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22 Jan 2007

Volume 90, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 90, 043507 (2007); http://dx.doi.org/10.1063/1.2435508 (3 pages)

D. Y. Kim and A. J. Steckl
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Silicon oil: A cheap liquid additive for enhancing in-field critical current density in MgB2

X. L. Wang, Z. X. Cheng, and S. X. Dou

Appl. Phys. Lett. 90, 042501 (2007); http://dx.doi.org/10.1063/1.2435321 (3 pages) | Cited 24 times

Online Publication Date: 23 January 2007

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In this work, the authors report on significant flux pinning enhancement in MgB2 that has been easily obtained using a liquid additive, silicon oil. MgB2 bulk samples with 0 up to 30 wt % silicon oil added were prepared by an in situ reaction. Results showed that the Si and C released from the decomposition of the silicon oil formed Mg2Si and substituted into B sites, respectively. Increasing the amount of the Si oil up to 15 wt % has resulted in the reduction of the lattice parameters, as well as Tc and R(300 K)/R(Tc) values, accompanied by a significant enhancement of Jc(H), Hirr, and Hc2.
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74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
61.66.Fn Inorganic compounds
61.72.up Other materials

Structure and magnetic transport properties of Ge doped La(Co,Si)13 intermetallics

Yongquan Guo and Wei Li

Appl. Phys. Lett. 90, 042502 (2007); http://dx.doi.org/10.1063/1.2435331 (3 pages)

Online Publication Date: 23 January 2007

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The crystal structure and the magnetic and electronic transport properties of Ge doped LaCo10.5Si2.5−xGex (x = 0–0.3) intermetallics have been investigated using powder x-ray diffraction and magnetic and electrical measurements. According to the x-ray diffraction pattern analysis, Ge as a dopant decreases the stability of the cubic LaCo 1:13 phase and stabilizes the Si based La(Co,Si) 1:13 tetragonal phase. From the authors’ structural refinement, the authors found that Ge prefers to occupy the 16l(2) position in the tetragonal phase. LaCo10.5Si2.2Ge0.3 shows ferromagnetic order with a metamagnetic state around 350 K. An anomaly in resistivity is observed at around 367 K, which is associated with the metamagnetic transition. The resistivity follows ρ(T) = ρo+aTn rule in the temperature range of 4–400 K with n = 1.17(3) for the half metallic state and n = 2 for the normal metallic state, respectively. This type of discontinuity can be interpreted as a crossover from a low temperature metamagnetic half metallic state to the normal ferromagnetic-metallic state.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Cc Other ferromagnetic metals and alloys
61.66.Dk Alloys
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Optimizing levitation force and stability in superconducting levitation with translational symmetry

Nuria Del Valle, Alvaro Sanchez, Enric Pardo, Du-Xing Chen, and Carles Navau

Appl. Phys. Lett. 90, 042503 (2007); http://dx.doi.org/10.1063/1.2435940 (3 pages) | Cited 21 times

Online Publication Date: 23 January 2007

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From a theoretical analysis based on an energy minimization procedure and the critical-state model, the authors analyze the levitation of an infinitely long superconductor above infinitely long permanent magnets with different arrangements. A discussion on optimum geometries showing large levitation force and good stability is presented from the model results.
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74.25.Ha Magnetic properties including vortex structures and related phenomena

Ultrafast magnetization dynamics probed by anisotropic magnetoresistance

H. W. Schumacher, S. Serrano-Guisan, K. Rott, and G. Reiss

Appl. Phys. Lett. 90, 042504 (2007); http://dx.doi.org/10.1063/1.2433759 (3 pages) | Cited 4 times

Online Publication Date: 24 January 2007

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The authors use time resolved measurements of the anisotropic magnetoresistance (AMR) to study ultrafast magnetization dynamics of microstructured disks of Permalloy. The devices show an AMR of the order of 0.25% revealing the characteristic cos2 angular dependence. From the time resolved AMR the authors derive the in plane angular excursion of the magnetization with angular resolution down to 1°. From the decay of the homogeneous precession the authors derive a Gilbert damping parameter of 0.008±0.001. This technique can be applied to study magnetization precession and damping in individual micropatterned devices of a wide variety of magnetic thin film and multilayer materials.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Np Metals and alloys

Electronic structure and magnetism in compressed 3d transition metals

Valentin Iota, Jae-Hyun Park Klepeis, Choong-Shik Yoo, Jonathan Lang, Daniel Haskel, and George Srajer

Appl. Phys. Lett. 90, 042505 (2007); http://dx.doi.org/10.1063/1.2434184 (3 pages) | Cited 21 times

Online Publication Date: 24 January 2007

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The authors present a systematic study of high-pressure effects on electronic structure and magnetism in 3d transition metals (Fe, Co, and Ni) based on x-ray magnetic circular dichroism measurements. The data show that the net magnetic moment in Fe vanishes above 18 GPa upon the transition to hcp Fe, while both cobalt and nickel remain ferromagnetic to well over 100 GPa. The authors estimate the total disappearance of moment in hcp Co at around 150 GPa and predict a nonmagnetic Ni phase above 250 GPa. The present data suggest that the suppression of ferromagnetism in Fe, Co, and Ni is due to pressure-induced broadening of the 3d valence bands.
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71.20.Be Transition metals and alloys
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
78.20.Ls Magneto-optical effects
75.30.Cr Saturation moments and magnetic susceptibilities
62.50.-p High-pressure effects in solids and liquids

Magnetostatic interactions in patterned CoPt films embedded in a permalloy matrix

S. Schnittger, S. Dreyer, Ch. Jooss, S. Sievers, and U. Siegner

Appl. Phys. Lett. 90, 042506 (2007); http://dx.doi.org/10.1063/1.2435592 (3 pages) | Cited 4 times

Online Publication Date: 24 January 2007

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In order to study magnetostatic interactions in magnetic arrays, a two-dimensional pattern of hard magnetic (001) L10 CoPt squares embedded into a permalloy matrix was fabricated. The structural and magnetic properties of these arrays were characterized by magneto-optical measurements, atomic force and magnetic force microscopies. The hard magnetic squares are not exchange coupled to the soft magnet, yet a magnetostatic coupling was observed. This coupling modifies the domain structure of the permalloy matrix. In periodic arrays of embedded CoPt squares, the stray field interaction induces a long-range ordered domain pattern in the soft magnetic matrix and short-range correlations of edge domains in adjacent CoPt squares.
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75.60.Ch Domain walls and domain structure
75.50.Ww Permanent magnets
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
78.20.Ls Magneto-optical effects
75.50.Cc Other ferromagnetic metals and alloys
81.05.Zx New materials: theory, design, and fabrication

Low-field inverse magnetocaloric effect in Ni50−xMn39+xSn11 Heusler alloys

Z. D. Han, D. H. Wang, C. L. Zhang, H. C. Xuan, B. X. Gu, and Y. W. Du

Appl. Phys. Lett. 90, 042507 (2007); http://dx.doi.org/10.1063/1.2435593 (3 pages) | Cited 75 times

Online Publication Date: 24 January 2007

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The low-field magnetic entropy changes in Ni50−xMn39+xSn11 alloys (x = 5, 6, and 7) were investigated. The martensitic transition shifts to lower temperature with the increase of Mn concentration. Under an applied magnetic field of 10 kOe, the magnetic entropy changes are 6.8, 10.1, and 10.4 J/kg K, for x = 5, 6, and 7, respectively. The large entropy change in Ni50−xMn39+xSn11 can be attributed to the sharp magnetization change associated with the martensitic transition from a ferromagnetic parent phase to a weak-magnetic martensitic phase. The large low-field magnetic entropy change and low cost suggest Ni50−xMn39+xSn11 alloy as the promising magnetic refrigerant.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys
81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions

High coercivity L10 FePt films with perpendicular anisotropy deposited on glass substrate at reduced temperature

J. S. Chen, B. C. Lim, J. F. Hu, Y. K. Lim, B. Liu, and G. M. Chow

Appl. Phys. Lett. 90, 042508 (2007); http://dx.doi.org/10.1063/1.2430910 (3 pages) | Cited 28 times

Online Publication Date: 25 January 2007

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The microstructures and magnetic properties of FePt films grown at 350 °C on glass substrates with MgO (200) intermediate layer and CrRu (200) underlayer were investigated. The film with 1 nm MgO intermediate layer showed higher degree of chemical ordering than that with 4 nm MgO layer due to the compression of the lattice constant of 1 nm MgO intermediate layer along the [100] direction. Isolated FePt particles were formed when nominal thickness of FePt was 4 nm. The room temperature coercivity of isolated FePt particles with 1 nm MgO intermediate layer was as high as 12 kOe, significantly larger than that with 4 nm MgO intermediate layer (6.3 kOe).
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75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.-a Thin film structure and morphology

Ion irradiation and thermally induced mixing of CoCrPt/Cr multilayered films

M. T. Georgieva, P. J. Grundy, and N. D. Telling

Appl. Phys. Lett. 90, 042509 (2007); http://dx.doi.org/10.1063/1.2432256 (3 pages) | Cited 3 times

Online Publication Date: 26 January 2007

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A set of CoCrPt/Cr multilayered films with variable layer thicknesses has been used in an investigation of interlayer mixing and “patterning” of samples with relatively high coercivity and in-plane magnetization. The multilayers with the highest coercivities were irradiated with different doses of Ar++ ions in order to intermix the Cr and CoCrPt layers and push the CoCrPt stoichiometry into the nonmagnetic region of the phase diagram. Samples were also irradiated through a Ni-grating mask to obtain patterning by adjacent magnetic and nonmagnetic regions of the film. Thermal annealing experiments mirrored the change in magnetic properties of the irradiated samples.
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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.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Vv High coercivity materials
68.65.Ac Multilayers
61.80.Jh Ion radiation effects

Giant magnetocaloric effect in ε-(Mn0.83Fe0.17)3.25Ge antiferromagnet

J. Du, W. B. Cui, Q. Zhang, S. Ma, D. K. Xiong, and Z. D. Zhang

Appl. Phys. Lett. 90, 042510 (2007); http://dx.doi.org/10.1063/1.2432274 (3 pages) | Cited 22 times

Online Publication Date: 26 January 2007

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The magnetic phase transition and magnetocaloric effect are investigated on ε-(Mn0.83Fe0.17)3.25Ge compound. A large positive magnetic entropy change ΔSM is observed, which is accompanied with a field-induced metamagnetic transition from a collinear to a triangular antiferromagnetic configuration in this antiferromagnetic compound. The maximum value of ΔSM is 11.6 J/kg K at 93 K for a magnetic field change of 7 T. The study on systems with antiferromagnetic phases may open an important field in searching new materials for magnetic refrigeration.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Gw Magnetic anisotropy
75.50.Ee Antiferromagnetics
65.40.G- Other thermodynamical quantities

Magnetic studies of GaN nanoceramics

A. J. Zaleski, M. Nyk, and W. Strek

Appl. Phys. Lett. 90, 042511 (2007); http://dx.doi.org/10.1063/1.2432275 (3 pages) | Cited 2 times

Online Publication Date: 26 January 2007

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The synthesis, morphology, and magnetization measurements of GaN nanoceramics obtained under high pressure are reported. In particular, the effect of grain size on magnetic properties of GaN nanopowders and nanoceramics was investigated. It was found that for the GaN nanoceramic characterized by the stronger deformation of nanocrystalline grains, the diamagnetic signal changes with external magnetic field similarly to the Meissner effect in superconductors.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.20.Ck Nonmetals
81.05.Ea III-V semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
62.25.-g Mechanical properties of nanoscale systems
81.40.Lm Deformation, plasticity, and creep

Self-generated in-plane superlattice in relaxed epitaxial La0.67Sr0.33MnO3 films

T. F. Zhou, G. Li, X. G. Li, S. W. Jin, and W. B. Wu

Appl. Phys. Lett. 90, 042512 (2007); http://dx.doi.org/10.1063/1.2432292 (3 pages) | Cited 5 times

Online Publication Date: 26 January 2007

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The strain relaxation and its effect on the in-plane superlattice formation of epitaxial La0.67Sr0.33MnO3 (LSMO) thin films on the (LaAlO3)0.3(Sr2AlTaO6)0.7 (001) [LSAT (001)] substrates were investigated as a function of film thickness by x-ray diffraction. Rocking curves and reciprocal space mappings around (002) and (103) reflections reveal that the film with a thickness above 27 nm is almost fully relaxed and has a modulated superlattice structure. The recovery of the pseudocubic angle of LSMO resulting from the relaxation of the shear strain introduced by the growth of rhombohedral LSMO on cubic LSAT was suggested to be the origin of the superlattice structure.
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68.65.Cd Superlattices
68.55.-a Thin film structure and morphology
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