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8 Jan 2001

Volume 78, Issue 2, pp. 139-257

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Thermal stability of magnetic tunnel junctions studied by x-ray photoelectron spectroscopy

David J. Keavney, Sungkyun Park, Charles M. Falco, and J. M. Slaughter

Appl. Phys. Lett. 78, 234 (2001); http://dx.doi.org/10.1063/1.1338957 (3 pages) | Cited 17 times

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We have studied the evolution of chemical state of the metallic layers in NiFe/Al oxide/NiFe tunnel junction structures in as-deposited films and after postdeposition annealing. Both top and bottom NiFe layers in as-deposited films show significant Fe oxidation, but no Ni oxidation. This Fe is reduced in annealed samples, implying that oxygen migrates from the FeNi layers, possibly into the Al oxide layer. We also find that both top and bottom electrodes are significantly oxidized even in optimally annealed films. © 2001 American Institute of Physics.
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75.75.-c Magnetic properties of nanostructures
68.60.Dv Thermal stability; thermal effects
79.60.Jv Interfaces; heterostructures; nanostructures
72.25.Mk Spin transport through interfaces
75.45.+j Macroscopic quantum phenomena in magnetic systems
85.75.Mm Spin polarized resonant tunnel junctions
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
81.65.Mq Oxidation

Dispersion of the pinning field direction of a ferromagnet/antiferromagnet coupled system

Chunhong Hou, Jian Chen, Mark T. Kief, Zheng Gao, Sining Mao, and Taras Pokhil

Appl. Phys. Lett. 78, 237 (2001); http://dx.doi.org/10.1063/1.1335842 (3 pages) | Cited 10 times

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The exchange bias field of a ferromagnet/antiferromagnet bilayer is usually measured by the unidirectional shift of the hysteresis loop of the ferromagnetic layer. The exchange bias field results from interfacial exchange coupling between the spins in the ferromagnetic and antiferromagnetic layers. In general, the spins of the antiferromagnetic layer can vary locally in their anisotropy directions resulting in a distribution in local pinning directions. This letter reports a quantitative study on this distribution or dispersion using the anisotropic magnetoresistive (AMR) effect in a small rotating magnetic field. The AMR data as a function of the rotating angle of the field measured at a low field reveal the dispersion inside the ferromagnetic layer and at the interface of a ferromagnet/antiferromagnet system. The interaction between the domains within the ferromagnetic layer also plays a significant role in the dispersion inside the ferromagnetic layer. © 2001 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Et Exchange and superexchange interactions

Epitaxial-strain-induced insulator-superconductor transition in undoped and lightly doped La2CuO4

Weidong Si and X. X. Xi

Appl. Phys. Lett. 78, 240 (2001); http://dx.doi.org/10.1063/1.1338966 (3 pages) | Cited 14 times

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We have studied the epitaxial-strain effects on transport properties of pulsed-laser-deposited undoped and lightly doped La2CuO4 thin films. The epitaxial strain is controlled by using SrLaAlO4 buffer layers of different thicknesses on SrTiO3 substrates. The La2CuO4 films are insulating under tensile epitaxial strain, but when the strain is sufficiently compressive they become superconducting. Since the undoped and lightly doped La2CuO4 are known to be superconducting when interstitial oxygen is inserted, the epitaxial-strain-induced insulator–superconductor transition suggests a significant interplay between strain and oxygenation in the films. © 2001 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Magnetotransport and magnetic properties of La0.7MnO3−δ and Pr0.65Ba0.05Ca0.3MnO3−δ superlattices

Srinivas V. Pietambaram, D. Kumar, Rajiv K. Singh, and Clinton B. Lee

Appl. Phys. Lett. 78, 243 (2001); http://dx.doi.org/10.1063/1.1338498 (3 pages) | Cited 4 times

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Superlattice structures consisting of La0.7MnO3−δ (LMO) and Pr0.65Ba0.05Ca0.3MnO3−δ (PBCMO) systems, in which the thickness of La0.7MnO3−δ is fixed and that of Pr0.65Ba0.05Ca0.3MnO3−δ varied from 1 to 8 unit cells, have been grown in situ on (100) LaAlO3 substrates using a pulsed-laser deposition technique. Microstructural characterization carried out on these films shows the presence of characteristic intense satellite peaks, indicating the chemical modulation of the superlattice structure. The insulator-to-metal transition and the magnetoresistance (MR) ratio are found to vary with the number of unit cells. The samples with 1, 2, 5, and 8 unit cells of Pr0.65Ba0.05Ca0.3MnO3−δ show transition temperatures of 240, 230, 150, and 160 K and MR ratios of 540%, 592%, 3150%, and 2875%, respectively. We have observed an enhancement of magnetoresistance ratios in the case of superlattices with a thickness of PBCMO greater than 5 unit cells, which may be attributed to a ferromagnetic biasing provided by the LMO layers acting as a ferromagnetic film below its transition temperature. © 2001 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.75.-c Magnetic properties of nanostructures
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.65.Cd Superlattices
75.50.Dd Nonmetallic ferromagnetic materials
72.60.+g Mixed conductivity and conductivity transitions
81.15.Fg Pulsed laser ablation deposition

Rotational giant magnetoimpedance in soft magnetic wires: Modelization through Fourier harmonic contribution

C. Gómez-Polo, M. Vázquez, and M. Knobel

Appl. Phys. Lett. 78, 246 (2001); http://dx.doi.org/10.1063/1.1336814 (3 pages) | Cited 21 times

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A method to investigate the giant magnetoimpedance effect based on Fourier analysis is introduced. The study is carried out on a FeCoSiB amorphous wire with vanishing magnetostriction subjected to joule heating (current annealing) treatment that induces an enhancement of circumferential magnetic anisotropy and modifies the magnetoimpedance response of the samples. Experimental results are interpreted within the framework of the classical electrodynamical model, where the circumferential permeability plays the dominant role in the field dependence of the complex impedance of the sample. A rotational magnetization model is employed to determine the circular magnetization process, and a mean value of the circumferential permeability is obtained through the harmonic components obtained through Fourier analysis of the time derivative of the circular magnetization. This simple model is able to reproduce the observed experimental behavior, i.e., evolution of the field dependence of the complex impedance with annealing and the asymmetrical field dependence under a dc biased electrical current. © 2001 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.30.Gw Magnetic anisotropy
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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