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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Kinetics of pinhole nucleation and growth in magnetic tunnel junctions

Changhe Shang, Yingjian Chen, and Ki-seok Moon

J. Appl. Phys. 93, 7017 (2003); http://dx.doi.org/10.1063/1.1555291 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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Tunnel junctions with different pinhole probabilities were obtained by varying natural oxidation condition. In pinhole-free junctions, the observed abrupt changes in magnetoresistance and junction resistance with increasing bias current are the signature of dielectric breakdown, and are attributed to the process of pinhole nucleation. On the contrary, low RA junctions show gradual changes in magnetoresistance and junction resistance with voltage, indicating the absence of pinhole nucleation, but only the process of pinhole growth starting from the inherent pinholes. Experimentally, the activation energy of pinhole growth (EG∼0.3 eV) is found to be much lower than that of pinhole nucleation (EN∼0.6eV), which explains the easy breakdown behavior observed in low RA junctions. © 2003 American Institute of Physics.
Show PACS
75.47.Np Metals and alloys
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.47.De Giant magnetoresistance

Noise properties of magnetic and nonmagnetic tunnel junctions

Wan Kyu Park, Jagadeesh S. Moodera, John Taylor, Mark Tondra, James M. Daughton, Andy Thomas, and Hubert Brückl

J. Appl. Phys. 93, 7020 (2003); http://dx.doi.org/10.1063/1.1558655 (3 pages) | Cited 11 times

Online Publication Date: 9 May 2003

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Low-frequency voltage fluctuations in magnetic and nonmagnetic tunnel junctions have been investigated. Tunneling magnetoresistance ratio of junctions ranged from 8.6% to 50% at room temperature. The origin of voltage noise was observed to be nonmagnetic. It was found that the resistance fluctuations lead to 1/f noise at room temperature, whereas the white noise was dominant at 77 K. A phenomenological noise parameter, defined for the comparison of noise levels in different junctions, was shown to scale with the junction resistance–area product. This observation suggests that low values of resistance×area are required for a low noise operation as well as for the integration of magnetic tunnel junctions. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
73.50.Td Noise processes and phenomena
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Interface characterization of magnetic tunnel junctions by using tunneling spectroscopy

Y. Ando, M. Hayashi, M. Oogane, H. Kubota, and T. Miyazaki

J. Appl. Phys. 93, 7023 (2003); http://dx.doi.org/10.1063/1.1540172 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2003

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Junctions doped with a small mount of Al between the top ferromagnetic electrode and the insulator were fabricated. The tunnel magnetoresistance (TMR) ratio increased at the doped Al thickness of 0.2 nm after annealing at 250 °C. Inelastic-electron-tunneling spectroscopy (IETS) has been applied to investigate the spin-dependent tunneling process for the tunnel junctions. The IET spectrum subtracting the spectrum at parallel magnetization configuration from that at antiparallel configuration showed a peak around 20 mV of the bias voltage especially for the junction after annealing at 250 °C. Over the corresponding voltage the TMR ratio as a function of the bias decreased; however, the influence was relatively small. © 2003 American Institute of Physics.
Show PACS
75.47.Np Metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.Mk Spin transport through interfaces
85.75.Dd Magnetic memory using magnetic tunnel junctions
75.30.Ds Spin waves
68.35.Ja Surface and interface dynamics and vibrations

Effect of nitrogen plasma treatment at the Al2O3/Fe interface in magnetic tunnel junction

Heejae Shim, B. K. Cho, Jin-Tae Kim, T. W. Kim, and W. J. Park

J. Appl. Phys. 93, 7026 (2003); http://dx.doi.org/10.1063/1.1540173 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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We investigated the effects of nitrogen plasma treatment on top surface of Fe pinned layer for short times (tex=0, 10, 30, and 60 s) in magnetic tunnel junctions and annealing of the junctions. The nitrogen-treated junctions show much reduced magnetoresistance (MR) ratio and significantly lower resistance-area (RA) products compared with the untreated junction, i.e., MR≈3%, RA≈30 kΩ μm2 for tex=10 s and MR≈10%, RA≈60 kΩ μm2 for tex=0 s. The untreated junction showed enhanced MR ratio up to about 17% and higher RA (≈70 kΩ μm2) upon thermal annealing at Ta=230 °C, as expected. For the nitrogen-treated junctions, while the MR ratio also increases up to about 16% upon annealing at Ta=230 °C, which is almost the same value as the one of the optimal reference junction, the RA values of the annealed junctions still keep as low as their initial values. We believe that the redistribution of nitrogen during the annealing process is responsible for the change of properties of nitrogen-treated junction. The bias dependence of MR and the estimation of effective barrier height and thickness are studied and found to be consistent with the observed changes in nitrogen-treated junctions. © 2003 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.75.Dd Magnetic memory using magnetic tunnel junctions
75.47.Np Metals and alloys
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.40.Gh Other heat and thermomechanical treatments
81.65.-b Surface treatments
52.77.-j Plasma applications

Resonant tunneling in magnetoresistive Ni/NiO/Co nanowire junctions

A. Sokolov, I. F. Sabirianov, E. Y. Tsymbal, B. Doudin, X. Z. Li, and J. Redepenning

J. Appl. Phys. 93, 7029 (2003); http://dx.doi.org/10.1063/1.1558657 (3 pages) | Cited 7 times

Online Publication Date: 9 May 2003

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Magnetotransport studies performed on electrodeposited Ni/NiO/Co nanojunctions show a broad distribution of magnetoresistance values spanning from +40% to −25%, with an average of about 2%, corresponding to observations on large-area junctions. The dispersion in the results can be understood in terms of tunneling via localized states in the barrier. Calculations based on Landauer–Büttiker theory explain this behavior in terms of disorder-driven statistical variations in magnetoresistance with a finite probability of the inversion of tunnel magnetoresistance sign due to resonant tunneling. © 2003 American Institute of Physics.
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75.75.-c Magnetic properties of nanostructures
73.63.Rt Nanoscale contacts
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Np Metals and alloys
73.23.Hk Coulomb blockade; single-electron tunneling
75.45.+j Macroscopic quantum phenomena in magnetic systems
75.50.Cc Other ferromagnetic metals and alloys
72.15.Rn Localization effects (Anderson or weak localization)
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