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2 Oct 2006

Volume 89, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 89, 142101 (2006); http://dx.doi.org/10.1063/1.2358202 (3 pages)

H. C. Lin, P. D. Ye, Y. Xuan, G. Lu, A. Facchetti, and T. J. Marks
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Ferromagnetism in Mg-doped AlN from ab initio study

R. Q. Wu, G. W. Peng, L. Liu, Y. P. Feng, Z. G. Huang, and Q. Y. Wu

Appl. Phys. Lett. 89, 142501 (2006); http://dx.doi.org/10.1063/1.2358818 (3 pages) | Cited 38 times

Online Publication Date: 2 October 2006

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Ab initio calculations based on spin density functional theory were carried out to investigate Mg-doped AlN as a possible dilute magnetic semiconductor. It was found that both Al vacancy and substitutional Mg impurity in AlN lead to spin-polarized ground states. However, sufficient Al vacancy concentration may be difficult to achieve under thermal equilibrium because of the high formation energy of Al vacancy. On the other hand, formation energy of Mg defect is fairly low and the authors’ calculations predict a ferromagnetic coupling among MgN4 tetrahedra. Based on the analysis on Cu-doped ZnO [ L. H. Ye et al., Phys. Rev. B 73, 033203 (2006) ], room temperature ferromagnetism can be expected in AlN doped with 7% of Mg which can be incorporated at a growth temperature of 2000 K under N-rich condition.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.uj III-V and II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.J- Point defects and defect clusters
72.25.Dc Spin polarized transport in semiconductors

High critical current densities observed in PrBa2Cu3O7−δ/YBa2Cu3O7−δ/PrBa2Cu3O7−δ ultrathin film constrictions

Ch. Peroz, J. C. Villégier, A. F. Dégardin, B. Guillet, and A. J. Kreisler

Appl. Phys. Lett. 89, 142502 (2006); http://dx.doi.org/10.1063/1.2358320 (3 pages) | Cited 5 times

Online Publication Date: 2 October 2006

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An original process has been developed for fabricating 0.45×0.45 μm2 constrictions with normal metal banks using stacked YBa2Cu3O7−δ and PrBa2Cu3O7−δ ultrathin films. High values of critical temperature Tc ≈ 89 K and critical current densities Jc ≈ 2×107 A/cm2 at 77 K were measured on 17 nm thick YBa2Cu3O7−δ, after the complete fabrication on MgO substrate. The observed robust superconducting properties of the device under applied magnetic field are attributed to large edge barriers opposed to vortex entry inside the nanobridge section. As there is no apparent degradation of the superconducting properties after long time storage, the benefit of using ultrathin PrBa2Cu3O7−δ buffer and overlayer in YBa2Cu3O7−δ constrictions is confirmed. Such YBa2Cu3O7−δ nanowires are shown well adapted to phase-slip based devices and expected to fulfill the performances required in high frequency applications.
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74.25.Sv Critical currents
74.25.F- Transport properties
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Ha Magnetic properties including vortex structures and related phenomena
81.16.Rf Micro- and nanoscale pattern formation

Room-temperature ferrimagnetic semiconductor 0.6FeTiO3∙0.4Fe2O3 solid solution thin films

Hajime Hojo, Koji Fujita, Katsuhisa Tanaka, and Kazuyuki Hirao

Appl. Phys. Lett. 89, 142503 (2006); http://dx.doi.org/10.1063/1.2357547 (3 pages) | Cited 12 times

Online Publication Date: 3 October 2006

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The authors report on the fabrication of room-temperature ferrimagnetic semiconductor thin films composed of 0.6FeTiO3∙0.4Fe2O3 solid solution on α-Al2O3 (0001) substrates using a pulsed laser deposition method. A single ordered phase (Rmath symmetry) is obtained under very limited deposition conditions including oxygen partial pressure of 2.0×10−3 Pa and substrate temperature of 700 °C. The thin film with the ordered phase is an n-type semiconductor and ferrimagnetic with the Curie temperature >400 K. The Hall effect measurements at room temperature suggest that the carrier spins are polarized.
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81.15.Fg Pulsed laser ablation deposition
75.50.Gg Ferrimagnetics
75.50.Pp Magnetic semiconductors
68.55.A- Nucleation and growth
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Epitaxially grown MnAs/GaAs lateral spin valves

D. Saha, M. Holub, P. Bhattacharya, and Y. C. Liao

Appl. Phys. Lett. 89, 142504 (2006); http://dx.doi.org/10.1063/1.2358944 (3 pages) | Cited 27 times

Online Publication Date: 3 October 2006

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The authors report magnetoresistance of lateral spin valves fabricated from an epitaxially grown MnAs/GaAs heterostructure and utilizing a Schottky tunnel barrier for efficient spin injection. A coercive field difference between the two ferromagnetic MnAs contacts is obtained by a difference in aspect ratio. Peak magnetoresistances of 3.6% at 10 K and 1.1% at 125 K are measured for a 0.5 μm channel length spin valve. The authors observe an exponential decay of the peak magnetoresistance with increasing channel length, which is indicative of diffusive spin transport. The magnetoresistance increases with increasing bias and with decreasing temperature. Control experiments have been carried out to confirm the spin-valve effect.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.30.+y Surface double layers, Schottky barriers, and work functions
75.50.Dd Nonmetallic ferromagnetic materials

Carbohydrate doping to enhance electromagnetic properties of MgB2 superconductors

J. H. Kim, S. Zhou, M. S. A. Hossain, A. V. Pan, and S. X. Dou

Appl. Phys. Lett. 89, 142505 (2006); http://dx.doi.org/10.1063/1.2358947 (3 pages) | Cited 97 times

Online Publication Date: 3 October 2006

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The effect of carbohydrate doping on lattice parameters, microstructure, Tc, Jc, Hirr, and Hc2 of MgB2 has been studied. In this work the authors used malic acid as an example of carbohydrates as an additive to MgB2. The advantages of carbohydrate doping include homogeneous mixing of precursor powders, avoidance of expansive nanoadditives, production of highly reactive C, and significant enhancement in Jc, Hirr, and Hc2 of MgB2, compared to undoped samples. The Jc for MgB2+30 wt % C4H6O5 sample was increased by a factor of 21 at 5 K and 8 T without degradation of self-field Jc.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.62.Dh Effects of crystal defects, doping and substitution
74.25.Sv Critical currents
74.25.Op Mixed states, critical fields, and surface sheaths
61.66.Fn Inorganic compounds

One-step production of optimized Fe–Ga particles by spark erosion

J. I. Hong, V. C. Solomon, David J. Smith, F. T. Parker, E. M. Summers, and A. E. Berkowitz

Appl. Phys. Lett. 89, 142506 (2006); http://dx.doi.org/10.1063/1.2358825 (3 pages) | Cited 2 times

Online Publication Date: 4 October 2006

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Spherical Fe–Ga particles were prepared by spark erosion in liquid Ar, which directly incorporated the desirable rapid quench from high temperatures. The compositions of the particles investigated were 15.0, 16.3, and 18.9 at. % Ga, respectively, as determined from electron-probe microanalysis, x-ray diffraction, and Mössbauer spectra. Composites for magnetostriction measurements were prepared by mixing particles with epoxy at the volume fraction of 48% and curing in a magnetic field. Magnetostriction values of the composites were comparable to those of polycrystalline chill-cast alloys of the same compositions. Composites with particles having Ga concentrations of 18.9 at. % had the highest magnetostriction, similar to results reported for bulk Fe–Ga alloys.
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81.05.Qk Reinforced polymers and polymer-based composites
81.30.Fb Solidification
82.80.-d Chemical analysis and related physical methods of analysis
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
75.80.+q Magnetomechanical effects, magnetostriction
75.50.Tt Fine-particle systems; nanocrystalline materials

Atomic and electronic structure of the CoFeB/MgO interface from first principles

J. D. Burton, S. S. Jaswal, E. Y. Tsymbal, O. N. Mryasov, and O. G. Heinonen

Appl. Phys. Lett. 89, 142507 (2006); http://dx.doi.org/10.1063/1.2360189 (3 pages) | Cited 15 times

Online Publication Date: 5 October 2006

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First-principles calculations of the atomic and electronic structure of crystalline CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) are performed to understand the effect of B on spin-dependent transport in these junctions. The authors find that it is energetically favorable for B atoms to reside at the crystalline CoFeB/MgO interface rather than remain in the bulk of the crystalline CoFeB electrode. The presence of B at the interfaces is detrimental to tunneling magnetoresistance (TMR) because it significantly suppresses the majority-channel conductance through states of Δ1 symmetry. Preventing B segregation to the interfaces during annealing should result in an enhanced TMR in CoFeB/MgO/CoFeB MTJs.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
73.20.At Surface states, band structure, electron density of states
71.15.Nc Total energy and cohesive energy calculations
68.35.Ct Interface structure and roughness
75.50.Bb Fe and its alloys
81.40.Gh Other heat and thermomechanical treatments

Permalloy thin films exchange coupled to arrays of cobalt islands

A. Fraile Rodríguez, L. J. Heyderman, F. Nolting, A. Hoffmann, J. E. Pearson, L. M. Doeswijk, M. A. F. van den Boogaart, and J. Brugger

Appl. Phys. Lett. 89, 142508 (2006); http://dx.doi.org/10.1063/1.2357007 (3 pages) | Cited 6 times

Online Publication Date: 5 October 2006

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Periodic arrays of elongated cobalt islands exchange coupled to continuous Permalloy thin films were fabricated using silicon nitride stencil masks and the magnetic spin configurations during magnetization reversal were studied with photoemission electron microscopy. The presence of cobalt islands results in a spatial modulation of the magnetic properties of the Permalloy films and domain walls positioned at the island boundaries. While magneto-optical Kerr effect measurements indicate differences depending on film thickness, the direct observations reveal two reversal mechanisms: formation of domains running between the islands and coherent rotation followed by propagation of a large domain.
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75.50.Cc Other ferromagnetic metals and alloys
75.30.Et Exchange and superexchange interactions
68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms

High resolution determination of ferromagnetic metallic limit in epitaxial La1−xCaxMnO3 films on NdGaO3

D. Sánchez, L. E. Hueso, L. Granja, P. Levy, and N. D. Mathur

Appl. Phys. Lett. 89, 142509 (2006); http://dx.doi.org/10.1063/1.2360211 (3 pages) | Cited 8 times

Online Publication Date: 6 October 2006

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The physical properties of manganites depend strongly on sample morphology, probably due to strain. The authors investigate the influence of NdGaO3 substrates on the limit of the ferromagnetic-metallic phase field in La1−xCaxMnO3, doping with x = 1% resolution. Films with x = 0.40 show a metal-insulator transition, but the ferromagnetic volume fraction is half the spin aligned value. Films with x = 0.41 are similar but the metal-insulator transition is not always seen. Films with 0.42 ⩽ x ⩽ 0.45 are insulating, and the magnetization is dramatically reduced. The observed phase boundary indicates where to search for enhanced phase separation effects that may be exploited in thin films and devices.
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75.50.Dd Nonmetallic ferromagnetic materials
68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.61.Ng Insulators
61.72.up Other materials

Low-frequency nonlinear magnetoelectric effects in a ferrite-piezoelectric multilayer

K. E. Kamentsev, Y. K. Fetisov, and G. Srinivasan

Appl. Phys. Lett. 89, 142510 (2006); http://dx.doi.org/10.1063/1.2360239 (3 pages) | Cited 8 times

Online Publication Date: 6 October 2006

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Nonlinear magnetoelectric (ME) effects have been investigated in a multilayer of nickel zinc ferrite and lead zirconate titanate. The ME voltage has been measured under ac magnetic field amplitudes H of up to 1 kOe over the frequency range f = 1 mHz–1 Hz. Frequency doubling is observed for the ME voltage V generated across the multilayer and Fourier analysis of V shows harmonics of f. As H is increased or f is decreased, the shape of V is distorted and its magnitude decreases due to nonlinearity of the magnetostriction and the sample conductivity.
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75.80.+q Magnetomechanical effects, magnetostriction
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
77.65.-j Piezoelectricity and electromechanical effects

Confined Brownian motion of individual magnetic nanoparticles on a chip: Characterization of magnetic susceptibility

Kim van Ommering, Jeroen H. Nieuwenhuis, Leo J. van IJzendoorn, Bert Koopmans, and Menno W. J. Prins

Appl. Phys. Lett. 89, 142511 (2006); http://dx.doi.org/10.1063/1.2360246 (3 pages) | Cited 11 times

Online Publication Date: 6 October 2006

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An increasing number of biomedical applications requires detailed knowledge of the magnetic susceptibility of individual particles. With conventional techniques it is very difficult to analyze individual particles smaller than 1 μm. The authors demonstrate how the susceptibility of individual nanoparticles can be determined in an efficient way by optically analyzing the confined Brownian motion of a nanoparticle trapped in a known magnetic potential well on a chip. A setup is introduced that has a controllable two-dimensional magnetic potential well, which is defined by an integrated microscopic current wire. Susceptibility measurements have been performed on 150–450 nm superparamagnetic beads. They found differences in bead susceptibility of an order of magnitude and differences in volumetric susceptibility of more than a factor of 2.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Cr Saturation moments and magnetic susceptibilities

Metastable, epitaxial PrCo7 films with high energy product

A. K. Patra, V. Neu, S. Fähler, R. Groetzschel, and L. Schultz

Appl. Phys. Lett. 89, 142512 (2006); http://dx.doi.org/10.1063/1.2361195 (3 pages) | Cited 6 times

Online Publication Date: 6 October 2006

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Epitaxial Pr–Co films with a nominal composition of Pr2Co17 have been prepared on a Cr buffered MgO (110) substrate. Pole figures and magnetic measurements reveal that these Pr–Co films crystallize in a metastable disordered hexagonal PrCo7 phase (TbCu7 type) rather than an ordered rhombohedral Pr2Co17 phase (Th2Zn17 type). Consequently high uniaxial anisotropy at room temperature is observed instead of the planar anisotropy expected for the rhombohedral phase. The energy density obtained in the nonequilibrium Pr–Co films is (BH)max = 277 kJ/m3, which exceeds the (BH)max values of single phase Sm–Co films and Sm–Co/Fe and Pr–Co/Co multilayers.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
75.50.Ww Permanent magnets
75.30.Gw Magnetic anisotropy

Center of mass method for exchange bias measurements

Ondrej Hovorka, Andreas Berger, and Gary Friedman

Appl. Phys. Lett. 89, 142513 (2006); http://dx.doi.org/10.1063/1.2359431 (3 pages) | Cited 5 times

Online Publication Date: 6 October 2006

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Exchange bias measurement techniques are tested using an Ising model for exchange-coupled bilayer structures. In the presence of hysteresis loop asymmetry, the conventional exchange bias characterization method of measuring the sum of the coercive fields is found to be rather inaccurate if compared to the interface coupling energy. An alternative method based on the analysis of entire hysteresis loops is proposed, tested, and found to be substantially more robust.
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07.55.-w Magnetic instruments and components
75.30.Et Exchange and superexchange interactions
75.10.Hk Classical spin models
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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