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15 Sep 2003

Volume 83, Issue 11, pp. 2091-2291

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 2244 (2003); http://dx.doi.org/10.1063/1.1610259 (3 pages)

X.-M. Meng, Y. Jiang, J. Liu, C.-S. Lee, I. Bello, and S.-T. Lee
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Microwave distribution in stacked Bi2Sr2CaCu2O8+x intrinsic Josephson junctions in a transmission-line geometry

Myung-Ho Bae, Hu-Jong Lee, Jinhee Kim, and Kyu-Tae Kim

Appl. Phys. Lett. 83, 2187 (2003); http://dx.doi.org/10.1063/1.1610258 (3 pages) | Cited 4 times

Online Publication Date: 9 September 2003

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The microwave distribution inside a rectangular stack (15 μm×0.72 μm×60 nm) of Bi2Sr2CaCu2O8+x intrinsic Josephson junctions (IJJs) was studied. The stack was microfabricated into a transmission-line geometry, with a-few-hundred-nm-thick Au layers deposited on the top and bottom of the stack. The microwave distribution was monitored by measuring the anomalous suppression of the tunneling critical current of the IJJs with varied microwave power at frequencies in the W band. This technique can provide valuable information on the microwave transmission modes inside the sandwiched stack of IJJs, which is utterly important for the high-frequency device applications using IJJs, such as fluxon-flow THz oscillators. © 2003 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
84.40.Az Waveguides, transmission lines, striplines
74.72.-h Cuprate superconductors
74.25.N- Response to electromagnetic fields
74.25.Sv Critical currents

Local thermometry technique based on proximity-coupled superconductor/normal-metal/superconductor devices

Z. Jiang, H. Lim, V. Chandrasekhar, and J. Eom

Appl. Phys. Lett. 83, 2190 (2003); http://dx.doi.org/10.1063/1.1611259 (3 pages) | Cited 8 times

Online Publication Date: 9 September 2003

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In mesoscopic superconductor/normal-metal/superconductor heterostructures, it is known that the resistance of the normal metal between the superconductors has a strong temperature dependence. Based on this phenomenon, we have developed a type of thermometer, which dramatically enhances our ability to measure the local electron temperature Te at low temperatures. Using this technique, we have been able to measure small temperature gradients across a micron-size sample, opening up the possibility of quantitatively measuring the thermal properties of mesoscopic devices. © 2003 American Institute of Physics.
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07.20.Dt Thermometers
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
85.25.Cp Josephson devices

Meissner state of high-Tc oxide thin films observed by scanning superconducting quantum interference device microscopy

I. Iguchi, T. Takeda, A. Sugimoto, T. Imaizumi, H. Haibara, and T. Kawai

Appl. Phys. Lett. 83, 2193 (2003); http://dx.doi.org/10.1063/1.1599624 (3 pages)

Online Publication Date: 9 September 2003

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The magnetic level of the Meissner state in high-Tc oxide thin films is investigated using scanning superconducting quantum interference device microscopy. We find that the Meissner level observed is not uniquely determined and shifts with the temperature and depends on the doping level of individual oxide films. The result at higher temperature may be interpreted by a grain-coupled model which reflects the granular nature of high-Tc oxides and is useful for evaluation of high-Tc film quality. © 2003 American Institute of Physics.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Promotion of L10 ordered phase transformation by the Ag top layer on FePt thin films

Z. L. Zhao, J. Ding, K. Inaba, J. S. Chen, and J. P. Wang

Appl. Phys. Lett. 83, 2196 (2003); http://dx.doi.org/10.1063/1.1611280 (3 pages) | Cited 42 times

Online Publication Date: 9 September 2003

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The influence of the deposition of an ultrathin Ag top layer on the structure and magnetic properties of FePt thin films has been investigated. Crystallographic ordering of the L10 face-centered-tetragonal (fct) FePt phase was significantly promoted when a Ag layer was deposited on top of the film. The increased fraction of hard magnetic L10 fct FePt phase led to a dramatic increase of coercivity from 1 to about 6.0 kOe. The δM curves suggested exchange decoupling of magnetic grains. A perpendicular FePt film with a coercivity of 5.0 kOe and remanent squareness of 0.98 was achieved with a CrRu underlayer and the Ag top layer. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.Nq Composition and phase identification
68.35.Rh Phase transitions and critical phenomena
75.30.Et Exchange and superexchange interactions

Co-doped La0.5Sr0.5TiO3−δ: Diluted magnetic oxide system with high Curie temperature

Y. G. Zhao, S. R. Shinde, S. B. Ogale, J. Higgins, R. J. Choudhary, V. N. Kulkarni, R. L. Greene, T. Venkatesan, S. E. Lofland, C. Lanci, J. P. Buban, N. D. Browning, S. Das Sarma, and A. J. Millis

Appl. Phys. Lett. 83, 2199 (2003); http://dx.doi.org/10.1063/1.1610796 (3 pages) | Cited 29 times

Online Publication Date: 9 September 2003

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Ferromagnetism is observed at and above room temperature in pulsed laser deposited epitaxial films of Co-doped Ti-based oxide perovskite (La0.5Sr0.5TiO3−δ). The system has the characteristics of an intrinsic diluted magnetic semiconductor (metal) at low concentrations (< ∼ 2%), but develops inhomogeneity at higher cobalt concentrations. The films range from being opaque metallic to transparent semiconducting depending on the oxygen pressure during growth and are yet ferromagnetic. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Pp Magnetic semiconductors
81.15.Fg Pulsed laser ablation deposition
75.50.Dd Nonmetallic ferromagnetic materials

Indirect exchange coupling between two ferromagnetic electrodes through ZnS barrier in magnetic tunnel junctions

A. Dinia, P. Carrof, G. Schmerber, and C. Ulhacq

Appl. Phys. Lett. 83, 2202 (2003); http://dx.doi.org/10.1063/1.1610257 (3 pages)

Online Publication Date: 9 September 2003

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Room- and low-temperature magnetization measurements have been performed on magnetic tunnel junctions before patterning to evidence the presence of an indirect ferromagnetic exchange interaction between the hard and the soft ferromagnetic electrodes through the ZnS barrier. The magnetic junctions are composed of an artificial ferrimagnet CoFe/Ru/CoFe sandwich as a hard layer separated by a ZnS barrier from a soft CoFe/Fe soft layer as follows: Fe6 nmCu3 nm(CoFe)1.8 nmRu0.8 nm(CoFe)3 nmZnSx nmCoFe1 nmFe4 nmCu1 nmRu3 nm. At room temperature, a large shift of about −25 Oe is observed in a magnetization minor loop that indicates the presence of a ferromagnetic interaction. The decrease of the amplitude of this shift at low temperature provides a signature of an indirect exchange coupling mediated by spin-polarized quantum tunneling. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ww Permanent magnets

Current-induced precessional magnetization reversal

H. W. Schumacher, C. Chappert, R. C. Sousa, and P. P. Freitas

Appl. Phys. Lett. 83, 2205 (2003); http://dx.doi.org/10.1063/1.1610797 (3 pages) | Cited 8 times

Online Publication Date: 9 September 2003

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We report magnetization reversal in microscopic current-in-plane spin valves by ultrashort current pulses through the device. Current densities of the order of 1011 A/m2 with pulse durations as short as 120 ps reliably and reversibly switch the cell’s free-layer magnetization. Variations of the pulse parameters reveal the full signature of precessional switching, which is triggered by the transverse magnetic field generated by the device current. This current switching mode allows for the design of a two-terminal nonvolatile magnetic memory cell combining ultrafast access times and high magnetoresistive readout. © 2003 American Institute of Physics.
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75.60.Jk Magnetization reversal mechanisms
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.75.Bb Magnetic memory using giant magnetoresistance

Microchemistry and magnetization reversal mechanism in melt-spun 2:17-type Sm-Co magnets

A. Yan, O. Gutfleisch, T. Gemming, and K.-H. Müller

Appl. Phys. Lett. 83, 2208 (2003); http://dx.doi.org/10.1063/1.1611641 (3 pages) | Cited 12 times

Online Publication Date: 9 September 2003

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The stability of microstructure and of microchemistry in melt-spun precipitation-hardened Sm(Co,Fe,Cu,Zr)z magnets at high temperature and its effect on the magnetic properties, especially the coercivity at room temperature, were investigated by transmission electron microscopy, nanoprobe chemical analysis, and magnetic measurements. A very large gradient of the Cu content within the 1:5-type cell boundary phase was observed in highly coercive melt-spun Sm(Co,Fe,Cu,Zr)z magnets with uniform cellular structure. After an additional isothermal aging at 850 °C for 5 min, the coercivity is reduced dramatically from 3 T to 0.16 T. This is accompanied by the disappearance of the large gradient of Cu content within the cell boundary phase. Thus, it is proposed that the high coercivity in 2:17 Sm-Co magnets originates from the large gradient of domain wall energy within the Sm(Co,Cu)5 cell boundary phase. This gradient is caused by a very rapid phase separation taking place within the cell boundary phase during slow cooling. © 2003 American Institute of Physics.
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75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials
75.50.Bb Fe and its alloys
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
75.60.Ch Domain walls and domain structure
64.75.-g Phase equilibria
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