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9 Feb 2004

Volume 84, Issue 6, pp. 837-1024

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Appl. Phys. Lett. 84, 975 (2004); http://dx.doi.org/10.1063/1.1646453 (3 pages)

Xiang Yang Kong and Zhong Lin Wang
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Direct observation of magnetic depth profiles of thin Fe films on Cu(100) and Ni/Cu(100) with the depth-resolved x-ray magnetic circular dichroism

K. Amemiya, S. Kitagawa, D. Matsumura, H. Abe, T. Ohta, and T. Yokoyama

Appl. Phys. Lett. 84, 936 (2004); http://dx.doi.org/10.1063/1.1645330 (3 pages) | Cited 22 times

Online Publication Date: 4 February 2004

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A depth-resolved technique in the x-ray magnetic circular dichroism (XMCD) has been developed and applied to Fe/Cu(100) and Fe/Ni/Cu(100) in order to observe the magnetic depth profile directly. It was confirmed that the surface two layers of the 7 ML Fe/Cu(100) are ferromagnetically coupled, while the inner layers are in the spin density wave (SDW) state at 130 K. The technique enables one to extract the XMCD spectra from the surface ferromagnetic (FM) and inner SDW regions separately, indicating that the FM/SDW interface has an antiparallel magnetic coupling, and that the SDW region has the bulk-like feature. For Fe/Ni/Cu(100), we have observed magnetically live surface layers and some thickness dependent magnetic coupling between the Fe surface and Ni film. © 2004 American Institute of Physics.
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75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.55.-a Thin film structure and morphology
75.30.Ds Spin waves
78.20.Fm Birefringence
78.20.Ls Magneto-optical effects
78.66.Bz Metals and metallic alloys
78.70.Dm X-ray absorption spectra

Control of magnetization states in microstructured permalloy rings

Marcus Steiner and Junsaku Nitta

Appl. Phys. Lett. 84, 939 (2004); http://dx.doi.org/10.1063/1.1646223 (3 pages) | Cited 41 times

Online Publication Date: 4 February 2004

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Magnetization processes of microstructured NiFe rings are studied by the fringe-field-induced local Hall effect and numerical model calculations. The changes in reversible and irreversible magnetization of single rings are detected with very high resolution. We observe that the type of magnetic transition depends on the ratio between the inner and outer ring diameter. For narrow rings, sharp transitions from so-called “onion” to the “vortex” state are observed. In rings with smaller inner diameter, the transitions are more complex. The creation of local vortices and their spatial movement by applying an external magnetic field are detected. © 2004 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.40.Mg Numerical simulation studies

Correlations between pressure and bandwidth effects in metal–insulator transitions in manganites

Congwu Cui and Trevor A. Tyson

Appl. Phys. Lett. 84, 942 (2004); http://dx.doi.org/10.1063/1.1646212 (3 pages) | Cited 11 times

Online Publication Date: 4 February 2004

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The effect of pressure on the metal–insulator transition in manganites with a broad range of bandwidths is investigated. A critical pressure is found at which the metal–insulator transition temperature, TMI, reaches a maximum value in every sample studied. The origin of this universal pressure and the relation between the pressure effect and the bandwidth on the metal–insulator transition are discussed. © 2004 American Institute of Physics.
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71.30.+h Metal-insulator transitions and other electronic transitions
75.50.Dd Nonmetallic ferromagnetic materials
62.50.-p High-pressure effects in solids and liquids

Low-current blocking temperature writing of double barrier magnetic random access memory cells

Jianguo Wang and P. P. Freitas

Appl. Phys. Lett. 84, 945 (2004); http://dx.doi.org/10.1063/1.1646211 (3 pages) | Cited 17 times

Online Publication Date: 4 February 2004

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A magnetic random access memory cell architecture is fabricated where the pinned layer is reversed by heating above a reduced blocking temperature with a current pulse crossing the junction, and cooled under an external applied field (word line), minimizing half-select switching of nonaddressed bits. In order to improve Joule heating and increase breakdown voltage, a double barrier structure was used, with a common antiferromagnetic layer (60 Å MnIr) two pinned 30 Å CoFe layers, and two free layers incorporating nanooxide structures. The blocking temperature was reduced to 120 °C. A TMR of 25% was achieved for both single barrier and double barrier tunnel junctions with resistance×area products of ∼ 40 Ω×μm2 and ∼ 280 Ω×μm2, respectively. Pinned layer writing allows the definition of a three-state memory, requiring, however, a destructive read out. A significant improvement of writing efficiency is observed with the double barrier structure. A 10 ns current pulse of 9 mA/μm2 is sufficient to heat the double barrier junctions above the blocking temperature and induce pinned layer switching. © 2004 American Institute of Physics.
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75.50.Ee Antiferromagnetics
84.30.Sk Pulse and digital circuits
85.75.Dd Magnetic memory using magnetic tunnel junctions

Thickness dependent magnetization states of Fe islands on W(110): From single domain to vortex and diamond patterns

M. Bode, A. Wachowiak, J. Wiebe, A. Kubetzka, M. Morgenstern, and R. Wiesendanger

Appl. Phys. Lett. 84, 948 (2004); http://dx.doi.org/10.1063/1.1644613 (3 pages) | Cited 13 times

Online Publication Date: 4 February 2004

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We have studied the thickness dependent domain configuration of single-crystal nanoscale Fe islands on W(110) by spin-polarized scanning tunneling microscopy. The experimental results are compared with micromagnetic calculations. For very thin islands, the uniaxial surface anisotropy of Fe/W(110) leads to a single domain state. With increasing island thickness, the magnetostatic energy becomes increasingly important resulting in different flux closure configurations. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
75.70.Kw Domain structure (including magnetic bubbles and vortices)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
75.70.Rf Surface magnetism
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.30.Gw Magnetic anisotropy

Switching processes and switching reproducibility in ferromagnetic ring structures

M. Kläui, C. A. F. Vaz, J. A. C. Bland, E. H. C. P. Sinnecker, A. P. Guimarães, W. Wernsdorfer, G. Faini, E. Cambril, L. J. Heyderman, and C. David

Appl. Phys. Lett. 84, 951 (2004); http://dx.doi.org/10.1063/1.1640451 (3 pages) | Cited 35 times

Online Publication Date: 4 February 2004

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We present an experimental study of the reproducibility of the different switching processes occurring in rings. Using superconducting quantum interference device and magnetoresistance measurements, we can measure hysteresis loops of arrays of rings and single structures at varying temperatures and thereby separate the influence of thermal excitations and defects (extrinsic and intrinsic). We find that the temperature dependence of the switching fields and their distributions can be correlated with the different physical processes occurring during different transitions. Measurements of the angular dependence of the switching fields of a single ring allow us to distinguish the contributions of extrinsic and intrinsic defects to the switching field distributions and, counterintuitively, it is established that transitions involving nucleation processes are less prone to defects and thermal excitations than processes involving domain-wall or vortex core depinning and propagation. © 2004 American Institute of Physics.
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85.70.-w Magnetic devices
85.25.Dq Superconducting quantum interference devices (SQUIDs)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys
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