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23 Mar 2009

Volume 94, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 94, 122502 (2009); http://dx.doi.org/10.1063/1.3100783 (3 pages)

Junhua Wang, Yisheng Shi, Juexian Cao, and Ruqian Wu
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Transmission electron microscopy study on the crystallization and boron distribution of CoFeB/MgO/CoFeB magnetic tunnel junctions with various capping layers

Toyoo Miyajima, Takahiro Ibusuki, Shinjiro Umehara, Masashige Sato, Shin Eguchi, Mineharu Tsukada, and Yuji Kataoka

Appl. Phys. Lett. 94, 122501 (2009); http://dx.doi.org/10.1063/1.3106624 (3 pages) | Cited 25 times

Online Publication Date: 23 March 2009

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High-resolution transmission electron microscopy and electron energy-loss spectroscopy (EELS) were used to study the microstructural properties of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) with various capping layers. Crystallization of CoFeB layers was strongly dependent on the capping materials, and was affected by B diffusion. With NiFe-cap MTJs, CoFeB crystallized from the cap interface and formed a fcc structure; on the other hand, with Ta- and Ti-cap MTJs, CoFeB crystallized from the MgO interface and formed a bcc structure. EELS analysis showed that B mainly diffused to the capping layers and rarely to the MgO layers with increasing temperature. With Ti-cap MTJs, B diffusion caused hcp-Ti crystals to form an amorphous structure and CoFeB crystallized at lower temperature.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.37.Og High-resolution transmission electron microscopy (HRTEM)
66.30.H- Self-diffusion and ionic conduction in nonmetals
64.70.K- Solid-solid transitions
79.20.Uv Electron energy loss spectroscopy
68.65.Ac Multilayers

Magnetization and magnetic anisotropy of metallophthalocyanine molecules from the first principles calculations

Junhua Wang, Yisheng Shi, Juexian Cao, and Ruqian Wu

Appl. Phys. Lett. 94, 122502 (2009); http://dx.doi.org/10.1063/1.3100783 (3 pages) | Cited 3 times

Online Publication Date: 23 March 2009

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Using the full potential linearized augmented plane wave method, we explored the magnetic anisotropy energies of metallophthalocyanine molecules with Mn, Fe, Co, and Ni. Their spin magnetic moments can be expressed as 8−nμB (n = 5,6,7,8 for Mn, Fe, Co, and Ni). Interestingly, Mn-phthalocyanine has a large orbital magnetic moment of 0.19μB and a sizable magnetic anisotropy energy of 2.72 meV useable for applications.
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75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Xx Molecular magnets

Epitaxial Mn2.5Ga thin films with giant perpendicular magnetic anisotropy for spintronic devices

Feng Wu, Shigemi Mizukami, Daisuke Watanabe, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, and Terunobu Miyazaki

Appl. Phys. Lett. 94, 122503 (2009); http://dx.doi.org/10.1063/1.3108085 (3 pages) | Cited 32 times

Online Publication Date: 24 March 2009

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We report on epitaxial growth and magnetic properties of Mn2.5Ga thin films, which were deposited on Cr/MgO single crystal substrates by magnetron sputtering. X-ray diffraction results revealed the epitaxial relationships as Mn2.5Ga(001)[100]∥Cr(001)[110]∥MgO(001)[100]. The presence of (002) and (011) superlattice peaks indicates that the films were crystallized into DO22 ordered structures. The perpendicular magnetic anisotropy (PMA) properties were found to be related to the extent of DO22 chemical ordering. A giant PMA (Kueff = 1.2×107 erg/cm3) and low saturation magnetization (Ms = 250 emu/cm3) can be obtained for the film with highest chemical ordering parameter (S = 0.8).
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75.70.Ak Magnetic properties of monolayers and thin films
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
81.15.Cd Deposition by sputtering
75.30.Gw Magnetic anisotropy

Half-metallicity and Gilbert damping constant in Co2FexMn1−xSi Heusler alloys depending on the film composition

Takahide Kubota, Sumito Tsunegi, Mikihiko Oogane, Shigemi Mizukami, Terunobu Miyazaki, Hiroshi Naganuma, and Yasuo Ando

Appl. Phys. Lett. 94, 122504 (2009); http://dx.doi.org/10.1063/1.3105982 (3 pages) | Cited 20 times

Online Publication Date: 24 March 2009

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Transport properties in magnetic tunnel junctions (MTJs) with Co2FexMn1−xSi (CFMS, x = 0–1.0)/Al–O/Co75Fe25 structure and Gilbert damping constant in the epitaxial CFMS films were investigated. The tunnel magnetoresistance ratio is as high as 75% in MTJs with x = 0.6 at room temperature. The Gilbert damping constant is minimal at x = 0.4. Relations between half-metallicity and the Gilbert damping constant in CFMS films were examined, revealing that the damping constant is small in half-metallic CFMS films.
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75.70.Ak Magnetic properties of monolayers and thin films
75.47.Np Metals and alloys
72.25.-b Spin polarized transport
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Magnetic semiconducting diode of p-Ge1−xMnx/n-Ge layers on silicon substrate

S. Majumdar, A. K. Das, and S. K. Ray

Appl. Phys. Lett. 94, 122505 (2009); http://dx.doi.org/10.1063/1.3097235 (3 pages) | Cited 5 times

Online Publication Date: 24 March 2009

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We have synthesized Ge-based magnetic diode composed of a Mn-doped Ge film grown on lightly As-doped Ge on silicon substrate. p-Ge1−xMnx/n-Ge heterostructure behaves like a conventional diode under forward and reverse biases and works like a spin valve below Curie temperature ( ∼ 50 K) under zero (B = 0) and nonzero (B = 300 mT) magnetic fields at forward bias (+2 V). A hysteretic behavior of p-n junction current with small coercive magnetic field implies the nonvolatility of the diode. Thus, a single element of p-Ge1−xMnx/n-Ge on silicon substrate deserves nonvolatility, rectification, and spin-valve-like functionality.
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85.30.Kk Junction diodes
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Enhancement of synchronized vortex lattice motion in hybrid magnetic/amorphous superconducting nanostructures

D. Perez de Lara, A. A. Alija, E. M. Gonzalez, J. I. Martin, M. Velez, J. M. Colino, J. V. Anguita, and J. L. Vicent

Appl. Phys. Lett. 94, 122506 (2009); http://dx.doi.org/10.1063/1.3103560 (3 pages) | Cited 1 time

Online Publication Date: 25 March 2009

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Superconducting a-Mo3Si and Nb films have been grown on arrays of Ni nanodots. We have studied the vortex lattice dynamics close to critical temperatures. Different vortex lattice configurations are obtained with the same array unit cell. These different vortex lattices occur at matching conditions between the vortex lattice and the array unit cell. The interplay between the random intrinsic pinning of the superconducting films and the periodic pinning of the array govern the vortex lattice configurations. Different vortex lattice configurations and enhancement of synchronized vortex lattice motion are obtained by increasing the periodic pinning strength and decreasing the random pinning strength.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Enhanced magnetic properties of FeCo ribbons nanocrystallized in magnetic field

P. Marín and A. Hernando

Appl. Phys. Lett. 94, 122507 (2009); http://dx.doi.org/10.1063/1.3091401 (3 pages) | Cited 7 times

Online Publication Date: 25 March 2009

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Tailoring the structure of nanocrystalline microstructures is an important step toward controlled design of novel nanostructured materials and devices. We demonstrate how the nanocrystalline microstructure of Co-rich ribbons can be tuned by annealing under magnetic field. The intensity of the field allows controlling different degrees of order at annealing temperatures corresponding to the first stages of the nanocrystallization process. The energy barrier for nucleation is directionally affected by the applied field. The influence of grains assembling on exchange coupling between grains has been analyzed by means of magnetic domains observation and magnetic characterization by means of a hysteresis loop.
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75.75.-c Magnetic properties of nanostructures
75.60.Nt Magnetic annealing and temperature-hysteresis effects
75.30.Et Exchange and superexchange interactions
75.60.Ch Domain walls and domain structure
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials

Reduction of the spin-torque critical current by partially canceling the free layer demagnetization field

Luqiao Liu, Takahiro Moriyama, D. C. Ralph, and R. A. Buhrman

Appl. Phys. Lett. 94, 122508 (2009); http://dx.doi.org/10.1063/1.3107262 (3 pages) | Cited 21 times

Online Publication Date: 26 March 2009

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We significantly reduce the critical current Ic0 for the onset of spin torque switching of the free layer in nanometer-scale in-plane magnetized spin valves by partially cancelling its intrinsic demagnetization field through the utilization of Co/Ni multilayer free layers. The out-of-plane magnetic anisotropy arising from the Co/Ni interfaces reduces the effective demagnetization field (Heff) while not significantly affecting the thermal stability of the free layer. A zero-thermal-fluctuation critical current density Jc0 ∼ 2×106 A/cm2 is determined through both current ramp rate and nanosecond pulse measurements, and comparisons with large Heff control samples confirm that this strategy is efficient in substantially decreasing Ic0.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.-d Domain effects, magnetization curves, and hysteresis
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy

Magnetization reversal dominated by domain wall pinning in FePt based spin valves

A. P. Mihai, J. P. Attané, L. Vila, C. Beigné, J. C. Pillet, and A. Marty

Appl. Phys. Lett. 94, 122509 (2009); http://dx.doi.org/10.1063/1.3106605 (3 pages) | Cited 6 times

Online Publication Date: 27 March 2009

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In this paper, we study FePt/NM/FePt//MgO (NM = Pt or Pd) spin valves with perpendicular magnetization deposited by molecular beam epitaxy. Using extraordinary Hall effect and magnetoresistance, we show that the electrodes can be of different coercivities and magnetically decoupled, with current-in-plane magnetoresistances up to 0.8% at room temperature. Finally, using magnetic force microscopy observations, we prove that the different coercivities of the electrodes are controlled by different magnetization reversals and domain-wall pinning, thus allowing the obtaining of an antiparallel state.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Np Metals and alloys
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
73.61.At Metal and metallic alloys
75.47.De Giant magnetoresistance
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.60.Jk Magnetization reversal mechanisms

Enhanced spin injection and detection in spin valves with integrated tunnel barriers

Andreas Vogel, Jeannette Wulfhorst, and Guido Meier

Appl. Phys. Lett. 94, 122510 (2009); http://dx.doi.org/10.1063/1.3109787 (3 pages) | Cited 13 times

Online Publication Date: 27 March 2009

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We study the spin-dependent transport in lateral spin-valve devices with aluminum oxide tunnel barriers at the interfaces between NiFe electrodes and an interconnecting Al strip. Different total conductivities per cross-sectional area are achieved by varying the oxygen pressure, the oxidation time, and the thickness of the oxidized aluminum layer. The experimental data are consistent with our theoretical description including spin diffusion, spin relaxation, and tunnel barriers at the interfaces between electrodes and aluminum strip. With decreasing tunnel conductance the amplitude of the nonlocal spin-valve effect increases by two orders of magnitude up to saturation.
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72.25.Hg Electrical injection of spin polarized carriers
72.25.Rb Spin relaxation and scattering
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Reduction in critical current of current induced switching in an inhomogeneous nanomagnet

M. C. Wu, A. Aziz, M. Ali, C. H. Marrows, B. J. Hickey, Z. H. Barber, and M. G. Blamire

Appl. Phys. Lett. 94, 122511 (2009); http://dx.doi.org/10.1063/1.3109790 (3 pages) | Cited 1 time

Online Publication Date: 27 March 2009

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We report low current-density switching of pseudospin valve nanopillars fabricated by a three-dimensional focused ion beam lithography. Simulations using the Landau–Liftshitz–Gilbert equation with Slonczewski spin transfer torque term demonstrate that magnetostatic coupling combined with an in-plane applied field results in a strongly inhomogeneous magnetization, which is close to the point of switching in both parallel and antiparallel configurations and so significantly reduced switching currents are possible.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
81.16.Nd Micro- and nanolithography
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
85.35.-p Nanoelectronic devices

Qubit dispersive readout scheme with a microstrip superconducting quantum interference device amplifier

S. Michotte

Appl. Phys. Lett. 94, 122512 (2009); http://dx.doi.org/10.1063/1.3109793 (3 pages) | Cited 2 times

Online Publication Date: 27 March 2009

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A flux qubit readout scheme involving a dispersive technique coupled to a microstrip superconducting quantum interference device (SQUID) amplifier has been tested experimentally. Thanks to the almost quantum limited noise of this amplifier at low temperature, this readout device is very promising for a design with actual qubits. Its proof of principle and low noise performance have been tested by simulating the qubit presence by applying a tiny flux change in the input SQUID. The resonant frequency of the amplifier is adjusted in situ with a varactor diode to approach the frequency of the tank circuit. Two operating modes (crossing or anticrossing regime) were identified.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
85.30.Kk Junction diodes
84.40.-x Radiowave and microwave (including millimeter wave) technology
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