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23 Feb 2009

Volume 94, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 94, 082501 (2009); http://dx.doi.org/10.1063/1.3085971 (3 pages)

Chunghee Nam, B. G. Ng, F. J. Castaño, M. D. Mascaro, and C. A. Ross
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Current-driven vortex formation in a magnetic multilayer ring

Chunghee Nam, B. G. Ng, F. J. Castaño, M. D. Mascaro, and C. A. Ross

Appl. Phys. Lett. 94, 082501 (2009); http://dx.doi.org/10.1063/1.3085971 (3 pages) | Cited 10 times

Online Publication Date: 23 February 2009

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Current-driven domain wall (DW) motion has been studied in the NiFe layer of a Co/Cu/NiFe thin film ring using giant-magnetoresistance measurements in a four-point contact geometry. The NiFe layer is initially in an onion state configuration with two 180° DWs. An electric current drives the walls around the ring so that they annihilate and the NiFe layer forms a DW-free vortex state. The direction of motion of the two DWs is determined by the current polarity, enabling the vortex chirality to be selected.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Strong coupling of magnetic and dielectric properties in the a-axis-oriented orthorhombic HoMnO3 films

T. C. Han and J. G. Lin

Appl. Phys. Lett. 94, 082502 (2009); http://dx.doi.org/10.1063/1.3089361 (3 pages) | Cited 9 times

Online Publication Date: 24 February 2009

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High quality orthorhombic (OT) HoMnO3 (HMO) thin films with a-axis perpendicular to the film surface are grown on SrTiO3(110) substrates with the method of pulsed laser deposition. The structural, magnetic, and dielectric properties of OT-HMO films are measured. The temperature-dependent magnetization clearly displays an antiferromagnetic ordering near 44 K. Following, the lock-in transition from incommensurate to commensurate antiferromagnetic state is observed at 26 K with the applied field parallel to a-axis. At the same temperature, the dielectric constant rises abruptly, prevailing a strong coupling between the magnetic structure and the electric polarization as predicted for the E-phase multiferroic compounds.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
77.22.Ch Permittivity (dielectric function)
68.55.-a Thin film structure and morphology
64.70.Rh Commensurate-incommensurate transitions
77.55.-g Dielectric thin films

Enhanced exchange bias in sub-50-nm IrMn/CoFe nanostructure

M. Tofizur Rahman, Nazmun N. Shams, Ding Shuo Wang, and Chih-Huang Lai

Appl. Phys. Lett. 94, 082503 (2009); http://dx.doi.org/10.1063/1.3085965 (3 pages) | Cited 14 times

Online Publication Date: 25 February 2009

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The exchange bias field (Hex) of IrMn/CoFe deposited on a large-area nanoporous anodized alumina (AAO) is tailored by varying the pore density (D) and the network width (w) of AAO. The Hex increases with increasing D and reaches its maximum at D = 5.6×1010 cm−2 and w ∼ 28 nm. The enhancement in Hex, twice larger than that of the continuous film, is attributed to the reduction in antiferromagnetic (AFM) and ferromagnetic (FM) domain sizes. The suppression of Hex is observed for further increase in D, which may result from the excessive misalignment of AFM and FM spins and weakened AFM anisotropy.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys

Large converse magnetoelectric coupling in FeCoV/lead zinc niobate-lead titanate heterostructure

Yajie Chen, Jinsheng Gao, Trifon Fitchorov, Zhuhua Cai, K. S. Ziemer, Carmine Vittoria, and V. G. Harris

Appl. Phys. Lett. 94, 082504 (2009); http://dx.doi.org/10.1063/1.3086879 (3 pages) | Cited 15 times

Online Publication Date: 25 February 2009

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Multiferroic behavior was directly verified in a laminated ferroelectric-ferromagnetic heterostructure consisting of a FeCoV thick film (70 μm) and lead zinc niobate-lead titanate (PZN-PT) single crystal. This unique heterostructure demonstrates a significant converse magnetoelectric (CME) effect corresponding to a CME coupling constant of 31 Oe/kV cm−1. It derives from the soft magnetic and magnetostrictive properties (λ = 60 ppm) of FeCoV alloy and the superior electromechanical properties (d32 = −2800 pC/N) of PZN-PT crystal. The electric field controlled magnetic hysteresis is discussed in terms of a stress-induced anisotropy field model. The theoretical calculation is within 7% of the measured induced field of 240 Oe.
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75.80.+q Magnetomechanical effects, magnetostriction
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy

Study of weak ferromagnetism in polycrystalline multiferroic Eu doped bismuth ferrite

V. Raghavendra Reddy, Deepti Kothari, Ajay Gupta, and S. M. Gupta

Appl. Phys. Lett. 94, 082505 (2009); http://dx.doi.org/10.1063/1.3089577 (3 pages) | Cited 31 times

Online Publication Date: 25 February 2009

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Room temperature spontaneous magnetization and dielectric anomaly at Néel temperature are observed in 15% Eu doped bismuth ferrite indicating the multiferroic nature of the sample. With 15% Eu doping structural transformation from rhombohedral to triclinic is observed. Fe3+ and Eu3+ oxidation states are observed from 57Fe and 151Eu Mossbauer measurements, respectively. The high field 57Fe Mossbauer spectrum in longitudinal geometry shows an enhancement in the intensity of lines corresponding to Δm = 0 transitions, i.e., second and fifth lines in six line pattern. This observation suggests that the origin of spontaneous magnetization is due to weak ferromagnetism of Dzyaloshinskii–Moriya type.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
64.70.K- Solid-solid transitions
76.80.+y Mössbauer effect; other γ-ray spectroscopy

Effects of film thickness on manganite film-based heterjunctions

W. M. Lü, A. D. Wei, J. R. Sun, Y. Z. Chen, and B. G. Shen

Appl. Phys. Lett. 94, 082506 (2009); http://dx.doi.org/10.1063/1.3089698 (3 pages) | Cited 7 times

Online Publication Date: 25 February 2009

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Effects of film thickness on interfacial barrier have been studied for the La0.67Ca0.33MnO3/SrTiO3:Nb and La0.67Sr0.33MnO3/SrTiO3:Nb junctions. In addition to the evolution of the transport behavior from electron tunneling to thermionic emission, increase in film thickness from ∼ 5 to ∼ 50 nm causes a significant growth of interfacial barrier as revealed by photoresponse experiments, and the maximum change in interfacial barrier is ∼ 13% for La0.67Ca0.33MnO3/SrTiO3:Nb and ∼ 45% for La0.67Sr0.33MnO3/SrTiO3:Nb. A linear relation between interfacial barrier and lattice constant of the films is further found, which suggests the influence of lattice strains on interfacial barrier. Qualitative explanations are given.
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73.40.Gk Tunneling
68.55.aj Insulators
81.15.Fg Pulsed laser ablation deposition
79.40.+z Thermionic emission
73.40.Ns Metal-nonmetal contacts

Electrical spin injection from Fe into ZnSe(001)

A. T. Hanbicki, G. Kioseoglou, M. A. Holub, O. M. J. van ’t Erve, and B. T. Jonker

Appl. Phys. Lett. 94, 082507 (2009); http://dx.doi.org/10.1063/1.3089837 (3 pages) | Cited 1 time

Online Publication Date: 25 February 2009

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We have electrically injected spin-polarized current from ferromagnetic Fe(001) contacts into n-type ZnSe(001) using reverse-biased Schottky tunnel barriers which form at the Fe/ZnSe interface. Electrons transport through 3000 Å of n-ZnSe and radiatively recombine in GaAs, where the circular polarization of the electroluminescence provides a quantitative measure of spin polarization. We measure electron spin polarizations over 50% in the GaAs up to 100 K. Spin injection efficiencies achieved in Fe/ZnSe are comparable to those reported for Fe/AlGaAs or Fe/GaAs Schottky tunnel structures, consistent with the common band symmetries of the Fe majority band and the conduction band of the respective semiconductor.
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72.25.Dc Spin polarized transport in semiconductors
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
73.30.+y Surface double layers, Schottky barriers, and work functions
75.50.Bb Fe and its alloys
78.60.Fi Electroluminescence
73.20.At Surface states, band structure, electron density of states

Growth and superconductivity of FeSex crystals

U. Patel, J. Hua, S. H. Yu, S. Avci, Z. L. Xiao, H. Claus, J. Schlueter, V. V. Vlasko-Vlasov, U. Welp, and W. K. Kwok

Appl. Phys. Lett. 94, 082508 (2009); http://dx.doi.org/10.1063/1.3093838 (3 pages) | Cited 19 times

Online Publication Date: 25 February 2009

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Iron selenide (FeSex) crystals with lateral dimensions up to millimeters were grown via a vapor self-transport method. The crystals consist of the dominant α-phase with trace amounts of β-phase as identified by powder x-ray diffraction. With four-probe resistance measurements, we obtained a zero resistance critical temperature of 7.5 K and a superconducting onset transition temperature of up to 11.8 K in zero magnetic field as well as an anisotropy of 1.5±0.1 for the critical field. Magnetization measurements on individual crystals reveal the coexistence of superconductivity and ferromagnetism.
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81.10.Bk Growth from vapor
74.10.+v Occurrence, potential candidates
74.62.-c Transition temperature variations, phase diagrams
74.25.Op Mixed states, critical fields, and surface sheaths
75.30.Gw Magnetic anisotropy
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Imaging of variation in charge/orbital/spin ordering structure in Sm1−xSrxMnO3 (x = 0.55 and 0.6)

X. Z. Yu, Y. Tomioka, T. Asaka, K. Kimoto, T. Arima, Y. Tokura, and Y. Matsui

Appl. Phys. Lett. 94, 082509 (2009); http://dx.doi.org/10.1063/1.3086311 (3 pages) | Cited 6 times

Online Publication Date: 26 February 2009

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Imaging of charge/orbital ordering (CO/OO) structure and canted antiferromagnetic (AFM) domain structure in Sm1−xSrxMnO3 (x = 0.55 and 0.6) has successfully been demonstrated. In the x = 0.55 compound, the commensurate CO/OO structure with modulation vector Q = (0,1/3,0) was observed above the AFM transition temperature (TNA ∼ 180 K). This modulation structure changes to an incommensurate one below TNA. In the x = 0.6 compound, the typical 180° magnetic domains were observed in the (110) plane below 50 K indicating the canted AFM structure. This AFM structure locally collapses because of the existence of the short-range CO.
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75.60.Ch Domain walls and domain structure
75.50.Ee Antiferromagnetics
64.70.Rh Commensurate-incommensurate transitions
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
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