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25 Dec 2006

Volume 89, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 89, 263110 (2006); http://dx.doi.org/10.1063/1.2424541 (3 pages)

Ch. Deneke, U. Zschieschang, H. Klauk, and O. G. Schmidt
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Magnetostriction studies in an antiferromagnetic polycrystalline Mn42Fe58 alloy

W. Y. Peng and J. H. Zhang

Appl. Phys. Lett. 89, 262501 (2006); http://dx.doi.org/10.1063/1.2405850 (3 pages) | Cited 5 times

Online Publication Date: 26 December 2006

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Magnetostriction “jump” effect often occurs in ferromagnetic materials. However, in this letter, the jump effect is observed in antiferromagnetic face-centered-cubic austenitic polycrystalline Mn42Fe58 alloy at room temperature. The magnetostriction under an applied field of 1.0 T is 169 ppm parallel to the field. The jump magnetostriction of −581 ppm, which is antiparallel to the field, is obtained when the sample is subjected to the compressive stress of 1.52 MPa. The relation between the magnetostriction and the field strength is discussed.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Ee Antiferromagnetics
62.50.-p High-pressure effects in solids and liquids
81.40.Vw Pressure treatment

Enhancement of exchange coupling between GaMnAs and IrMn with self-organized Mn(Ga)As at the interface

H. T. Lin, Y. F. Chen, P. W. Huang, S. H. Wang, J. H. Huang, C. H. Lai, W. N. Lee, and T. S. Chin

Appl. Phys. Lett. 89, 262502 (2006); http://dx.doi.org/10.1063/1.2410234 (3 pages) | Cited 6 times

Online Publication Date: 26 December 2006

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An atomically flat and uniform reaction layer of Mn(Ga)As was found to self-organize at the (Ga,Mn)As/IrMn interface by postannealing. The Mn(Ga)As layer exhibits strong ferromagnetic characteristics up to the measured 300 K. In particular, the manifested horizontal shift of field-cooled hysteresis loops shows a clear signature of exchange bias attributable to the exchange coupling between IrMn and Mn(Ga)As. Implication from composition analyses, exchange-bias effect, and thickness dependence of the Mn(Ga)As layer versus annealing conditions is also discussed.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing

Structural and magnetic properties of epitaxial thin films of the ordered double perovskite La2CoMnO6

H. Z. Guo, A. Gupta, T. G. Calvarese, and M. A. Subramanian

Appl. Phys. Lett. 89, 262503 (2006); http://dx.doi.org/10.1063/1.2422878 (3 pages) | Cited 23 times

Online Publication Date: 26 December 2006

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Epitaxial thin films of the ordered ferromagnetic double perovskite La2CoMnO6 have been grown on (001)-oriented SrTiO3 substrates by pulsed laser deposition. X-ray photoemission spectroscopy analysis suggests that the Mn and Co ions are primarily in the 4+ and 2+ valence states. Magnetic measurements indicate the presence of two phases: a majority and a minority ferromagnetic phase with transition temperatures of 230 and 80 K, respectively. A spin-glass-type magnetic behavior is also indicated for the films based on time-dependent measurements. The spin-glass behavior likely arises from a competition between ferromagnetic and antiferromagnetic interactions because of local disorder, even in films grown under optimal conditions.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Lk Spin glasses and other random magnets
75.50.Ee Antiferromagnetics
81.15.Fg Pulsed laser ablation deposition

Vacancy induced structural and magnetic transition in MnCo1−xGe

Jian-Tao Wang, Ding-Sheng Wang, Changfeng Chen, O. Nashima, T. Kanomata, H. Mizuseki, and Y. Kawazoe

Appl. Phys. Lett. 89, 262504 (2006); http://dx.doi.org/10.1063/1.2424273 (3 pages) | Cited 13 times

Online Publication Date: 26 December 2006

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The authors report ab initio total energy calculations on the first-order structural transition of the ferromagnetic MnCo1−xGe(0.00 ⩽ x ⩽ 0.25) intermetallic compound. They show that increasing Co vacancies induce a transition from an orthorhombic structure at 0 ⩽ x ⩽ 0.08 to a hexagonal structure at x>0.08. A concomitant high-to-low moment magnetic transition and a large magnetovolume effect occur due to the change of the symmetry and the resulting coupling distance between the magnetic atoms. These results provide an excellent account for the experimental results and reveal the crucial role of the Co vacancies in determining the relative structural stability and the magnetic properties of MnCo1−xGe.
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64.70.K- Solid-solid transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.J- Point defects and defect clusters
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.50.Cc Other ferromagnetic metals and alloys

Prospects for detection of spin accumulation using submicron planar Andreev array spectroscopy

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

Appl. Phys. Lett. 89, 262505 (2006); http://dx.doi.org/10.1063/1.2424279 (3 pages) | Cited 4 times

Online Publication Date: 27 December 2006

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Andreev spectroscopy can be employed to measure transport spin polarization. Planar Andreev devices have an advantage over point-contact Andreev spectroscopy as they offer greater control over interface quality and the possibility of spatially resolved information about spin polarization using submicron Andreev junction arrays. The authors compare the performance of Pb point contacts onto Cu and Co with that of large area and submicron planar junctions and singularly connected nanoarrays. Planar structures compare favorably to point contacts although the fabrication method influences extracted parameters. The authors find that submicron planar junction reproducibility does not adversely affect the prospects for developing arrays for detection of spin accumulation.
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74.50.+r Tunneling phenomena; Josephson effects
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.F- Transport properties

Strain induced magnetic anisotropy in highly epitaxial CoFe2O4 thin films

W. Huang, J. Zhu, H. Z. Zeng, X. H. Wei, Y. Zhang, and Y. R. Li

Appl. Phys. Lett. 89, 262506 (2006); http://dx.doi.org/10.1063/1.2424444 (3 pages) | Cited 31 times

Online Publication Date: 27 December 2006

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Cobalt ferrite (CoFe2O4) thin films were epitaxially grown on (001) SrTiO3 and (001) MgO by laser molecular beam epitaxy. Microstructural studies indicate that the CoFe2O4 grown on (001) SrTiO3 with compressive strain are c-oriented island growth mode with rough surface morphology, whereas the films on (001) MgO with tensile strain become c oriented with layer-by-layer mode. Magnetic property studies reveal that the compressive strained CoFe2O4 films on (001) SrTiO3 can significantly enhance out-of-plane magnetization (190 emu/cm3) with a large coercivity (3.8 kOe). In contrast, the tensile strained CoFe2O4 films on (001) MgO exhibit weak magnetic anisotropy. These results suggest that strong magnetic anisotropy is highly dependent on the lattice mismatch induced strain.
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75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.60.Bs Mechanical and acoustical properties
68.35.B- Structure of clean surfaces (and surface reconstruction)

Dynamics of vortex core switching in ferromagnetic nanodisks

Q. F. Xiao, J. Rudge, B. C. Choi, Y. K. Hong, and G. Donohoe

Appl. Phys. Lett. 89, 262507 (2006); http://dx.doi.org/10.1063/1.2424673 (3 pages) | Cited 41 times

Online Publication Date: 28 December 2006

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Dynamics of magnetic vortex core switching in nanometer-scale Permalloy disk, having a single vortex ground state, was investigated by micromagnetic modeling. When an in-plane magnetic field pulse with an appropriate strength and duration is applied to the vortex structure, additional two vortices, i.e., a circular and an antivortex, are created near the original vortex core. Sequentially, the vortex-antivortex pair annihilates. A spin wave is created at the annihilation point and propagated through the entire element; the relaxed state for the system is the single vortex state with a switched vortex core.
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Ds Spin waves
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials

Improvement of magnetic properties of granular perpendicular recording media by using a fcc nonmagnetic intermediate layer with stacking faults

Atsushi Hashimoto, Shin Saito, Norikazu Itagaki, and Migaku Takahashi

Appl. Phys. Lett. 89, 262508 (2006); http://dx.doi.org/10.1063/1.2424280 (3 pages) | Cited 10 times

Online Publication Date: 28 December 2006

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Various binary systems are investigated as face-centered cubic (fcc) bases for the nonmagnetic intermediate layer (NMIL) in granular perpendicular recording media. Loss of stacking order on the (111) plane in fcc NMIL is found to enhance the perpendicular magnetic anisotropy energy (KuRL) of the overlying medium. One persuasive reason for this enhancement is the preferred epitaxial growth of magnetic grains on only the (111) atomic terrace of the fcc NMIL due to collapse of the sixfold symmetry of (math11), (1math1), and (11math) atomic terraces of the fcc NMIL.
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75.50.Ss Magnetic recording materials
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
61.72.Nn Stacking faults and other planar or extended defects

Trends in spin-transfer-driven magnetization dynamics of CoFe/AlO/Py and CoFe/MgO/Py magnetic tunnel junctions

G. Finocchio, G. Consolo, M. Carpentieri, A. Romeo, B. Azzerboni, L. Torres, and L. Lopez-Diaz

Appl. Phys. Lett. 89, 262509 (2006); http://dx.doi.org/10.1063/1.2425017 (3 pages) | Cited 16 times

Online Publication Date: 28 December 2006

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A spin-polarized current is able to excite magnetization dynamics in nanomagnets. A detailed theoretical study of dynamics in low and high field regimes in AlO and MgO magnetic tunnel junctions (MTJs) is presented, considering the maximum value of the applied current which comes from the breakdown voltage of the tunnel barrier. In low field regime, dynamics with a well-defined peak in frequency is observed. In high field regime, AlO MTJ presents the same behavior, while the magnetization in the MgO MTJ shows chaotic motion with a noisy spectrum. Lastly, an effect of the presence of a pinhole in the tunnel barrier is discussed.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.Mk Spin transport through interfaces
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Interfacial and quantum well effects on ac magnetotransport of La0.7Sr0.3MnO3/La1.4Sr1.6Mn2O7 composites

C. Y. Hsu, Hsiung Chou, B. Y. Liao, and J. C. A. Huang

Appl. Phys. Lett. 89, 262510 (2006); http://dx.doi.org/10.1063/1.2422880 (3 pages) | Cited 5 times

Online Publication Date: 29 December 2006

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The field-dependent complex impedance (CI) spectroscopy is employed to clarify the origins of ac magnetoimpedance (MI) effects at room temperature near the conduction threshold of [La0.67Sr0.33MnO3(113)]1−x/[La1.67Sr1.33Mn2O7(327)]x composites. The field-dependent CI spectra in 113-327 granular composites are further transformed to field-dependent magnetoconductance (MC) spectra. The frequency-dependent high-field and low-field MC spectra can be well interpreted by including the trap-state contributions in 113-327 interfaces and 327 grain boundaries, together with the leakage-region-induced spin-dependent quantum well state effect. The principle of this work could be applied to study the magnetoresistance and MI effects of magnetic granular composites.
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75.47.Lx Magnetic oxides
73.63.Hs Quantum wells
73.43.Qt Magnetoresistance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Mm Grain and twin boundaries

Observation of magnetism in the nanoscale amorphous ruthenium clusters prepared by ion beam mixing

W. C. Wang, Y. Kong, X. He, and B. X. Liu

Appl. Phys. Lett. 89, 262511 (2006); http://dx.doi.org/10.1063/1.2425037 (3 pages) | Cited 4 times

Online Publication Date: 29 December 2006

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A unique composite of nanoscale amorphous Ru clusters embedded in the amorphous Ru/Ta matrix was observed in the Ru/Ta multilayered films upon ion irradiation. It was found that the magnetic moment of the Ru nanoclusters varied with cluster size, i.e., when the diameter of the clusters changed from 1 to 5 nm, the magnetic moment decreased from 0.24μB (parallel) and 0.27μB (vertical) to 0μB and 0μB, respectively, according well with the prediction from ab initio calculations.
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75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Cr Saturation moments and magnetic susceptibilities
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
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