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7 Jan 2008

Volume 92, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 92, 011101 (2008); http://dx.doi.org/10.1063/1.2828458 (3 pages)

F. Pedaci, S. Barland, E. Caboche, P. Genevet, M. Giudici, J. R. Tredicce, T. Ackemann, A. J. Scroggie, W. J. Firth, G.-L. Oppo, G. Tissoni, and R. Jäger
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Interface properties of Pb/InAs planar structures for Andreev spectroscopy

F. Magnus, K. A. Yates, S. K. Clowes, Y. Miyoshi, Y. Bugoslavsky, L. F. Cohen, A. Aziz, G. Burnell, M. G. Blamire, and P. W. Josephs-Franks

Appl. Phys. Lett. 92, 012501 (2008); http://dx.doi.org/10.1063/1.2828979 (3 pages)

Online Publication Date: 2 January 2008

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For Andreev spectroscopy to be a useful tool to detect spin accumulation in semiconductors, we show by simulation that there is a maximum value for the interface scattering parameter that can be tolerated. Three different fabrication routes for Pb/InAs planar junctions are explored and we find that the “etch-back” processing strategy is the most promising. Using the parameters extracted from the spectroscopic analysis, we find that the interface properties fall into four different regimes of behavior.
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73.40.Ns Metal-nonmetal contacts
72.25.-b Spin polarized transport

Observation of large low field magnetoresistance and large magnetocaloric effects in polycrystalline Pr0.65(Ca0.7Sr0.3)0.35MnO3

Anis Biswas, Tapas Samanta, S. Banerjee, and I. Das

Appl. Phys. Lett. 92, 012502 (2008); http://dx.doi.org/10.1063/1.2828980 (3 pages) | Cited 16 times

Online Publication Date: 2 January 2008

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Magnetotransport and magnetocaloric properties of polycrystalline Pr0.65(Ca0.7Sr0.3)MnO3 have been studied. Large low field magnetoresistance ( ∼ 100% at 75 K for 1 T field) with high magnetic field sensitivity ( ∼ 5000% T−1) has been observed due to the melting of charge ordered state. The system also shows large magnetocaloric effect at ∼ 215 and 90 K. The magnetic entropy change is ∼ 8 and 5.5 J/kg K, respectively, around these temperatures for a field change from 0 to 7 T. Such huge low field magnetoresistance along with large magnetocaloric effect exhibited by the material is interesting from the application point of view.
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75.47.Lx Magnetic oxides
75.30.Sg Magnetocaloric effect, magnetic cooling

Controllable switching of vortex chirality in magnetic nanodisks by a field pulse

Yuri Gaididei, Denis D. Sheka, and Franz G. Mertens

Appl. Phys. Lett. 92, 012503 (2008); http://dx.doi.org/10.1063/1.2829795 (3 pages) | Cited 13 times

Online Publication Date: 3 January 2008

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We propose a way of fast switching the chirality in a magnetic nanodisk by applying a field pulse. To break the symmetry with respect to clockwise or counterclockwise chirality, a mask is added by which an inhomogeneous field influences the vortex state of a nanodisk. Using numerical spin-lattice simulations, we demonstrate that chirality can be controllably switched by a field pulse, whose intensity is above some critical value. A mathematical definition for the chirality of an arbitrary shaped particle is proposed.
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75.60.-d Domain effects, magnetization curves, and hysteresis

Hysteretic ac loss of polygonally arranged superconducting strips carrying ac transport current

Yasunori Mawatari and Kazuhiro Kajikawa

Appl. Phys. Lett. 92, 012504 (2008); http://dx.doi.org/10.1063/1.2829793 (3 pages) | Cited 11 times

Online Publication Date: 3 January 2008

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The hysteretic ac loss of a current-carrying conductor in which multiple superconducting strips are polygonally arranged around a cylindrical former is theoretically investigated as a model of superconducting cables. Using the critical state model, we analytically derive the ac loss Qn of a total of n strips. The normalized loss Qn/Q1 is determined by the number of strips n and the ratio of the strip width 2w to the diameter 2R of the cylindrical former. When n⪢1 and w/R⪡1, the behavior of Qn is similar to that of an infinite array of coplanar strips.
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74.25.N- Response to electromagnetic fields
74.25.Sv Critical currents
84.71.Mn Superconducting wires, fibers, and tapes
84.71.Fk Superconducting cables

Current-excited magnetization reversal under in-plane magnetic field in a nanoscaled ferromagnetic wire

Yoshihiko Togawa, Takashi Kimura, Ken Harada, Tsuyoshi Matsuda, Akira Tonomura, Yoshichika Otani, and Tetsuya Akashi

Appl. Phys. Lett. 92, 012505 (2008); http://dx.doi.org/10.1063/1.2828865 (3 pages) | Cited 12 times

Online Publication Date: 4 January 2008

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We microscopically demonstrate that the magnetic domain is controllably nucleated and erased in the uniformly magnetized wire using a current pulse in small magnetic fields. Lorentz microscopy is performed in Permalloy nanowires with in-plane anisotropy. The stochastic nature of the magnetization reversal due to spin wave and thermal excitations in the absence of magnetic field completely disappears and turns into deterministic in the presence of small magnetic field, which enables the magnetization reversal control. We interpret that the phenomena are associated with Zeeman energy stabilization.
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75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
75.30.Ds Spin waves
75.50.Cc Other ferromagnetic metals and alloys
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Microstructural origin of switching field distribution in patterned Co/Pd multilayer nanodots

J. W. Lau, R. D. McMichael, S. H. Chung, J. O. Rantschler, V. Parekh, and D. Litvinov

Appl. Phys. Lett. 92, 012506 (2008); http://dx.doi.org/10.1063/1.2822439 (3 pages) | Cited 34 times

Online Publication Date: 4 January 2008

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We have identified an important microstructural origin of the switching field distribution (SFD) in patterned Co/Pd multilayer nanodots. In this study, we patterned a marked array of 115 nm Co/Pd nanodots on 50-nm-thick Si3N4 substrate. We identified the dots with unusually small and large (>2 standard deviations of the mean) switching fields with magnetic force microscopy, followed by microstructural characterization of the same dots with transmission electron microscopy (TEM). From electron diffraction, we found that most nanodots with small switching fields have strong (200) spots, whereas those with large switching fields lack these spots. While bright-field TEM images reveal an average grain size of 7 nm, dark-field images of the (200) spots reveal on average, a single grain of >10 nm in lateral dimensions. Since we observed a direct correlation between strong (200) reflections and small reversal fields, we conclude that the largest grain in each nanodot, with an in-plane [001] is the likely cause for premature switching, which in turn defines the SFD of this array.
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81.07.Ta Quantum dots
75.75.-c Magnetic properties of nanostructures
68.37.Rt Magnetic force microscopy (MFM)

Spin-torque driven ferromagnetic resonance of Co/Ni synthetic layers in spin valves

W. Chen, J.-M. L. Beaujour, G. de Loubens, A. D. Kent, and J. Z. Sun

Appl. Phys. Lett. 92, 012507 (2008); http://dx.doi.org/10.1063/1.2827570 (3 pages) | Cited 14 times

Online Publication Date: 4 January 2008

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Spin-torque driven ferromagnetic resonance (ST-FMR) is used to study thin Co/Ni synthetic layers with perpendicular anisotropy confined in spin valve based nanojunctions. Field swept ST-FMR measurements were conducted with a magnetic field applied perpendicular to the layer surface. The resonance lines were measured under low amplitude rf excitation, from 1 to 20 GHz. These results are compared with those obtained using conventional rf field driven FMR on extended films with the same Co/Ni layer structure. The layers confined in spin valves have a lower resonance field, a narrower resonance linewidth, and approximately the same linewidth vs frequency slope, implying the same damping parameter. The critical current for magnetic excitations is determined from measurements of the resonance linewidth vs dc current and is in accord with the one determined from I-V measurements.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy

Tuning in-plane magnetic anisotropy in (110) La2/3Ca1/3MnO3 films by anisotropic strain relaxation

I. C. Infante, J. O. Ossó, F. Sánchez, and J. Fontcuberta

Appl. Phys. Lett. 92, 012508 (2008); http://dx.doi.org/10.1063/1.2828701 (3 pages) | Cited 12 times

Online Publication Date: 7 January 2008

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We have investigated structural and functional properties of (110) La2/3Ca1/3MnO3 films grown on (110) SrTiO3 substrates. We have observed that there is an anisotropic in-plane lattice strain relaxation with faster relaxation along the [1−10] direction than along the [001] one, which leads to an anisotropic in-plane stress that evolves gradually with film thickness. The resultant anisotropy of the magnetoelastic energy imposes the [001] direction to be the in-plane magnetic easy axis and the strength of the in-plane magnetic anisotropy can be tuned by varying film thickness.
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75.30.Gw Magnetic anisotropy
75.80.+q Magnetomechanical effects, magnetostriction
68.60.Bs Mechanical and acoustical properties
68.55.jd Thickness

Magnetism of (Zn,Co)O thin films probed by x-ray absorption spectroscopies

K. Rode, R. Mattana, A. Anane, V. Cros, E. Jacquet, J.-P. Contour, F. Petroff, A. Fert, M.-A. Arrio, Ph. Sainctavit, P. Bencok, F. Wilhelm, N. B. Brookes, and A. Rogalev

Appl. Phys. Lett. 92, 012509 (2008); http://dx.doi.org/10.1063/1.2829610 (3 pages) | Cited 32 times

Online Publication Date: 7 January 2008

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We report on the electronic and magnetic properties of Co-doped ZnO thin films investigated by x-ray absorption spectroscopies and element selective magnetometry. For a low Co concentration (around 5%), we evidence a paramagnetic phase clearly correlated to Co2+ ions substituted to Zn in the ZnO matrix. For higher Co concentrations (around 25%), we demonstrate the coexistence of both paramagnetic and ferromagnetic phases. The use of advanced element and orbital selective techniques allows us through the distinct spectral signature of Co in ionic or metallic states to assign the ferromagnetic phase to the presence of Co in a metallic state as a consequence of Co metal clustering in our films.
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75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
78.70.Dm X-ray absorption spectra
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
61.72.U- Doping and impurity implantation

High frequency switching in bit-patterned media: A method to overcome synchronization issue

R. Sbiaa and S. N. Piramanayagam

Appl. Phys. Lett. 92, 012510 (2008); http://dx.doi.org/10.1063/1.2831692 (3 pages) | Cited 2 times

Online Publication Date: 7 January 2008

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In this study, we show that high frequency reversal of magnetization for over Tbits/in.2 recording density can be controlled by adjusting the magnetic field, media properties, and bit geometry. Using micromagnetic simulation, magnetization reversal speed depends strongly on exchange coupling (A) and the ratio between applied and anisotropy fields. The analysis also shows the effect of anisotropy variation and interbit interaction on magnetization switching. When high frequency write field is applied to less than a half bit, the switching may not occur for A higher than an optimal value. This characteristic can be used to reduce overwriting on adjacent bits.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.60.Jk Magnetization reversal mechanisms
75.50.Ss Magnetic recording materials
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions

Magnetic field induced transition from weak to strong ferromagnetic coupling in NiFe/Au/Co/Au multilayers

F. Stobiecki, M. Urbaniak, B. Szymański, J. Dubowik, P. Kuświk, M. Schmidt, T. Weis, D. Engel, D. Lengemann, A. Ehresmann, I. Sveklo, and A. Maziewski

Appl. Phys. Lett. 92, 012511 (2008); http://dx.doi.org/10.1063/1.2831714 (3 pages) | Cited 7 times

Online Publication Date: 7 January 2008

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We report on a specific magnetostatic coupling in sputter deposited (Ni80Fe20/Au/Co/Au)10 multilayers of alternating in-plane and out-of-plane magnetic anisotropies. We demonstrate on the basis of complementary studies (magnetoresistance, conventional magnetometry, and element specific soft x-ray resonant magnetic scattering hysteresis measurements) that the magnetization reversal of the Ni–Fe layers is strongly influenced by a magnetostatic coupling originating from the out-of-plane stripe domain stray fields of the Co layers.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.30.Gw Magnetic anisotropy
75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Anomalous microwave heating effects in Ce-doped La0.7Sr0.3MnO3: Possible role of grain boundary capacitative effects across cerium solubility limit

S. N. Kale, J. Mona, S. E. Lofland, S. D. Kulkarni, and S. B. Ogale

Appl. Phys. Lett. 92, 012512 (2008); http://dx.doi.org/10.1063/1.2827184 (3 pages) | Cited 2 times

Online Publication Date: 8 January 2008

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Ce-doped manganite bulk nanocompacts [La0.7−xCexSr0.3MnO3 (0<x<0.1)] are studied for their microwave heating properties at 2.45 GHz. The heating effect is found to be nonmonotonic as a function of cerium concentration, and anomalously large heating (burning) is observed for a small concentration window near x = 0.03. The x-ray diffraction studies show signatures of CeO2 phase in x>0.03 samples. The various characterizations collectively point to the key role of the developing grain boundary CeO2 layer which leads to highest capacitative intergrain-coupling and related charging-discharging effects when it is thinnest near the apparent Ce solubility limit of x~0.03.
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61.72.Mm Grain and twin boundaries
82.33.Vx Reactions in flames, combustion, and explosions
72.80.-r Conductivity of specific materials
81.07.Bc Nanocrystalline materials

Martensitic phase transformation in rapidly solidified Mn50Ni40In10 alloy ribbons

J. L. Sánchez Llamazares, T. Sanchez, J. D. Santos, M. J. Pérez, M. L. Sanchez, B. Hernando, Ll. Escoda, J. J. Suñol, and R. Varga

Appl. Phys. Lett. 92, 012513 (2008); http://dx.doi.org/10.1063/1.2827179 (3 pages) | Cited 28 times

Online Publication Date: 9 January 2008

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Heusler alloy Mn50Ni40In10 was produced as preferentially textured ribbon flakes by melt spinning, finding the existence of martensitic-austenic transformation with both phases exhibiting ferromagnetic ordering. A microcrystalline three-layered microstructure of ordered columnar grains grown perpendicularly to ribbon plane was formed between two thin layers of smaller grains. The characteristic temperatures of the martensitic transformation were MS = 213 K, Mf = 173 K, AS = 222 K, and Af = 243 K. Austenite phase shows a cubic L21 structure (a = 0.6013(3) nm at 298 K and a Curie point of 311 K), transforming into a modulated fourteen-layer modulation monoclinic martensite.
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81.30.Kf Martensitic transformations
81.30.Fb Solidification
75.50.Cc Other ferromagnetic metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.20.-n Methods of materials synthesis and materials processing

Ferromagnetism in pseudocubic BaFeO3 epitaxial films

C. Callender, D. P. Norton, R. Das, A. F. Hebard, and J. D. Budai

Appl. Phys. Lett. 92, 012514 (2008); http://dx.doi.org/10.1063/1.2832768 (3 pages) | Cited 8 times

Online Publication Date: 10 January 2008

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Growth and properties of epitaxial BaFeO3 thin films in the metastable cubic perovskite phase are examined. BaFeO3 films were grown on (012) LaAlO3 and (001) SrTiO3 single crystal substrates by pulsed-laser deposition. X-ray diffraction shows that films grown between 650 and 850 °C yield an oxygen-deficient BaFeO2.5+x pseudocubic perovskite phase that decreases in lattice spacing with increasing growth temperature. Magnetization measurements on as-deposited BaFeO3 films indicate weakly ferromagnetic behavior. Annealing in 1 atm oxygen ambient converts them into conductive and robustly ferromagnetic pseudocubic BaFeO3 phase with TC = 235 K. Observation of ferromagnetism with increasing oxygen content is consistent with superexchange coupling of Fe+4–O–Fe+4.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Fg Pulsed laser ablation deposition
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
68.55.A- Nucleation and growth

Effects of hydrostatic pressure on the magnetism and martensitic transition of Ni–Mn–In magnetic superelastic alloys

Lluís Mañosa, Xavier Moya, Antoni Planes, Oliver Gutfleisch, Julia Lyubina, Maria Barrio, Josep-Lluís Tamarit, Seda Aksoy, Thorsten Krenke, and Mehmet Acet

Appl. Phys. Lett. 92, 012515 (2008); http://dx.doi.org/10.1063/1.2830999 (3 pages) | Cited 30 times

Online Publication Date: 10 January 2008

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We report magnetization and differential thermal analysis measurements as a function of pressure across the martensitic transition in magnetically superelastic Ni–Mn–In alloys. It is found that the properties of the martensitic transformation are significantly affected by the application of pressure. All transition temperatures shift to higher values with increasing pressure. The largest rate of temperature shift with pressure has been found for Ni50Mn34In16 as a consequence of its small entropy change at the transition. Such a strong pressure dependence of the transition temperature opens up the possibility of inducing the martensitic transition by applying relatively low hydrostatic pressures.
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62.50.-p High-pressure effects in solids and liquids
81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
65.40.gd Entropy
81.40.Jj Elasticity and anelasticity, stress-strain relations

Vortex detection by electrical transport measurements on a single lead nanowire under axial magnetic field

S. Adam, F. de Menten de Horne, L. Piraux, and S. Michotte

Appl. Phys. Lett. 92, 012516 (2008); http://dx.doi.org/10.1063/1.2831657 (3 pages) | Cited 3 times

Online Publication Date: 10 January 2008

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Electrical transport measurements were performed on single electrodeposited superconducting lead nanowires (330 nm diameter) by applying a magnetic field parallel to the wire axis. We observe a vortex penetration while the nanowire is in the dissipative state generated by a phase-slip center. This results in a hysteresis in the resistance-current curves. A drop of the forward critical current leads to the disappearance of this hysteresis when the magnetic field is strong enough to stabilize the vortex at zero current. While the temperature is increased, lower magnetic fields are required to stabilize this vortex.
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74.25.Op Mixed states, critical fields, and surface sheaths
74.25.Sv Critical currents
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena

Laser activation of ferromagnetism in hydrogenated Ga1−xMnxAs

R. Farshchi, O. D. Dubon, D. J. Hwang, N. Misra, C. P. Grigoropoulos, and P. D. Ashby

Appl. Phys. Lett. 92, 012517 (2008); http://dx.doi.org/10.1063/1.2824833 (3 pages) | Cited 8 times

Online Publication Date: 11 January 2008

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We demonstrate the local depassivation of hydrogenated Ga1−xMnxAs by pulsed-laser annealing. The controlled removal of Mn–H defect complexes, which form upon hydrogenation and render Mn acceptors inactive, is achieved by focused laser irradiation. As a result, regions of electrically and ferromagnetically active Ga1−xMnxAs are formed within a nonactive, otherwise structurally identical film. The hydrogenated films subjected to blanket laser depassivation display a Curie temperature TC up to 60 K, or 60% of the TC of the as-grown films. These results demonstrate the direct laser writing of mesoscopic ferromagnetically active regions as a viable route for the realization of planar, nanoscale spintronic systems.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
73.61.Le Other inorganic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials
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