Impact of electron-electron interactions induced by disorder at interfaces on spin-dependent tunneling in Co-Fe-B/MgO/Co-Fe-B magnetic tunnel junctions

Bernos, Julien; Hehn, M.; Montaigne, F.; Tiuşan, C.; Lacour, Daniel; Alnot, M.; Négulescu, B.; Lengaigne, G.; Snoeck, E.; Aliev, F. G.

doi:10.1103/physrevb.82.060405

Cited by 19 publications

(29 citation statements)

References 33 publications

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“…(ii) A second anomaly around ±350 mV was also observed [20,21,22,24,25,32] and related first to the electronic band structure of MgO [32] and later more specifically to certain features of the band structure of the ferromagnetic electrode [21][22][23][24][25]. A similar anomaly around ±200 mV observed in Fe/MgO/Fe MTJs has been explained with the role of the 5 majority band [23].…”

Section: Introductionmentioning

confidence: 65%

“…[22], the CoFe 5 and 2 bands are ruled out from causing the anomaly, other authors suggest the 5 majority or the 1 minority band to be the origin of this anomaly [21], or minority states with 5 symmetry [25]. This point will be discussed further below.…”

Section: Introductionmentioning

confidence: 86%

“…Furthermore, studying the effect of annealing on the I -V characteristics might help to discriminate between several conceivable mechanisms. Several groups [20][21][22] have reported modifications of the I -V characteristics by annealing at particular temperatures, but the gradual evolution with annealing time of I (V ) together with the TMR ratio for various temperatures has not been studied quantitatively so far. It is the aim of the present paper to investigate the time dependence of I (V ) during annealing at different temperatures and correlate it with the time evolution of the TMR ratio.…”

Section: Introductionmentioning

confidence: 99%

“…[21,24,26,30,32,33,36], is controversially interpreted either as signature of magnetic impurity scattering corresponding to the Kondo effect [32], in particular by magnetic impurity scattering in the MgO barrier [36], or as a consequence of electron-electron scattering at disordered interfaces [21], or due to magnon excitations [24,30,31].…”

Section: Introductionmentioning

confidence: 99%

“…[24] the effect of annealing on the anomalies was not explicitly investigated, a gradual decrease of the amplitude of the ZBA by a 1 hour anneal at increasing temperatures (200 • C, 250 • C, 300 • C) was found in Ref. [21], but the kinetics of the ZBA and the 350 mV anomaly during annealing were not investigated. It is the intention of the present paper to study the evolution in time of the I -V characteristics of CoFeB/MgO/CoFeB MTJs by annealing at different temperatures in order to identify a possible correlation between the crystallization and diffusion kinetics responsible for the increasing TMR ratio and the peculiar features of the I -V characteristics.…”

Section: Introductionmentioning

confidence: 99%

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Conductance anomalies of CoFeB/MgO/CoFeB magnetic tunnel junctions

et al. 2014

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The I -V characteristics of CoFeB/MgO/CoFeB magnetic tunnel junctions show pronounced nonlinearities which are relevant both for sensor applications and for the basic understanding of spin-dependent tunneling. To study the relation between the tunnel characteristics and the tunnel magnetoresistance (TMR) ratio, a series of CoFeB/MgO/CoFeB junctions was annealed with stepwise increasing annealing time at different temperatures. The related TMR ratio and the I -V characteristics were measured in the temperature range between 15 K and 300 K. This allowed the comparison of I -V characteristics of the same junction for TMR ratios between 25% and 150% at 300 K thus eliminating the influence of variations in the preparation process of separate individual samples. In addition to a zero bias anomaly observed in particular at low temperatures and for large TMR ratios, a conductance anomaly in the I -V curves was observed around a bias voltage of 350 mV. A general correlation between the deviation from Ohmic I -V characteristics and the TMR ratio was found both for parallel and antiparallel magnetizations of both ferromagnetic layers. This means that the shape of the I -V curves directly scales with the spin polarization of the tunneling current and the proportion of coherent electron tunneling. Both the 350 mV conductance anomaly and the correlation between non-Ohmic characteristics and the TMR ratio can be explained by considering the contributions of the relevant majority and minority spin bands of the ferromagnetic contacts.

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Section: Introductionmentioning

confidence: 65%

Section: Introductionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Conductance anomalies of CoFeB/MgO/CoFeB magnetic tunnel junctions

et al. 2014

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Probing a Device's Active Atoms

et al. 2017

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Materials science and device studies have, when implemented jointly as "operando" studies, better revealed the causal link between the properties of the device's materials and its operation, with applications ranging from gas sensing to information and energy technologies. Here, as a further step that maximizes this causal link, the paper focuses on the electronic properties of those atoms that drive a device's operation by using it to read out the materials property. It is demonstrated how this method can reveal insight into the operation of a macroscale, industrial-grade microelectronic device on the atomic level. A magnetic tunnel junction's (MTJ's) current, which involves charge transport across different atomic species and interfaces, is measured while these atoms absorb soft X-rays with synchrotron-grade brilliance. X-ray absorption is found to affect magnetotransport when the photon energy and linear polarization are tuned to excite FeO bonds parallel to the MTJ's interfaces. This explicit link between the device's spintronic performance and these FeO bonds, although predicted, challenges conventional wisdom on their detrimental spintronic impact. The technique opens interdisciplinary possibilities to directly probe the role of different atomic species on device operation, and shall considerably simplify the materials science iterations within device research.

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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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Impact of electron-electron interactions induced by disorder at interfaces on spin-dependent tunneling in Co-Fe-B/MgO/Co-Fe-B magnetic tunnel junctions

Cited by 19 publications

References 33 publications

Conductance anomalies of CoFeB/MgO/CoFeB magnetic tunnel junctions

Conductance anomalies of CoFeB/MgO/CoFeB magnetic tunnel junctions

Probing a Device's Active Atoms

Tunneling Spintronics across MgO Driven by Double Oxygen Vacancies

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