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11 Aug 2003

Volume 83, Issue 6, pp. 1063-1275

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 1163 (2003); http://dx.doi.org/10.1063/1.1599972 (3 pages)

M. C. Rogge, C. Fühner, U. F. Keyser, R. J. Haug, M. Bichler, G. Abstreiter, and W. Wegscheider
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Anomalous temperature dependence of coercivity in precipitation hardened Pr–Co–Cu–Ti magnets

Jian Zhang, Hui Liu, Chuan-bin Rong, Hong-wei Zhang, Shao-ying Zhang, Bao-gen Shen, Yuan-qiang Bai, and Bao-he Li

Appl. Phys. Lett. 83, 1172 (2003); http://dx.doi.org/10.1063/1.1597747 (3 pages) | Cited 9 times

Online Publication Date: 5 August 2003

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The anomalous temperature dependence of coercicity, Hc(T), has been observed in precipitation hardened PrCo6.7−xCuxTi0.3 (x = 0.2–1) magnets. Transmission electron microscopy reveals that they exhibit a cellular microstructure. With an increase of Cu content, the Curie temperature of the 2:17 phase remains nearly unchanged whereas that of the 1:5 phase decreases. The peak of Hc(T) becomes higher, broader and shifts towards low temperature while the room temperature coercivity remains low and does not change with an increase of Cu content. There is a strong correlation between the Curie temperature of the 1:5 phase and the peak of Hc(T). The effect of Cu on Hc(T) cannot be explained by a traditional domain wall pinning model. It is highly likely that their magnetization reversal is controlled by the nucleation of reverse domains in isolated 2:17 cells. © 2003 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
75.50.Vv High coercivity materials
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.50.Cc Other ferromagnetic metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure

Dynamic orientation ratio in longitudinal recording media

S. N. Piramanayagam, J. H. Yin, H. B. Zhao, J. Kasim, Y. J. Chen, J. Zhang, and C. H. Hee

Appl. Phys. Lett. 83, 1175 (2003); http://dx.doi.org/10.1063/1.1599045 (3 pages) | Cited 1 time

Online Publication Date: 5 August 2003

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The origin of orientation ratio (OR) in longitudinal recording media has been controversial in the literature. In the past, the observation of a higher OR for thinner magnetic films has been attributed to stress or thermal effects. Our measurements, carried out over a larger range of time scales, confirm that the thermal effects play a major role in the observation of a higher OR for thinner magnetic films. We point out that the OR is dynamic and follows a ln(t) behavior at larger time scales (5–1000 s). Our studies indicate that a larger OR and a more dynamic behavior of OR will be observed when KuV/kBT values are smaller. We also propose that the slope of dynamic OR can be used to compare the recording performance of media indirectly. © 2003 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.70.Ak Magnetic properties of monolayers and thin films

Electronic structures of two-phase microstructures α and β in heavily Pb-doped Bi2Sr2CaCu2Oy single crystals investigated by scanning tunneling microscopy/spectroscopy

G. Kinoda, T. Hasegawa, S. Nakao, T. Hanaguri, K. Kitazawa, K. Shimizu, J. Shimoyama, and K. Kishio

Appl. Phys. Lett. 83, 1178 (2003); http://dx.doi.org/10.1063/1.1594826 (3 pages) | Cited 8 times

Online Publication Date: 5 August 2003

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We have performed scanning tunneling microscopy/spectroscopy (STM/STS) of a high-Jc superconductor, heavily Pb-doped Pb0.6Bi1.4Sr2CaCu2Oy, at low temperatures below Tc. The obtained STM images showed a lamella-type phase separation into Pb-poor and Pb-rich regions. At 4.3 K, values of energy gap Δ, deduced from STS spectra, showed considerable inhomogeneity in the range of 20–80 meV, while Δ variations across the phase boundaries were less significant. At 63 K, in contrast, we found that Δ altered sharply at the boundaries particularly in the annealed samples, resulting from the suppression of electronic inhomogeneity in each phase. This suggests that the phase boundaries act as strong pinning centers at higher temperatures. © 2003 American Institute of Physics.
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74.25.Jb Electronic structure (photoemission, etc.)
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Microstructure and high critical current density of in situ processed MgB2 tapes made by WSi2 and ZrSi2 doping

Yanwei Ma, H. Kumakura, A. Matsumoto, and K. Togano

Appl. Phys. Lett. 83, 1181 (2003); http://dx.doi.org/10.1063/1.1600508 (3 pages) | Cited 23 times

Online Publication Date: 5 August 2003

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WSi2- and ZrSi2-doped Fe-sheathed MgB2 tapes were prepared through the in situ powder-in-tube method. Both WSi2- and ZrSi2-doped tapes were found to have significantly increased critical current density Jc at 4.2 K in magnetic fields up to 12 T than their undoped counterpart. Scanning electron microscopy investigation revealed that the WSi2 and ZrSi2, doping enhanced intergranular connectivity, thus raising Jc by more than a factor of 2.2 and 3.4, respectively. Moreover, the critical temperature for the doped tapes decreased slightly (less than 0.7 K). It was also found that the improved field dependence of the WSi2 tapes was due to the pinning by possible segregates or defects caused by the WSi2 addition. This role of WSi2 and ZrSi2 may be very beneficial in the fabrication of MgB2 tapes for a large range of applications. © 2003 American Institute of Physics.
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74.10.+v Occurrence, potential candidates
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.62.Dh Effects of crystal defects, doping and substitution
84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents
74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)
61.72.-y Defects and impurities in crystals; microstructure
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Nanoscale observation of room-temperature ferromagnetism on ultrathin (La,Ba)MnO3 films

Teruo Kanki, Run-Wei Li, Yasuhisa Naitoh, Hidekazu Tanaka, Takuya Matsumoto, and Tomoji Kawai

Appl. Phys. Lett. 83, 1184 (2003); http://dx.doi.org/10.1063/1.1599971 (3 pages) | Cited 21 times

Online Publication Date: 5 August 2003

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We have fabricated La0.8Ba0.2MnO3 ultrathin films with an atomically flat surface and have systematically investigated the magnetism for film thickness dependence. The 20-nm-thick film showed a maximum peak of TC (310 K). It was found that even the 5-nm-thick film showed a TC of 290 K near room temperature, which opens up the possibility of spin devices working at room temperature. Furthermore, we have adopted noncontact magnetic force microscopy to evaluate local magnetization in ultrathin (La,Ba)MnO3 films, and confirmed that several tens of nanocale ferromagnetic domains appear at room temperature. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Rt Magnetic force microscopy (MFM)
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