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25 Sep 2006

Volume 89, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 89, 131108 (2006); http://dx.doi.org/10.1063/1.2356892 (3 pages)

Paul E. Barclay, Kartik Srinivasan, Oskar Painter, Benjamin Lev, and Hideo Mabuchi
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Magnetic properties of layered nanorings

J. Escrig, P. Landeros, D. Altbir, M. Bahiana, and J. d’Albuquerque e Castro

Appl. Phys. Lett. 89, 132501 (2006); http://dx.doi.org/10.1063/1.2356692 (3 pages) | Cited 10 times

Online Publication Date: 25 September 2006

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The magnetic structure of nanorings consisting of alternate layers of magnetic and nonmagnetic materials is investigated as a function of their geometry. Phase diagrams giving the relative stability of characteristic internal magnetic configurations of the rings are obtained. Attention is focused on the condition for occurrence of the vortex configurations, in which case the layered structure might be used to produce magnetoresistive random access memories.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
84.30.Sk Pulse and digital circuits
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.50.Tt Fine-particle systems; nanocrystalline materials

L10 ordered epitaxial FePt (001) thin films on TiN/Si (100) by pulsed laser deposition

G. R. Trichy, J. Narayan, and H. Zhou

Appl. Phys. Lett. 89, 132502 (2006); http://dx.doi.org/10.1063/1.2357848 (3 pages) | Cited 6 times

Online Publication Date: 26 September 2006

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Epitaxially oriented magnetic FePt (001) thin films were grown on Si (001) substrates with TiN as a template buffer by using pulsed laser deposition. The epitaxial relationship and presence of L10 ordering were studied by x-ray diffraction and further confirmed by detailed transmission electron microscopy. The effectiveness of using TiN (diamagnetic metal) as a template, for an epitaxial magnetic FePt heterostructure integrated with silicon and for inducing L10 order in the FePt films, has been demonstrated. Magnetic measurements show that the ordered FePt films are predominantly perpendicularly magnetized and have high values of coercivity suitable for magnetic recording applications.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ss Magnetic recording materials
75.50.Bb Fe and its alloys
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth

Ferromagnetism in Mn-doped GaN nanocrystals prepared solvothermally at low temperatures

Kanishka Biswas, Kripasindhu Sardar, and C. N. R. Rao

Appl. Phys. Lett. 89, 132503 (2006); http://dx.doi.org/10.1063/1.2357927 (3 pages) | Cited 17 times

Online Publication Date: 26 September 2006

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3% and 5% Mn-doped GaN nanocrystals of different sizes, with the average diameters in the range of 4–18 nm, have been prepared by two independent routes under solvothermal conditions starting with two different precursors. The reaction temperature was around 350 °C in all the preparations. The nanocrystals so prepared exhibit ferromagnetism with magnetization (M) and Curie temperature (TC) values increasing with percent of Mn and particle size. The observation of ferromagnetism in Mn-doped GaN nanocrystals prepared at relatively low temperatures is of significance in understanding this potential in spintronics materials.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Enhanced microwave absorption in nickel/hexagonal-ferrite/polymer composites

Bao-Wen Li, Yang Shen, Zhen-Xing Yue, and Ce-Wen Nan

Appl. Phys. Lett. 89, 132504 (2006); http://dx.doi.org/10.1063/1.2357565 (3 pages) | Cited 23 times

Online Publication Date: 27 September 2006

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Ni/hexagonal-ferrite (Co2Z or Zn2Y barium ferrites)/polymer composites were prepared for electromagnetic interference (EMI) shielding materials. In comparison with the hexagonal-ferrite/polymer or Ni/polymer composites, such three-phase composites exhibit excellent microwave absorption properties in the X-band frequency range, strongly depending on the combination of these three phases. For the Ni/Co2Z/polymer composites with volume fraction ratio of Ni/ferrite equal to 0.70/0.30, the EMI shielding effectiveness (SE) of the composites with a thickness of 2 mm can be as high as ∼ 67 dB. The high EMI SE of the composites and much larger contribution to total EMI SE from absorption than from reflection suggest that these composites would be very promising for applications as thinner and lighter EMI absorption materials.
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78.70.Gq Microwave and radio-frequency interactions

Development of textured MgO templates on nonmetallic flexible ceraflex

Rongtao Lu, Ronald N. Vallejo, Daniel W. Fisher, and Judy Z. Wu

Appl. Phys. Lett. 89, 132505 (2006); http://dx.doi.org/10.1063/1.2357849 (3 pages) | Cited 3 times

Online Publication Date: 27 September 2006

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Reducing ac loss has become a critical issue in the development of high-Tc superconductor coated conductors (HTSCCs). One scheme is to replace the metallic substrates employed currently for HTSCCs with nonmetallic ones. The flexible ceramic polycrystalline ceraflex is a promising candidate while its rough surface presents a tough challenge in the development of textured templates needed for HTSCCs. By developing a surface smoothening process, high-quality biaxially textured MgO templates have been achieved on ceraflex. This work has overcome the major difficulties in texturing ceraflex surface for HTSCCs, which may provide a viable scheme for low ac loss HTSCC applications.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness
81.65.-b Surface treatments

Magnetic manipulation of materials in a magnetic ionic liquid

Masanari Okuno, Hiro-o Hamaguchi, and Satoshi Hayashi

Appl. Phys. Lett. 89, 132506 (2006); http://dx.doi.org/10.1063/1.2353808 (2 pages) | Cited 25 times

Online Publication Date: 27 September 2006

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Nonmagnetic materials in a magnetic ionic liquid, which has a very large magnetic susceptibility, respond to a magnet as if they are strongly diamagnetic. The trajectory of deflected nitrogen gas bubbles in 1-butyl-3-methylimidazolium tetrachloroferrate has been measured. It shows a good agreement with theory. Nonmagnetic materials can be transported and separated in a magnetic ionic liquid, according to their density and magnetic susceptibility by regulating magnetic field and its gradient.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Mm Magnetic liquids
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism

High magnetoresistance and low coercivity in electrodeposited Co/Cu granular multilayers

S. K. Ghosh, A. K. Grover, P. Chowdhury, S. K. Gupta, G. Ravikumar, D. K. Aswal, M. Senthil Kumar, and R. O. Dusane

Appl. Phys. Lett. 89, 132507 (2006); http://dx.doi.org/10.1063/1.2357014 (3 pages) | Cited 11 times

Online Publication Date: 28 September 2006

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Co/Cu multilayers were electrodeposited from a single solution electrolyte. By reducing the magnetic layer thickness from 1 to 0.2 nm, samples with heterogeneous mixture of ferromagnetic and superparamagnetic clusters have been made. Magnetization and magnetotransport measurements revealed the structured evolution of the multilayer granular samples. With critical thickness of tCo ∼ 0.5 nm, room temperature magnetoresistance of 7% was obtained at 2 kOe with hysteresis of 70 Oe. The large magnetoresistance obtained in granular multilayers is attributed to the presence of a range of sizes for the Co particles.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Np Metals and alloys
75.50.Cc Other ferromagnetic metals and alloys
75.47.De Giant magnetoresistance
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.20.En Metals and alloys
81.15.Pq Electrodeposition, electroplating

Evaluation of connectivity, flux pinning, and upper critical field contributions to the critical current density of bulk pure and SiC-alloyed MgB2

A. Matsumoto, H. Kumakura, H. Kitaguchi, B. J. Senkowicz, M. C. Jewell, E. E. Hellstrom, Y. Zhu, P. M. Voyles, and D. C. Larbalestier

Appl. Phys. Lett. 89, 132508 (2006); http://dx.doi.org/10.1063/1.2357027 (3 pages) | Cited 70 times

Online Publication Date: 28 September 2006

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Measurement of critical current density Jc, normal state resistivity ρn, and upper critical field Hc2 on pure and 10% SiC-doped MgB2 bulks show systematic enhancement of Hc2 by SiC addition and by lowering reaction temperature. Hc2(10 K) exceeds 33 T, while the extrapolated zero temperature value exceeds 40 T. The Rowell [Supercond. Sci. Technol. 16, R17 (2003) ] analysis suggests that only 8%–17% of the MgB2 cross section actually carries current. Higher reaction temperature enhances the connectivity but degrades Hc2 and flux pinning, making the measured Jc a complex balance between connectivity, Hc2, and flux pinning induced by grain boundaries and precipitates.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents
74.25.F- Transport properties
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Op Mixed states, critical fields, and surface sheaths
74.62.Dh Effects of crystal defects, doping and substitution

Effect of interface passivation on the magnetoresistance of granular magnetite Fe3(1−δ)O4

S. I. Rybchenko, Y. Fujishiro, H. Takagi, and M. Awano

Appl. Phys. Lett. 89, 132509 (2006); http://dx.doi.org/10.1063/1.2357581 (3 pages) | Cited 6 times

Online Publication Date: 28 September 2006

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The reductive passivation of granular interface was proposed to enhance the tunneling magnetoresistance of bulk granular magnetite. For this, an annealing in paraffin wax has been applied. As a result, the low-field magnetoresistance response was increased up to 8% at 300 K and 32% at 130 K. The effect is attributed to the passivation-induced depletion of density of the tunneling-active spin-depolarized interface states. The obtained results indicate the important role of interface states in tunneling contacts with magnetite electrodes and suggest a way to control these states.
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81.05.Rm Porous materials; granular materials
75.47.Pq Other materials
81.65.Rv Passivation
81.40.Gh Other heat and thermomechanical treatments
73.20.At Surface states, band structure, electron density of states

Improved critical current densities in MgB2 tapes with ZrB2 doping

Xianping Zhang, Zhaoshun Gao, Dongliang Wang, Zhengguang Yu, Yanwei Ma, S. Awaji, and K. Watanabe

Appl. Phys. Lett. 89, 132510 (2006); http://dx.doi.org/10.1063/1.2357884 (3 pages) | Cited 8 times

Online Publication Date: 28 September 2006

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MgB2/Fe tapes with 2.5–15 at. % ZrB2 additions were prepared through the in situ powder-in-tube method. The phases, microstructures, critical current density, and flux pinning were characterized by means of x-ray diffraction, scanning electron microscope, and magnetic and transport property measurements. Compared to the pure tape, a significant improvement in the in-field JC was observed for all the ZrB2 doped samples, while the critical temperature decreased slightly. The highest JC value was achieved for the 10 at. % doped sample. At 4.2 K, the transport JC increased by more than an order of magnitude than the undoped one in magnetic fields above 9 T. Nanoscale segregates or defects caused by the ZrB2 additions which act as effective flux pinning centers are proposed to be the main reasons for the improved JC field performance.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.10.+v Occurrence, potential candidates

Exchange spring driven spin flop transition in ErFe2/YFe2 multilayers

K. N. Martin, K. Wang, G. J. Bowden, A. A. Zhukov, P. A. J. de Groot, J. P. Zimmermann, H. Fangohr, and R. C. C. Ward

Appl. Phys. Lett. 89, 132511 (2006); http://dx.doi.org/10.1063/1.2357918 (3 pages) | Cited 5 times

Online Publication Date: 29 September 2006

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Magnetization loops for (110) ErFe2/YFe2 multilayer films grown by molecular beam epitaxy are presented and discussed. The direction of easy magnetization for the Er layers is out of plane, near a ⟨111⟩-type crystal axis. For fields applied along the (110) crystal growth axis, out-of-plane magnetic exchange springs are set up in the magnetically soft YFe2 layers. For multilayer films that display negative coercivity at low temperatures, there is a crossover temperature above which the coercivity becomes positive, with additional transitions at high fields. These features are interpreted using micromagnetic modeling. At sufficiently high fields, applied perpendicular to the multilayer film plane, the energy is minimized by an exchange spring driven multilayer spin flop. In this state, the average magnetization of the ErFe2 layers switches into a nominally hard in-plane ⟨111⟩ axis, perpendicular to the applied field.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Bb Fe and its alloys
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