Polarity-tunable magnetic tunnel junctions based on ferromagnetism at oxide heterointerfaces

Ngo, Thach D. N.; Chang, Jung Won; Lee, Kyujoon; Han, Sangyong; Lee, Joon Sung; Kim, Young Heon; Jung, Myung Hun; Doh, Yong-Joo; Choi, Myeon-Song; Song, J. H.; Kim, Jinhee

doi:10.1038/ncomms9035

Cited by 27 publications

(25 citation statements)

References 45 publications

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“…Indeed, the presence or the lack of a spin-resolved charge could be then crucially related to the very specific characteristics of the considered sample. According to this interpretation, spin-polarized transport in LAO/STO would be a substantially fragile occurrence, thus accounting for the apparent contrast in the existing literature between cases of substantial [18][19][20] or marginal [22,23] presence of spin-polarization at the LAO/STO interface as transferred from FM electrodes.…”

Section: Discussionmentioning

confidence: 98%

“…However, there is no clear evidence, so far, that this route to 2DEG magnetization can work for LAO/STO as well. In literature only a couple of cases report electric spin transfer from on-top magnetic electrodes into LAO/STO [18,19]. In particular, reference [18] reports transfer from FM Co electrodes with surprisingly long in-plane spin diffusion length of d spin ∼1 μm in the 2DEG, as estimated by Hanle effect, which is much larger than the estimate derived from the analysis of weak localization magnetoresistance [4], but consistent with estimates extracted from spin Hall effect in a non-local geometry [5].…”

Section: Introductionmentioning

confidence: 99%

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Study of equilibrium carrier transfer in LaAlO₃/SrTiO₃ from an epitaxial La_1−xSr _xMnO₃ ferromagnetic layer

et al. 2018

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Using x-ray magnetic circular dichroism and ab-initio calculations, we explore the La 1−x Sr x MnO 3 /LaAlO 3 /SrTiO 3 (001) heterostructure as a mean to induce transfer of spin polarized carriers from ferromagnetic La 1−x Sr x MnO 3 layer into the 2DEG (two-dimensional electron gas) at the LaAlO 3 /SrTiO 3 interface. By out-of-plane transport measurements, the tunneling across the LaAlO 3 barrier is also analyzed. Our results suggest small or vanishing spin-polarization for the 2DEG: magnetic dichroism does not reveal a neat signal on Ti atoms, while calculations predict, for the pristine stoichiometric interface, a small spin-resolved mobile charge of 2.5×10 13 cm −2 corresponding to a magnetic moment of 0.038 μ B per Ti atom, tightly confined within the single SrTiO 3 layer adjacent to LaAlO 3 . Such a small magnetization is hard to be detected experimentally and perhaps not robust enough to survive to structural disorder, native doping, or La 1−x Sr x MnO 3 dead-layer effects. Our analysis suggests that, while some spin-diffusion cannot be completely ruled out, the use of ferromagnetic La 1−x Sr x MnO 3 epilayers grown on-top of LaAlO 3 /SrTiO 3 is not effective enough to induce robust spin-transport properties in the 2DEG. The examined heterostructure is nevertheless an excellent test-case to understand some fundamental aspects of the spin-polarized charge transfer in 2D wells.

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Section: Discussionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Study of equilibrium carrier transfer in LaAlO₃/SrTiO₃ from an epitaxial La_1−xSr _xMnO₃ ferromagnetic layer

et al. 2018

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“…Experimentally, U 2 corresponds to the backgate voltage and controls the carrier density on the QW (or the LAO/STO interface). In the recent experiment [11], on the other hand, the TMR did not depend much on the gate voltage. However, the actual gate capacitance was not known and it is not clear how large is the actual energy range covered by the gate voltage variation.…”

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confidence: 99%

“…Despite a number of experimental studies of the system, the origins of magnetic ordering and superconductivity remain controversial [17,18] and further studies are imperative. The sign-switching anisotropic TMR [11] adds a fresh intriguing question concerning the magnetic properties of the LAO/STO interface. Our results below suggest one possible explanation for it in terms of our MTJ model mentioned above.…”

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confidence: 99%

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Negative tunneling magneto-resistance in quantum wires with strong spin–orbit coupling

Han¹,

Serra²,

Choi³

2015

J. Phys.: Condens. Matter

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We consider a two-dimensional magnetic tunnel junction of the FM/I/QW(FM+SO)/I/N structure, where FM, I and QW(FM+SO) stand for a ferromagnet, an insulator and a quantum wire (QW) with both magnetic ordering and Rashba spin-orbit (SOC), respectively. The tunneling magneto-resistance (TMR) exhibits strong anisotropy and switches sign as the polarization direction varies relative to the QW axis, due to interplay among the one-dimensionality, the magnetic ordering, and the strong SOC of the QW. The results may provide a possible explanation for the sign-switching anisotropic TMR recently observed in the LaAlO3/SrTiO3 interface.The magnetic tunneling junction (MTJ) consisting of two ferromagnetic electrodes (FM) separated by a thin insulating barrier (I) is a prototype structure in the rapidly developing field of spintronics [1]. The tunneling magneto-resistance (TMR), depending on the relative magnetic polarization of the two FMs, is a key issue not only for the spintronic applications but also for the study of fundamental magnetic properties [2,3]. Due to the spin selection rule the TMR, if any, is typically positive. Two exceptional cases have been known. One involves magnetic impurities in the tunnel barriers and is not surprising. The other (more important) case is associated with the resonant tunneling and spin-dependent interfacial phase shift in double-barrier FM/I/N/I/FM structures, where N represents a non-magnetic normal metal [4][5][6][7][8].In this work we explore another non-trivial example of negative TMR in a two-dimensional (2D) doublebarrier MTJ of the FM/I/QW(FM+SO)/I/N structure [see Fig. 1 (a)], where QW(FM+SO) stands for a quantum wire (QW) with both magnetic ordering and Rashba spin-orbit coupling (SOC). Our MTJ structure should be distinguished from more common 1D MTJs of the FM/I/QW/I/FM structure such as in [5], where the QW is non-magnetic and the junction interface is perpendicular to the axis of the QW. In our case, the QW itself has a magnetic ordering and the junction interface is parallel to its axis. Thus, transport occurs across, not along the QW. We find that the TMR exhibits strong anisotropy and even changes sign as the polarization direction of the FMs varies relative to the QW axis. This sign-switching anisotropic TMR is attributed to the interplay among the one-dimensionality, the magnetic ordering, and the strong SOC of the QW. It is interesting to recall that anisotropic TMR was previously studied in the FM/I/FM structure where the insulating barrier (not the FMs) had SOC (see [10] and references therein), but the TMR remained positive without switching its sign.Our MTJ structure is peculiar in that nanoscale QWs with both strong SOC and magnetic ordering are rare. However, an important motivation is the recent experiment [11] on the transition metal oxide interface between LaAlO 3 (LAO) and SrTiO 3 (STO) [see Fig. 1 (b)], where the measured TMR is strongly anisotropic and switches sign as the magnetization direction varies in the interface plane. Since the LAO/STO interface...

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Interface Engineering and Emergent Phenomena in Oxide Heterostructures

et al. 2018

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Complex oxide interfaces have mesmerized the scientific community in the last decade due to the possibility of creating tunable novel multifunctionalities, which are possible owing to the strong interaction among charge, spin, orbital, and structural degrees of freedom. Artificial interfacial modifications, which include defects, formal polarization, structural symmetry breaking, and interlayer interaction, have led to novel properties in various complex oxide heterostructures. These emergent phenomena not only serve as a platform for investigating strong electronic correlations in low-dimensional systems but also provide potentials for exploring next-generation electronic devices with high functionality. Herein, some recently developed strategies in engineering functional oxide interfaces and their emergent properties are reviewed.

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Polarity-tunable magnetic tunnel junctions based on ferromagnetism at oxide heterointerfaces

Cited by 27 publications

References 45 publications

Study of equilibrium carrier transfer in LaAlO₃/SrTiO₃ from an epitaxial La_1−xSr _xMnO₃ ferromagnetic layer

Study of equilibrium carrier transfer in LaAlO₃/SrTiO₃ from an epitaxial La_1−xSr _xMnO₃ ferromagnetic layer

Negative tunneling magneto-resistance in quantum wires with strong spin–orbit coupling

Interface Engineering and Emergent Phenomena in Oxide Heterostructures

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Polarity-tunable magnetic tunnel junctions based on ferromagnetism at oxide heterointerfaces

Cited by 27 publications

References 45 publications

Study of equilibrium carrier transfer in LaAlO3/SrTiO3 from an epitaxial La1−x Sr x MnO3 ferromagnetic layer

Study of equilibrium carrier transfer in LaAlO3/SrTiO3 from an epitaxial La1−x Sr x MnO3 ferromagnetic layer

Negative tunneling magneto-resistance in quantum wires with strong spin–orbit coupling

Interface Engineering and Emergent Phenomena in Oxide Heterostructures

Contact Info

Product

Resources

About

Study of equilibrium carrier transfer in LaAlO₃/SrTiO₃ from an epitaxial La_1−xSr _xMnO₃ ferromagnetic layer

Study of equilibrium carrier transfer in LaAlO₃/SrTiO₃ from an epitaxial La_1−xSr _xMnO₃ ferromagnetic layer