increasing TMR to 1423%. When these defects are placed at the MTJ interface, the transmission and ensuing TMR, which reaches ≈4000%, suggest that such junctions behave as would an ideal MTJ, only with a much lower barrier height. Our results thus theoretically reconcile the concurrent observations of high TMR and low barrier heights, in line with experimental preparation techniques such as post-deposition oxidation of metallic Mg, which can generate oxygen vacancies at the lower MTJ interface, and annealing which can promote M centers over F centers. Our theory is also in line with an origin of perpendicular magnetic anisotropy in terms of oxygen vacancies at MTJ interfaces. The effective size of these vacancies sets a limit for both the barrier thickness, in line with experiment, as well as for the MTJ's lateral dimension. Our work provides a much-needed theoretical basis to move beyond the mostly unsuspected, fortuitous defect engineering of spintronic performance that has thus far propelled MgO-based spintronics and its applications.

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Section: Rotating the M Centersupporting

confidence: 83%

“…This second point sheds precious light into how a MgO-class MTJ can experimentally exhibit both high TMR and a low barrier height. Indeed, the MgO barrier is often formed atop the FeCoB metallic surface by sputtering metallic Mg, followed by an oxidation step [67,68].…”

Section: Effect Of Shifting the Vacancy On The Transmissionmentioning

confidence: 99%

Impact of single and double oxygen vacancies on electronic transport in Fe/MgO/Fe magnetic tunnel junctions

Taudul,

Bowen,

Alouani

2019

Preprint

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“…So far, only introducing oxygen into the Ar sputter pressure alters this ratio, while postdeposition annealing does not . Here, we adopt another well‐established recipe of oxidizing a Mg layer, which alters the spintronic properties of the ensuing MTJs . Samples were postannealed to a temperature T a (see the Experimental Section).…”

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confidence: 99%

Tunneling Spintronics across MgO Driven by Double Oxygen Vacancies

Taudul

Monteblanco

Halisdemir

et al. 2017

Adv Elect Materials

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Δ 1 symmetry in the magnetic tunnel junction's (MTJ's) parallel orientation of electrode magnetization. Yet these high values of TMR are achieved across barriers with an energetic height as low as 0.4 eV. [7] This severe contradiction between experiment and theory, which enables spin-transfer torque (STT) experiments [2,8] thanks to a low resistance⋅area (RA) product, is suspected to reflect the impact on spintronics of structural defects in the MgO barrier [9] such as oxygen vacancies.The general consensus is that oxygen vacancies negatively impact tunneling spintronic performance, [10][11][12][13] leading to efforts to eliminate oxygen vacancies in MgO. [14] Recently, Schleicher et al. experimentally examined [15,16] how the ground and excited (denoted *) states of single oxygen vacancies, called F centers, decrease TMR. They also proposed, by cross-checking experimental [13,14] and theoretical [17,18] reports, that double oxygen vacancies, called M centers, might in fact enhance TMR. Yet a theory of spintronic tunneling mediated by M centers is lacking, as are magnetotransport experiments that explicitly identify this species within the MgO tunnel barrier. We confirm this counterintuitive yet very portent hypothetical proposal through ab initio calculations (performed within the generalized gradient approximation, or GGA; see the Experimental Section) and magnetotransport experiments, thereby bridging this knowledge gap.We present in Figure 1a the density of states (DOS) of bulk MgO without and with M centers (labeled M-MgO). The double oxygen vacancy results in the creation of two occupied energy levels below Fermi level (E F ), which we denote as the ground states M 1 and M 2 . Additionally, two new unoccupied energy states appear near the minimum of the conduction band, which we denote as the excited states M 1 * and M 2 *. Compared to the case of a F center, [10] the presence of pairs of ground and excited states reflects the bonding/antibonding interaction between the two F centers that form the M center (see insets to Figure 1a). Since the charge density onto the vacancy exhibits a mostly spherical distribution, we infer that the ground states of the M center are of s-like character. We note how the electron density plots also reveal a hybridization between the ground states and the first-nearest-neighbor oxygen ions. As we discuss Tunneling spintronic devices are foreseen to play an important role in emerging technologies, from data read-out and storage to processing, including neuromorphic computing. A counterintuitive suspicion is that double oxygen vacancies within the commonly used MgO barrier underscore the high spintronic performance. Here, how the peculiar electronic properties of these nanoscale objects experimentally enhance spintronic performance is demonstrated. The vacancy's ground state near the Fermi level theoretically promotes enhanced transmission across the barrier of electrons with the Δ 1 electronic symmetry that drives high spintronic performance. Annealing the MgO barrier experimen...

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Influence of seed layer on the magnetoresistance properties in IrMn-based magnetic tunnel junctions

Chen

Hao

et al. 2022

Journal of Magnetism and Magnetic Materials

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Effect of Seed Layer on Room Temperature Tunnel Magnetoresistance of MgO Barriers Formed by Radical Oxidation in IrMn-Based Magnetic Tunnel Junctions

Cited by 4 publications

References 31 publications

Impact of single and double oxygen vacancies on electronic transport in Fe/MgO/Fe magnetic tunnel junctions

Impact of single and double oxygen vacancies on electronic transport in Fe/MgO/Fe magnetic tunnel junctions

Tunneling Spintronics across MgO Driven by Double Oxygen Vacancies

Influence of seed layer on the magnetoresistance properties in IrMn-based magnetic tunnel junctions

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