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Endurance of MgO-based magnetic tunnel junctions has been studied using a time-dependent dielectric breakdown method. Series of successive electrical pulses were applied until electrical breakdown of the tunnel barrier. We show that two electrical breakdown regimes exist depending on the time interval Δt between pulses compared to a characteristic escape time of trapped electrons τ0 ∼ 100 ns. For Δt < τ0, breakdown is caused by a high average charge trapped in the barrier. For Δt > τ0, breakdown is ascribed to large temporal modulation of trapped charges causing alternating stress in the barrier oxide. Between these two regimes, the tunnel junctions reach a very high endurance. [ABSTRACT FROM AUTHOR]

First-principles calculations of the electronic structures of chalcogenide spinels with anion vacancy and substitutions are presented. Our calculations predict that Cu(Cd)Cr2S(Se)4-x, CuCr2S(Se)4-xEx (E=F, Cl, Br), and CdCr2S(Se)4-xDx (D=N, P, As) can be half-metallic over a range of concentrations. The magnetic moment is found to scale approximately linearly on adding or withdrawing electrons and varies between 5.0 and 6.0 μB/f.u. [ABSTRACT FROM AUTHOR]

The so-called zigzag edge of graphenes theoretically has localized electrons due to the presence of flat energy bands near the Fermi level. The localized electron spins are strongly polarized, resulting in ferromagnetism. We fabricate graphenes with honeycomb-like arrays of hydrogen-terminated and low-defect hexagonal nanopores by a nonlithographic method using nanoporous alumina templates. We report large-magnitude room-temperature ferromagnetism caused by electron spins localizing at the zigzag nanopore edges. This promises to be a realization of rare-element free, controllable, transparent, flexible, and mono-atomic layer magnets and novel spintronic devices. [ABSTRACT FROM AUTHOR]