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21 Feb 2000

Volume 76, Issue 8, pp. 943-1075

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Strongly reduced bias dependence in spin–tunnel junctions obtained by ultraviolet light assisted oxidation

H. Boeve, E. Girgis, J. Schelten, J. De Boeck, and G. Borghs

Appl. Phys. Lett. 76, 1048 (2000); http://dx.doi.org/10.1063/1.125934 (3 pages) | Cited 24 times

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For future implementation of ferromagnetic tunnel junctions, we need a better understanding of the influence of the insulating barrier preparation method on the junction resistance, tunnel magnetoresistance (TMR), and its voltage bias dependence. In this letter, we focus on the bias dependence of junctions (Co–Al2O3–Ni80Fe20) prepared by ultraviolet light assisted in situ oxidation in an O2 ambient. For an initial Al thickness of 1.3 nm, the resistance times area product of the junctions is 60 kΩ μm2, while showing up to 20% TMR at 5 mV bias. The decrease of TMR with bias voltage up to 1 V is remarkably small leading to V1/2, for which half of the low-bias TMR remains, well over 0.6 V. © 2000 American Institute of Physics.
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73.40.Rw Metal-insulator-metal structures
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.65.Mq Oxidation
81.05.Bx Metals, semimetals, and alloys
75.50.Bb Fe and its alloys
75.47.De Giant magnetoresistance
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys
82.50.-m Photochemistry
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Oxygen-deficiency-activated charge ordering in La2/3Sr1/3MnO3−δ thin films

J. Li, C. K. Ong, J.-M. Liu, Q. Huang, and S. J. Wang

Appl. Phys. Lett. 76, 1051 (2000); http://dx.doi.org/10.1063/1.125935 (3 pages) | Cited 34 times

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The oxygen-deficiency-activated charge ordering (CO) transition has been observed in C-oriented La2/3Sr1/3MnO3−δ thin films prepared by pulsed laser deposition on LaAlO3 substrates. A rapid growth of the sample resistivity at temperatures below TC is observed, while significant thermal hysteresis and electrical field induced transition from the insulator CO state to metallic-like state are recorded. Such a CO state can also be partially melted under a magnetic field of 0.4 T, resulting in enhanced magnetoresistance at low temperatures. Magnetic properties of the films can be well understood as the coexistence of the ferromagnetic state and the CO state. The CO state in oxygen deficient thin films is explained in terms of the Mn–O octahedral distortion or the narrowness of the conduction bandwidth of the eg carriers. © 2000 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.47.Gk Colossal magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
71.30.+h Metal-insulator transitions and other electronic transitions
81.15.Fg Pulsed laser ablation deposition
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Melt-spun precipitation-hardened Sm2(Co, Cu, Fe, Zr)17 magnets with abnormal temperature dependence of coercivity

D. Goll, I. Kleinschroth, W. Sigle, and H. Kronmüller

Appl. Phys. Lett. 76, 1054 (2000); http://dx.doi.org/10.1063/1.125936 (3 pages) | Cited 39 times

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Rapidly quenched Sm(CobalCu0.08Fe0.22Zr0.02)8.5 (Cu-/Fe-rich) and Sm(CobalCu0.05Fe0.10Zr0.03)8.5 (Cu-/Fe-poor) ribbons have been prepared by means of the melt-spinning technique. By applying an appropriate annealing procedure a microstructure similar to that of sintered magnets can be obtained. The energy dispersive x-ray microanalysis of the compositional dependence near the cell boundaries suggests a model for the profile of the crystal anisotropy constants responsible for the magnetic hardening. The Cu-/Fe-rich alloy shows a normal temperature dependence of coercivity with a negative temperature coefficient, but the Cu-/Fe-poor ribbons show a positive temperature coefficient in the temperature range from 400–700 K. The different temperature coefficients are discussed in terms of a pinning model. © 2000 American Institute of Physics.
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75.50.Ww Permanent magnets
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
81.05.Bx Metals, semimetals, and alloys
75.50.Vv High coercivity materials
61.72.Cc Kinetics of defect formation and annealing
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.30.Bx Phase diagrams of metals, alloys, and oxides

Suppression of exchange bias by ion irradiation

T. Mewes, R. Lopusnik, J. Fassbender, B. Hillebrands, M. Jung, D. Engel, A. Ehresmann, and H. Schmoranzer

Appl. Phys. Lett. 76, 1057 (2000); http://dx.doi.org/10.1063/1.125937 (3 pages) | Cited 57 times

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The exchange bias effect in ferromagnetic/antiferromagnetic sandwich structures is generally believed to be sensitive on the interface exchange interaction, the magnetization, and the thickness of the ferromagnetic layer. Also the interface structure plays a crucial role. We show that, by irradiating samples with He ions, we can manipulate the exchange bias field in a controlled manner. Depending on the dose (1014–1017 ions/cm2) and the acceleration voltage (10–35 kV) of the ions, the shift of the hysteresis can be reduced or even fully suppressed. Potential applications of this effect for magnetic patterning on the nanoscale will be discussed. © 2000 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.35.Ct Interface structure and roughness
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
61.80.Jh Ion radiation effects
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