Electrical switching in Fe∕Cr∕MgO∕Fe magnetic tunnel junctions

Abstract

Hysteretic resistance switching is observed in epitaxial Fe∕Cr∕MgO∕Fe magnetic tunnel junctions under bias voltage cycling between negative and positive values of about 1V. The junctions switch back and forth between high- and low-resistance states, both of which depend on the device bias history. A linear dependence is found between the magnitude of the tunnel magnetoresistance and the crafted resistance of the junctions. To explain these results, a model is proposed that considers electron transport both by elastic tunneling and by defect-assisted transmission.

Localized states in advanced dielectrics from the vantage of spin- and symmetry-polarized tunnelling across MgO

“…Stacks were post-annealed in an in-plane magnetic field of 200 Oe for 1 h at 300°C to both crystallize the MgO barrier and pin the lower electrode, thanks to the IrMn antiferromagnetic layer. Samples were then processed within the STNano technological platform by optical lithography into arrays of junctions with sizes varying between 14 and 40 mm in diameter 8 . Typical resistance-area values are 6 Â 10 7 O mm 2 (see Supplementary Note 3 for a RA map).…”

“…This impedes an assessment of the impact that such defects may have on the nominally expected materials property. For instance, magnetic tunnel junctions (MTJs) that comprise a ferroelectric 3 or multiferroic 4 barrier yield devices with four addressable states, yet the same result may be achieved with a simple paraelectric barrier with altered stoichiometry [5][6][7][8] . Furthermore, at the nanoscale, defects shall strongly affect a dielectric material's effective properties, including the intrinsic property that prompted initial research interest in the material.…”

“…Spin-polarized solid-state tunnelling spectroscopy on lithographically processed stacks 8 can reveal the junction electrodes' electronic structure 12,55 , the junction's symmetry-resolved barrier heights 37 and inelastic tunnelling phenomena 19 that includes hopping onto defect states 24 . We note that, since the D 1 complex loop, which spans the band gap and defines the wavefunction decay through tunnelling, is rather flat within at least ± 1.1 eV about the band gap centre, both electron and hole tunnelling with respect to states above and below E F are considered 37 (rescaling the local density approximation (LDA)-derived 4.7 eV MgO band gap to its experimental value of 7.8 eV yields a flat D 1 band over 2.2 eV about the charge-neutrality level-pegged chemical potential 37 .…”

Resistance switching in transparent magnetic MgO films

“…On the one hand, MgO addition to ZnO layers (Mgx Zn 1−x O) has shown to improve data retention characteristics in non-volatile memory architectures [10]. Moreover, electrical switching that has been observed in MgO films [13] and MgO-based magnetic tunnel junctions [14][15][16] is attributed either to nanostructural rearrangements of metallic ions in the electrode/barrier interfaces or reversible displacement of oxygen vacancies. On the other hand, defect-induced ferromagnetism in MgO has already been observed at room temperature [17][18][19][20][21].…”

Voltage-controlled inversion of tunnel magnetoresistance in epitaxial nickel/graphene/MgO/cobalt junctions

“…To ensure low roughness and strong sticking of the oxide layer on graphene, 0.12 nm of Ti were dusted on the substrate prior to MgO deposition [18]. During MgO evaporation, the latter decomposes into atomic Mg and O species [19], resulting in a ~5.10 -8 torr oxygenated atmosphere that oxidizes Ti into TiO 2 [17,20]. This small amount of titanium oxide improves the uniformity of the MgO layer [18].…”