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11 Apr 2005

Volume 86, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 86, 152101 (2005); http://dx.doi.org/10.1063/1.1897831 (3 pages)

Walid Hafez and Milton Feng
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Control of the vortex movement and arrangement by out-of-plane magnetic structures in twinned YBa2Cu3O7−x/La0.67Sr0.33MnO3 bilayer

F. Laviano, L. Gozzelino, E. Mezzetti, P. Przyslupski, A. Tsarev, and A. Wisniewski

Appl. Phys. Lett. 86, 152501 (2005); http://dx.doi.org/10.1063/1.1900307 (3 pages) | Cited 13 times

Online Publication Date: 4 April 2005

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In this article, we consider the magnetic interaction exerted on vortices in a thin YBa2Cu3O7−x film by a La0.67Sr0.33MnO3 layer. The magnetic coupling of the bilayer system was studied and locally imaged by means of magneto-optics. Twin boundaries in the LaAlO3 substrate cause a clear splitting of the manganite magnetic domains with well-defined in-plane magnetization separated by pinned out-of-plane magnetic structures. The vortices nucleated by the external magnetic field interact with the out-of-plane magnetic moments depending on their local structure and magnetic polarization. Different blocking mechanisms (sink or reservoir) are found for the vortex motion perpendicular to twin boundaries, whereas for vortices moving parallel to the out-of-plane magnetic structures either blocking or channelling effect is observed.
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74.72.-h Cuprate superconductors
75.50.Dd Nonmetallic ferromagnetic materials
74.78.-w Superconducting films and low-dimensional structures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films
74.25.Op Mixed states, critical fields, and surface sheaths
74.10.+v Occurrence, potential candidates
61.72.Mm Grain and twin boundaries
75.70.Kw Domain structure (including magnetic bubbles and vortices)
78.20.Ls Magneto-optical effects
75.60.Ch Domain walls and domain structure
75.30.Cr Saturation moments and magnetic susceptibilities
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Et Exchange and superexchange interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
74.25.Ha Magnetic properties including vortex structures and related phenomena
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Enhanced superconducting properties of Cu1-xTlxBa2Ca2-yMgyCu3O10-δ (y = 0, 0.5, 1.0, and 1.5)

Nawazish A. Khan and A. A. Khurram

Appl. Phys. Lett. 86, 152502 (2005); http://dx.doi.org/10.1063/1.1899254 (3 pages) | Cited 15 times

Online Publication Date: 4 April 2005

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In the present studies, the interplane couplings in Cu0.5Tl0.5Ba2Ca2Cu3O10-δ superconductor have been enhanced by Mg doping. With the improved interplane coupling a- and c-axis lengths are decreased while critical current density [Jc(H = 0)] is enhanced by two orders of magnitude and the zero resistivity critical temperature [Tc(R = 0)] is increased by 10 K. Predominant single phase of Cu1-xTlxBa2Ca2-yMgyCu3O10-δ (y = 0, 0.5, 1.0, and 1.5) was prepared by the solid state reaction of Ba(NO3)2, Ca(NO3)2, MgO, and Cu(CN). The material was checked by x-ray diffraction for crystallinity and was found to be the predominant single phase of Cu1-xTlxBa2Ca2-yMgyCu3O10-δ (y = 0, 0.5, 1.0, and 1.5) with a- and c-axes lengths 3.840 and 14.20 Å, respectively. The c-axis length decreases with the increased concentration of Mg in the compound. Fourier transform infrared absorption measurements have shown softening of apical oxygen modes with increased Mg doping and improved interplane coupling.
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74.72.-h Cuprate superconductors
74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)
74.25.F- Transport properties
74.25.Sv Critical currents
74.25.Kc Phonons
74.62.Dh Effects of crystal defects, doping and substitution
78.30.Hv Other nonmetallic inorganics
61.72.S- Impurities in crystals

Magnetic domain walls in T-shaped permalloy microstructures

T. Haug, C. H. Back, J. Raabe, S. Heun, and A. Locatelli

Appl. Phys. Lett. 86, 152503 (2005); http://dx.doi.org/10.1063/1.1897059 (3 pages) | Cited 3 times

Online Publication Date: 4 April 2005

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The magnetic domain wall width of T-shaped permalloy structures has been measured using a photoemission electron microscope and x-ray magnetic dichroism. The results are compared to micromagnetic simulations. The shape of the structures allows us to analyze 90° Néel walls. We find a decrease in domain wall width with decreasing contact dimensions as expected by theory and in good agreement with our micromagnetic simulations.
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75.50.Bb Fe and its alloys
75.60.Ch Domain walls and domain structure
75.40.Mg Numerical simulation studies
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.20.Ls Magneto-optical effects

Variable transformer for controllable flux coupling

M. G. Castellano, F. Chiarello, R. Leoni, D. Simeone, G. Torrioli, C. Cosmelli, and P. Carelli

Appl. Phys. Lett. 86, 152504 (2005); http://dx.doi.org/10.1063/1.1899746 (3 pages) | Cited 6 times

Online Publication Date: 4 April 2005

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We discuss and demonstrate a prototype of superconducting transformer with a flux transfer function that can be varied in a wide range, by acting on a control parameter. The device is realized by inserting a small hysteretic superconducting quantum interference device (dc-SQUID) with unshunted junctions, working as a Josephson junction with flux-controlled critical current, parallel to a superconducting transformer; by varying the magnetic flux coupled to the dc-SQUID, the transfer function for the flux coupled to the transformer can be varied. This feature can prove particularly appealing in the field of quantum computing, where it could be exploited to achieve a controllable magnetic coupling among flux-based qubits. Measurements carried out on a prototype at 4.2 K show a reduction factor of about 30 between the “on” and the “off” states. We discuss the system characteristics and the experimental results.
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85.25.Cp Josephson devices
85.25.Dq Superconducting quantum interference devices (SQUIDs)
85.25.Am Superconducting device characterization, design, and modeling
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents

Nanoengineered Curie temperature in laterally patterned ferromagnetic semiconductor heterostructures

K. F. Eid, B. L. Sheu, O. Maksimov, M. B. Stone, P. Schiffer, and N. Samarth

Appl. Phys. Lett. 86, 152505 (2005); http://dx.doi.org/10.1063/1.1900938 (3 pages) | Cited 11 times

Online Publication Date: 5 April 2005

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We demonstrate the manipulation of the Curie temperature of buried layers of the ferromagnetic semiconductor (Ga,Mn)As using nanolithography to enhance the effect of annealing. Patterning the GaAs-capped ferromagnetic layers into nanowires exposes free surfaces at the sidewalls of the patterned (Ga,Mn)As layers and thus allows the removal of Mn interstitials using annealing. This leads to an enhanced Curie temperature and reduced resistivity compared to unpatterned samples. For a fixed annealing time, the enhancement of the Curie temperature is larger for narrower nanowires.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
81.07.Bc Nanocrystalline materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
61.72.Cc Kinetics of defect formation and annealing
61.46.-w Structure of nanoscale materials
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
75.75.-c Magnetic properties of nanostructures
75.30.Gw Magnetic anisotropy
72.20.Fr Low-field transport and mobility; piezoresistance

Magnetization manipulation in (Ga,Mn)As by subpicosecond optical excitation

G. V. Astakhov, A. V. Kimel, G. M. Schott, A. A. Tsvetkov, A. Kirilyuk, D. R. Yakovlev, G. Karczewski, W. Ossau, G. Schmidt, L. W. Molenkamp, and Th. Rasing

Appl. Phys. Lett. 86, 152506 (2005); http://dx.doi.org/10.1063/1.1899231 (3 pages) | Cited 24 times

Online Publication Date: 5 April 2005

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We demonstrate complete reversal of a full magnetic hysteresis loop of the magnetic semiconductor (Ga,Mn)As by ultrashort optical excitation with a single subpicosecond light pulse, with obvious implications for ultrafast magneto-optical recording. Our approach utilizes the fourfold magnetic anisotropy of (Ga,Mn)As, in combination with the magnetic linear dichroism of the material.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.20.Ls Magneto-optical effects
61.82.Fk Semiconductors
78.47.-p Spectroscopy of solid state dynamics

Ferromagnetic percolation in MnxGe1−x dilute magnetic semiconductor

A. P. Li, J. Shen, J. R. Thompson, and H. H. Weitering

Appl. Phys. Lett. 86, 152507 (2005); http://dx.doi.org/10.1063/1.1899768 (3 pages) | Cited 72 times

Online Publication Date: 5 April 2005

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We have studied the magnetic and magnetotransport properties of Mn-doped Ge grown by molecular-beam epitaxy. This group-IV dilute ferromagnetic semiconductor exhibits two magnetic transitions. An upper critical temperature TC* ( ∼ 112 K for x ∼ 0.05) is evident from the extrapolated Curie–Weiss susceptibility and from the Arrott plot analysis of anomalous Hall effect data. The existence of a lower critical temperature TC ( ∼ 12 K for x ∼ 0.05) is established from ac susceptibility and magnetotransport data. The data are fully compatible with the existence of bound magnetic polarons or clusters below TC* which percolate at TC⪡TC*.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.20.Ck Nonmetals
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.Pq Other materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.S- Impurities in crystals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
75.30.Et Exchange and superexchange interactions
75.30.Cr Saturation moments and magnetic susceptibilities

Unlocking of remanent magnetization of pole heads by medium stray fields

H. J. Richter, D. C. Palmer, and E. Haftek

Appl. Phys. Lett. 86, 152508 (2005); http://dx.doi.org/10.1063/1.1899750 (3 pages) | Cited 4 times

Online Publication Date: 5 April 2005

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We report investigations of a stochastic phenomenon in which pole heads used for perpendicular recording stay magnetized after the driving current is switched off. This remanent magnetization causes erasure of the information previously written on the disk. The length of the erasure was found to be in the range of several μs up to a few ms. Surprisingly it is found that the remanent magnetization state can be reduced by magnetization patterns that already exist on the disk at the time of writing. Experimental evidence is presented which illustrates that the unlocking of the remanent state can be influenced by the type and location of these magnetization patterns. It is concluded that magnetization patterns creating rotating fields are most efficient in destroying these remanent states.
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75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Lr Magnetic aftereffects

Adjustable spin torque in magnetic tunnel junctions with two fixed layers

G. D. Fuchs, I. N. Krivorotov, P. M. Braganca, N. C. Emley, A. G. F. Garcia, D. C. Ralph, and R. A. Buhrman

Appl. Phys. Lett. 86, 152509 (2005); http://dx.doi.org/10.1063/1.1899764 (3 pages) | Cited 61 times

Online Publication Date: 6 April 2005

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We have fabricated nanoscale magnetic tunnel junctions (MTJs) with an additional fixed magnetic layer added above the magnetic free layer of a standard MTJ structure. This acts as a second source of spin-polarized electrons that, depending on the relative alignment of the two fixed layers, either augments or diminishes the net spin torque exerted on the free layer. The compound structure allows a quantitative comparison of spin torque from tunneling electrons and from electrons passing through metallic spacer layers, as well as analysis of Joule self-heating effects. This has significance for current-switched magnetic random access memory, where spin torque is exploited and, for magnetic sensing, where it is detrimental.
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75.75.-c Magnetic properties of nanostructures
72.25.−b
85.75.Dd Magnetic memory using magnetic tunnel junctions
85.75.Ss Magnetic field sensors using spin polarized transport

Fabrication and physical properties of Pb/Cu multilayered superconducting nanowires

François de Menten de Horne, Luc Piraux, and Sébastien Michotte

Appl. Phys. Lett. 86, 152510 (2005); http://dx.doi.org/10.1063/1.1900953 (3 pages) | Cited 6 times

Online Publication Date: 7 April 2005

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Using nanoporous media as templates for electrodeposition, we have fabricated multilayered Pb/Cu nanowires 50 nm in diameter and 20 μm long with Cu layer thicknesses as low as 10 nm. This was achieved by using a single-bath technique and a precise selection of the copper deposition potential to limit the redissolution of lead when the potential is raised to electrodeposit the more noble metal. Such superconductor∕normal multilayered nanowires show interesting magnetoresistance properties at a low magnetic field that may be related to the proximity effect, which can therefore be investigated in a quasi-one-dimensional geometry.
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84.71.Mn Superconducting wires, fibers, and tapes
81.07.Bc Nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
81.05.Bx Metals, semimetals, and alloys
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.Fk Multilayers, superlattices, heterostructures
74.25.F- Transport properties
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Pq Electrodeposition, electroplating
68.55.A- Nucleation and growth
68.65.Ac Multilayers
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.Np Metals and alloys

High-temperature ferromagnetism in pulsed-laser deposited epitaxial (Zn,Mn)O thin films: Effects of substrate temperature

A. K. Pradhan, Kai Zhang, S. Mohanty, J. B. Dadson, D. Hunter, Jun Zhang, D. J. Sellmyer, U. N. Roy, Y. Cui, A. Burger, S. Mathews, B. Joseph, B. R. Sekhar, and B. K. Roul

Appl. Phys. Lett. 86, 152511 (2005); http://dx.doi.org/10.1063/1.1897827 (3 pages) | Cited 32 times

Online Publication Date: 8 April 2005

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We report on the observation of remarkable room-temperature ferromagnetism in epitaxial (Zn,Mn)O films grown by a pulsed-laser deposition technique using high-density targets. The optimum growth conditions were demonstrated from x-ray measurements, microstructure, Rutherford backscattering, micro-Raman, and magnetic studies. Superior ferromagnetic properties were observed in (Zn,Mn)O films grown at a substrate temperature of 500 °C and with an oxygen partial pressure of 1 mTorr. Ferromagnetism becomes weaker with increasing substrate temperature due to the formation of isolated Mn clusters irrespective of higher crystalline quality of the film.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Fg Pulsed laser ablation deposition
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.A- Nucleation and growth
78.66.Li Other semiconductors
68.55.-a Thin film structure and morphology
78.30.Hv Other nonmetallic inorganics
81.05.Hd Other semiconductors
68.55.Nq Composition and phase identification
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Ultrafast magnetization dynamics of epitaxial Fe films on AlGaAs (001)

H. B. Zhao, D. Talbayev, Q. G. Yang, G. Lüpke, A. T. Hanbicki, C. H. Li, O. M. J. van ’t Erve, G. Kioseoglou, and B. T. Jonker

Appl. Phys. Lett. 86, 152512 (2005); http://dx.doi.org/10.1063/1.1900939 (3 pages) | Cited 13 times

Online Publication Date: 8 April 2005

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Uniform magnetization precessions are generated by ultrafast optical excitation along the in-plane easy axis [100], as well as along the hard axis [1-10], in epitaxial Fe films grown on AlGaAs (001) over a wide range of applied magnetic fields. From the temporal evolution of the coherent magnetization precession, we determine the magnetic anisotropy constants and damping parameters which are crucial in designing fast magnetic switching devices and spintronics devices.
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75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.47.-p Spectroscopy of solid state dynamics

Origin of the magnetic anisotropy induced by stress annealing in Fe-based nanocrystalline alloy

M. Ohnuma, K. Hono, T. Yanai, M. Nakano, H. Fukunaga, and Y. Yoshizawa

Appl. Phys. Lett. 86, 152513 (2005); http://dx.doi.org/10.1063/1.1901807 (3 pages) | Cited 15 times

Online Publication Date: 8 April 2005

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The dependence of the structural anisotropy of Fe-Si-B-Nb-Cu alloy on the applied stress during annealing has been studied by transmission x-ray diffraction. After crystallizing under stress, the Fe-Si nanocrystals show anisotropy in the lattice spacing of the (620) planes. Their elongations are proportional to the applied stress and show a linear correlation with the magnetic anisotropy energy, Ku. These results indicate that Ku originates from a magnetoelastic effect due to an elastic elongation of the Fe-Si phase constrained by the surrounding amorphous phase.
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75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.05.Bx Metals, semimetals, and alloys
81.07.Bc Nanocrystalline materials
75.30.Gw Magnetic anisotropy
75.80.+q Magnetomechanical effects, magnetostriction
75.75.-c Magnetic properties of nanostructures
81.40.Gh Other heat and thermomechanical treatments
61.46.-w Structure of nanoscale materials
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
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