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6 Dec 2004

Volume 85, Issue 23, pp. 5499-5791

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Appl. Phys. Lett. 85, 5694 (2004); http://dx.doi.org/10.1063/1.1828575 (3 pages)

M. Y. Shen, C. H. Crouch, J. E. Carey, and E. Mazur
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Low-current spin-transfer switching and its thermal durability in a low-saturation-magnetization nanomagnet

K. Yagami, A. A. Tulapurkar, A. Fukushima, and Y. Suzuki

Appl. Phys. Lett. 85, 5634 (2004); http://dx.doi.org/10.1063/1.1829140 (3 pages) | Cited 74 times

Online Publication Date: 8 December 2004

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A spin-transfer magnetization switching technique is a promising candidate as a writing mechanism for a high-density magnetic random access memory because of its scalability. The required switching current Ic, however, is still too large for this technique to be applied to MRAM using tunneling magnetoresistive devices. Here, it is demonstrated that reducing the saturation magnetization Ms of magnet cells is an effective way to decrease Ic. Use of a CoFeB film with μ0Ms of 0.75 T as a magnet cell reduced Ic measured with a continuous current by an order of magnitude. We changed the duration of a writing current pulse from 1 μs to 5 s to investigate thermal effects on the switching process, and predicted that CoFeB magnet cells with low Ic can be compatible with the thermal durability required for MRAM applications.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Sg Magnetocaloric effect, magnetic cooling
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.47.De Giant magnetoresistance

Head-to-head domain-wall phase diagram in mesoscopic ring magnets

M. Kläui, C. A. F. Vaz, J. A. C. Bland, L. J. Heyderman, F. Nolting, A. Pavlovska, E. Bauer, S. Cherifi, S. Heun, and A. Locatelli

Appl. Phys. Lett. 85, 5637 (2004); http://dx.doi.org/10.1063/1.1829800 (3 pages) | Cited 60 times

Online Publication Date: 8 December 2004

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The nanoscale spin structure of head-to-head domain walls in mesoscopic ferromagnetic rings has been studied by high-resolution nonintrusive photoemission electron microscopy as a function of both ring width (100–730 nm) and film thickness (2–38 nm). Depending on the geometry, two types of head-to-head domain walls are found (vortex and transverse walls). The experimental phase diagram, which identifies the transition between the wall types, is compared to analytical calculations of the energy and micromagnetic simulations, which are found to agree well with the experimental results.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
75.60.Ch Domain walls and domain structure
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
79.60.-i Photoemission and photoelectron spectra

Thin films of SmCo5 with very high perpendicular magnetic anisotropy

J. Sayama, K. Mizutani, T. Asahi, and T. Osaka

Appl. Phys. Lett. 85, 5640 (2004); http://dx.doi.org/10.1063/1.1829792 (3 pages) | Cited 27 times

Online Publication Date: 8 December 2004

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Thin films of SmCo5 with extraordinarily high perpendicular magnetic anisotropy were prepared by introducing a Cu∕Ti dual underlayer and controlling the substrate temperature during the sputter deposition. Under optimized conditions, the magnetic anisotropy constant reached 4.0×107 erg∕cm3, and the coercivity and the remanence ratio in the direction perpendicular to the film surface were 12.0 kOe and unity, respectively. The high perpendicular magnetic anisotropy is attributed to the high degree of preferred orientation of the c axis; the full width at half maximum in the rocking curve of SmCo5(002) reflection was 3.1°.
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81.05.Bx Metals, semimetals, and alloys
75.50.Cc Other ferromagnetic metals and alloys
75.30.Gw Magnetic anisotropy
75.50.Vv High coercivity materials
75.70.Ak Magnetic properties of monolayers and thin films
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Cd Deposition by sputtering

Magnetic-field-controllable avalanche breakdown and giant magnetoresistive effects in Gold∕semi-insulating-GaAs Schottky diode

Z. G. Sun, M. Mizuguchi, T. Manago, and H. Akinaga

Appl. Phys. Lett. 85, 5643 (2004); http://dx.doi.org/10.1063/1.1834733 (3 pages) | Cited 24 times

Online Publication Date: 8 December 2004

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Gold (Au)∕semi-insulating (SI)-GaAs Schottky diode was fabricated by the standard photolithography method using wet etching. Magnetic-field-dependent avalanche breakdown phenomena were observed in the current–voltage curves measured under magnetic field. The avalanche breakdown due to impact ionization was postponed to higher electrical field under applied magnetic field. Accordingly, threshold voltages of avalanche breakdown increased with the applied magnetic field. Above 0.2 T, avalanche breakdown was totally quenched. When Au‐SI‐GaAs Schottky diode was operated above the threshold voltage, giant mangetoresistive effects up to 100 000% were achieved under magnetic field of 0.8 T.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
75.47.De Giant magnetoresistance
73.40.Ns Metal-nonmetal contacts
72.20.Ht High-field and nonlinear effects

Comparison of ac susceptibility of YBa2Cu3O7 coated conductors and single crystals

D.-X. Chen, E. Pardo, A. Sanchez, A. Palau, T. Puig, and X. Obradors

Appl. Phys. Lett. 85, 5646 (2004); http://dx.doi.org/10.1063/1.1833568 (3 pages) | Cited 13 times

Online Publication Date: 8 December 2004

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The complex ac susceptibility of YBa2Cu3O7 (YBCO) coated conductor and YBCO single crystal has been measured at 77 K as a function of field amplitude and frequency, from which the E(J) characteristic is deduced. It is shown that the E(J) in the single crystal obeys a power law in a large range above Ec=1 μV∕cm, indicating a flux creep mechanism, whereas for the coated conductor there appears a transition from flux creep to flux flow at E∼10Ec. The reported contactless technique may be conveniently used for the research and development of coated conductors.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.F- Transport properties
74.20.-z Theories and models of superconducting state
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