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6 Feb 2012

Volume 100, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 061101 (2012); http://dx.doi.org/10.1063/1.3665180 (3 pages)

I. E. Khodasevych, C. M. Shah, S. Sriram, M. Bhaskaran, W. Withayachumnankul, B. S. Y. Ung, H. Lin, W. S. T. Rowe, D. Abbott, and A. Mitchell
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Broadband ferromagnetic resonance spectroscopy of permalloy triangular nanorings

J. Ding, M. Kostylev, and A. O. Adeyeye

Appl. Phys. Lett. 100, 062401 (2012); http://dx.doi.org/10.1063/1.3682083 (4 pages) | Cited 2 times

Online Publication Date: 7 February 2012

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We investigate the spin dynamics in triangular shaped permalloy rings using broadband ferromagnetic resonance spectroscopy. Compared with circular rings, we observed multiple resonance frequency peaks, which are strongly dependent on the orientation of the applied magnetic field relative to the horizontal edge of rings, displaying six-fold anisotropy. We validated our experimental results using modified Kittel equation [C. Kittel, Phys. Rev. 73, 155 (1948)] and dynamic micromagnetic simulations which show good agreement.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Ds Spin waves
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials

Dependence of negative differential resistance on electronic phase separation in unpatterned manganite films

J. F. Ding, K. X. Jin, Z. Zhang, and T. Wu

Appl. Phys. Lett. 100, 062402 (2012); http://dx.doi.org/10.1063/1.3684806 (4 pages) | Cited 1 time

Online Publication Date: 7 February 2012

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Here, we report that small but well-defined negative differential resistance (NDR) steps can be observed at critical voltages in unpatterned millimeter-scale manganite films of Pr0.65(Ca0.75Sr0.25)0.35MnO3. We systematically investigate the magneto-transport properties of strained thin films grown on LaAlO3 and SrTiO3 substrates and map out their phase diagrams which show temperature- and magnetic-field-dependent electronic phase separation (EPS). Our data suggest that the onset of NDR only occurs “deep” within the regions of EPS, underscoring the subtle nature of filamentary transport in manganite thin films with competing phases.
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72.20.My Galvanomagnetic and other magnetotransport effects
81.30.Dz Phase diagrams of other materials
75.70.Ak Magnetic properties of monolayers and thin films
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Anisotropic magneto-resistance in a GaMnAs-based single impurity tunnel diode: A tight binding approach

M. O. Nestoklon, O. Krebs, H. Jaffrès, S. Ruttala, J.-M. George, J.-M. Jancu, and P. Voisin

Appl. Phys. Lett. 100, 062403 (2012); http://dx.doi.org/10.1063/1.3683525 (3 pages)

Online Publication Date: 8 February 2012

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Using an advanced tight-binding approach, we estimate the anisotropy of the tunnel transmission associated with the rotation of the 5/2 spin of a single Mn atom forming an acceptor state in GaAs and located near an AlGaAs tunnel barrier. Significant anisotropies in both in-plane and out-of-plane geometries are found, resulting from the combination of the large spin-orbit coupling associated with the p-d exchange interaction, cubic anisotropy of heavy-hole dispersion and the low C2v symmetry of the chemical bonds.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Asymmetric switching behavior in perpendicularly magnetized spin-valve nanopillars due to the polarizer dipole field

D. B. Gopman, D. Bedau, S. Mangin, C. H. Lambert, E. E. Fullerton, J. A. Katine, and A. D. Kent

Appl. Phys. Lett. 100, 062404 (2012); http://dx.doi.org/10.1063/1.3681792 (3 pages) | Cited 5 times

Online Publication Date: 8 February 2012

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We report the free layer switching field distributions of spin-valve nanopillars with perpendicular magnetization. While the distributions are consistent with a thermal activation model, they show a strong asymmetry between the parallel to antiparallel and the reverse transition, with energy barriers more than 50% higher for the parallel to antiparallel transitions. The inhomogeneous dipolar field from the polarizer is demonstrated to be at the origin of this symmetry breaking. Interestingly, the symmetry is restored for devices with a lithographically defined notch pair removed from the midpoint of the pillar cross-section along the ellipse long axis. These results have important implications for the thermal stability of perpendicular magnetized magnetic random access memory bit cells.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.-c Magnetic properties of nanostructures

Exchange effects on spin-dependent ac transport

Jin Lan, Wen-Quan Sui, and Xuean Zhao

Appl. Phys. Lett. 100, 062405 (2012); http://dx.doi.org/10.1063/1.3682311 (3 pages) | Cited 1 time

Online Publication Date: 8 February 2012

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Spin-dependent ac transport problem is studied with exchange effects. Spin-spin exchange interaction and charge-charge Coulomb interaction are included simultaneously to determine the landscape of internal potential and the spin-dependent ac conductance. Gauge invariance and charge conservation are still satisfied. But spin current is not conserved. It is found that the exchange effects affect spin conductance dramatically, and hardly influence charge conductance. This shows the role of spin-accumulation in spin-dependent transport.
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72.25.Mk Spin transport through interfaces
75.30.Et Exchange and superexchange interactions
73.40.Rw Metal-insulator-metal structures

Electronic and magnetic properties of La2NiMnO6 and La2CoMnO6 with cationic ordering

Min Zhu, Yong Lin, Edward W. C. Lo, Qiong Wang, Zhengjie Zhao, and Wenhui Xie

Appl. Phys. Lett. 100, 062406 (2012); http://dx.doi.org/10.1063/1.3683550 (4 pages)

Online Publication Date: 10 February 2012

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Employing first‐principles electronic structure calculations, the electronic and magnetic properties of La2NiMnO6 and La2CoMnO6 with Ni/Mn and Co/Mn ordering in (001), (110), and (111) directions are investigated. The ground states of La2NiMnO6 and La2CoMnO6 are ferromagnetic semiconducting with alternative Ni/Mn and Co/Mn ordering along the (111) direction. Furthermore, it is found that La2NiMnO6 and La2CoMnO6 are half‐metal with Ni/Mn or Co/Mn ordering along (001) and (110) after considering the effect of electronic correlation. Our results would be helpful in exploring more spintronics materials.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
71.10.Hf Non-Fermi-liquid ground states, electron phase diagrams and phase transitions in model systems

Formation and structure of 360 and 540 degree domain walls in thin magnetic stripes

Youngman Jang, S. R. Bowden, Mark Mascaro, J. Unguris, and C. A. Ross

Appl. Phys. Lett. 100, 062407 (2012); http://dx.doi.org/10.1063/1.3681800 (4 pages) | Cited 3 times

Online Publication Date: 10 February 2012

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360°, 540°, and other complex transverse domain walls have been created in narrow cobalt wires connected to injection pads by cycling a magnetic field perpendicular to the wire length. The composite walls, formed by impingement of 180° transverse walls of alternating chirality, are stable over a wide field range. The structure of the walls observed at remanence by scanning electron microscopy with polarization analysis and by magnetic force microscopy is in good quantitative agreement with the prediction of micromagnetic simulations.
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75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Charge density waves condensate as measure of charge order and disorder in Eu1-xSrxMnO3 (x = 0.50, 0.58) manganites

Parul Pandey, Nilesh Awari, Rakesh Rana, Abhishek Singh, S. S. Prabhu, and D. S. Rana

Appl. Phys. Lett. 100, 062408 (2012); http://dx.doi.org/10.1063/1.3680094 (4 pages) | Cited 1 time

Online Publication Date: 10 February 2012

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We have explored the low-energy excitations in epitaxial thin films of Eu1-xSrxMnO3 [x = 0.50: spin-glass with short range charge-order and x = 0.58: long range charge-order] using terahertz time-domain spectroscopy. A finite frequency peak structure in optical conductivity is observed at ∼3.5 meV for both the films. While peak structure of x = 0.58 film possesses distinct properties of low-energy collective excitations of charge-density waves, the same is subtle and shallower with weaker peak conductivity for x = 0.50 film. These data, corroborated by magnetization, provide unambiguous evidence of the effect of range of charge-ordering, pinning, and disorder (induced by spin-glass state) on the manifestation of charge-density waves.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.78.-n Magnetization dynamics
75.10.Nr Spin-glass and other random models
75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

First-principles characterization of ferromagnetism in N-doped SrTiO3 and BaTiO3

Kesong Yang, Ying Dai, and Baibiao Huang

Appl. Phys. Lett. 100, 062409 (2012); http://dx.doi.org/10.1063/1.3684832 (3 pages) | Cited 5 times

Online Publication Date: 10 February 2012

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The spin-polarization and magnetic coupling character of N-doped SrTiO3 (STO) and BaTiO3 (BTO) are studied through first-principles calculations. The substitutional N doping at O sites leads to a half-metallic property and produces a magnetic moment of 1.0 μB. The magnetic interaction between the nearest and next-nearest N dopants results in a strong ferromagnetic (FM) coupling. When the distance between the N dopants is larger than 7 Å, the ground state of the system tends to be paramagnetic. A nitrogen-concentration threshold to produce the ferromagnetism is estimated. The calculated results give a good explanation for the experimentally observed ferromagnetism in N-doped STO and BTO.
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75.30.Cr Saturation moments and magnetic susceptibilities
61.72.up Other materials
72.25.-b Spin polarized transport
75.50.Dd Nonmetallic ferromagnetic materials
71.55.Ht Other nonmetals
75.20.Ck Nonmetals
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