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15 Nov 1999

Volume 75, Issue 20, pp. 3051-3226

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Thermomagnetic writing on 29 Gbit/in.2 patterned magnetic media

Chiseki Haginoya, Kazuyuki Koike, Yoshiyuki Hirayama, Jiro Yamamoto, Masayoshi Ishibashi, Osamu Kitakami, and Yutaka Shimada

Appl. Phys. Lett. 75, 3159 (1999); http://dx.doi.org/10.1063/1.125263 (3 pages) | Cited 16 times

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We have demonstrated a thermomagnetic writing on a 29 Gbit/in.2 patterned medium with perpendicular magnetic anisotropy, by using Joule heat produced by a current flowing between a magnetic dot in the medium and a magnetic force microscope tip. The possible application of this thermomagnetic method to future patterned media is also discussed. © 1999 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.30.Sg Magnetocaloric effect, magnetic cooling

Structural and magnetic properties of FePt:SiO2 granular thin films

C. P. Luo and D. J. Sellmyer

Appl. Phys. Lett. 75, 3162 (1999); http://dx.doi.org/10.1063/1.125264 (3 pages) | Cited 92 times

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Nanocomposite FePt:SiO2 films have been fabricated by annealing the as-deposited FePt/SiO2 multilayers at temperatures from 450 to 650 °C. These films consist of high-anisotropy tetragonal L10 FePt particles embedded in a SiO2 matrix. The structural and magnetic properties of these films were investigated. We have found that coercivity and grain size are highly dependent on the annealing temperature and SiO2 concentration. Films with coercivities in the range from 2 to 8 kOe and grain sizes of 10 nm or less were obtained. These films have considerable potential as high-density magnetic recording media. © 1999 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ss Magnetic recording materials
61.72.Cc Kinetics of defect formation and annealing
75.50.Vv High coercivity materials
75.70.Ak Magnetic properties of monolayers and thin films

High coercivity in nanostructured PrCo5-based powders produced by mechanical milling and subsequent annealing

Zhongmin Chen, X. Meng-Burany, and G. C. Hadjipanayis

Appl. Phys. Lett. 75, 3165 (1999); http://dx.doi.org/10.1063/1.125265 (3 pages) | Cited 24 times

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Nanostructured PrCo5-based PrxCo100−x (x = 15.4–20.5) powders have been synthesized by mechanical milling and subsequent annealing cast alloys. The best overall properties have been developed in stoichiometric PrCo5 powders milled for 4 h and annealed at 800 °C for 1 min with a high coercivity of 16.3 kOe along with a high Mr/Ms ratio of 0.66 and medium-strength maximum-energy product of 11.6 MGOe. The highest coercivity of 23.7 kOe has been obtained in Pr19Co81 powders. Microstructural studies reveal that a uniform PrCo5 microstructure with an average grain size of about 15 nm is developed in the powders, which have an average particle size of about 5 μm. The observed magnetic hardening is believed to arise from the high anisotropy field of the PrCo5 phase and the uniform nanoscale microstructure developed by the processing used. © 1999 American Institute of Physics.
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75.50.Ww Permanent magnets
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys
81.20.Wk Machining, milling
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.05.Bx Metals, semimetals, and alloys
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
61.43.Gt Powders, porous materials

The use of the in-field critical current density, Jc(0.1 T), as a better descriptor of (Bi, Pb)2Sr2Ca2Cu3Ox/Ag tape performance

L. A. Schwartzkopf, J. Jiang, X. Y. Cai, D. Apodaca, and D. C. Larbalestier

Appl. Phys. Lett. 75, 3168 (1999); http://dx.doi.org/10.1063/1.125266 (3 pages) | Cited 11 times

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Extended voltage–current characteristics of 13 optimized (Bi, Pb)2Sr2Ca2Cu3Ox/Ag multifilamentary tapes from four different manufacturers were extensively evaluated so as to extract the field-dependent Jc(H), the characteristic field Hp obtained from the relation Jc ∼ exp(−H/Hp), and the irreversibility field H∗. Values of the self-field critical current density Jc(0 T, 77 K) ranged from 12 to 63 kA/cm2, Ic(0 T,77 K) from 11 to 139 A, Hp from 128 to 204 mT, and H∗ from 163 to 369 mT, this range thus being representative of present optimized composites. Self-field can strongly dominate Jc(H) in fields below 20 mT; thus, Jc(0 T,77 K) is a flawed parameter for characterizing tapes because of its very heavy dependence on self-field. We propose that a much better descriptor of tape performance is Jc(0.1 T,77 K), because it lies outside the self-field and weak-link-destruction regimes and clearly within the flux-pinning-controlled domain where the connectivity-determined active cross-section carrying current is constant. © 1999 American Institute of Physics.
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74.72.-h Cuprate superconductors
84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents
74.25.Ha Magnetic properties including vortex structures and related phenomena

Observation of strong to Josephson-coupled crossover in 10° YBa2Cu3Ox bicrystal junctions

R. D. Redwing, B. M. Hinaus, M. S. Rzchowski, N. F. Heinig, B. A. Davidson, and J. E. Nordman

Appl. Phys. Lett. 75, 3171 (1999); http://dx.doi.org/10.1063/1.125267 (3 pages) | Cited 16 times

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A temperature-dependent strong to weak (Josephson) coupling crossover near 75 K is observed for 10° misorientation YBa2Cu3Ox grain boundaries. Below 75 K the current–voltage characteristic (IVC) shows strongly coupled, flux-flow behavior. Above 75 K, the IVC is Josephson coupled. The data are consistent with a network of microbridges at the grain boundary defined by dislocation strain fields. The data are compared to recent calculations by A. Gurevich and A. E. Pashitskii [Phys. Rev. B 57, 13878 (1998)]. The characteristic voltages for these low-angle grain boundaries are higher than high-angle boundaries at 77 K, and could lead to improved high-temperature superconducting device operation in this temperature range. © 1999 American Institute of Physics.
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74.72.-h Cuprate superconductors
61.72.Mm Grain and twin boundaries
74.50.+r Tunneling phenomena; Josephson effects
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Room-temperature perpendicular magnetic anisotropy in Ni/Pd (111) multilayers

Jong-Ryul Jeong and Sung-Chul Shin

Appl. Phys. Lett. 75, 3174 (1999); http://dx.doi.org/10.1063/1.125268 (3 pages) | Cited 10 times

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We report the experimental observation of room-temperature perpendicular magnetic anisotropy (PMA) in Ni/Pd (111) multilayer films having the thickness range of 5–11 Å Ni and 4–11 Å Pd sublayers, prepared by direct current magnetron sputtering on glass substrates at Ar sputtering pressure of 7 mTorr. Perpendicular magnetic anisotropy was found to be sensitively dependent on both Ni- and Pd-sublayer thicknesses, and a maximum anisotropy energy of 5.6×105 erg/cm3 was obtained for the (5 Å Ni/6 Å Pd)30 multilayer. The magnetoelastic anisotropy, quantitatively determined from in situ stress and ex situ magnetostriction coefficient measurements, was found to play an important role for the observed PMA in this system, together with the surface anisotropy. © 1999 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
75.80.+q Magnetomechanical effects, magnetostriction
75.70.Rf Surface magnetism

Room-temperature coercivity enhancement in mechanically alloyed antiferromagnetic-ferromagnetic powders

J. Sort, J. Nogués, X. Amils, S. Suriñach, J. S. Muñoz, and M. D. Baró

Appl. Phys. Lett. 75, 3177 (1999); http://dx.doi.org/10.1063/1.125269 (3 pages) | Cited 47 times

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The coercivity, HC, and squareness of Co powders have been enhanced at room temperature by mechanically alloying them with antiferromagnetic powders with Néel temperature, TN, above room temperature. The enhancement is maximum after field annealing above TN. The existence of loop shifts and the dependence of HC on the annealing and measuring temperatures indicate that exchange bias effects are responsible for this behavior. © 1999 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
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