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2 Jul 2007

Volume 91, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 91, 013501 (2007); http://dx.doi.org/10.1063/1.2753120 (3 pages)

J. Verd, A. Uranga, G. Abadal, J. Teva, F. Torres, F. Pérez-Murano, J. Fraxedas, J. Esteve, and N. Barniol
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Where does the spin reside in ferromagnetic Cu-doped ZnO?

D. J. Keavney, D. B. Buchholz, Q. Ma, and R. P. H. Chang

Appl. Phys. Lett. 91, 012501 (2007); http://dx.doi.org/10.1063/1.2751587 (3 pages) | Cited 29 times

Online Publication Date: 2 July 2007

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The authors report a soft x-ray absorption spectroscopy and magnetic circular dichroism study of the ferromagnetism in pulsed-laser-deposited Cu-doped ZnO thin films, which display robust room-temperature ferromagnetic signatures using bulk magnetization probes. In this work, the authors probe the spin asymmetries in the Cu 3d, O 2p, and Zn 3d states individually. They find a paramagnetic component originating from the Cu 3d, and no magnetic signal in the O or Zn. They find no dichroic signal consistent with ferromagnetism originating from any of these states.
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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
78.20.Ls Magneto-optical effects
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Anomalous Hall effect in anatase Co:TiO2 ferromagnetic semiconductor

R. Ramaneti, J. C. Lodder, and R. Jansen

Appl. Phys. Lett. 91, 012502 (2007); http://dx.doi.org/10.1063/1.2751133 (3 pages) | Cited 21 times

Online Publication Date: 2 July 2007

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The observation of the anomalous Hall effect (AHE) in Co-doped TiO2 ferromagnetic semiconductor in the anatase phase is reported. An AHE is observed with magnetic hysteresis consistent with remanence and coercivity obtained from magnetometry data. The anatase films also have reasonable mobility ( ∼ 17 cm2/V s) at room temperature and carrier density of ∼ 5×1018 cm−3. The AHE in such films with relatively low carrier density gives prospects to test whether the ferromagnetism in this oxide semiconductor is carrier mediated using a field effect device configuration.
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75.50.Pp Magnetic semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
73.61.Le Other inorganic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.20.Fr Low-field transport and mobility; piezoresistance

Absence of long-range Ni/Mn ordering in ferromagnetic La2NiMnO6 thin films

M. P. Singh, C. Grygiel, W. C. Sheets, Ph. Boullay, M. Hervieu, W. Prellier, B. Mercey, Ch. Simon, and B. Raveau

Appl. Phys. Lett. 91, 012503 (2007); http://dx.doi.org/10.1063/1.2753715 (3 pages) | Cited 27 times

Online Publication Date: 2 July 2007

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Epitaxial La2NiMnO6 thin films have been grown on (001)-orientated SrTiO3 using the pulsed laser deposition technique. The thin film samples are semiconducting and ferromagnetic with a Curie temperature close to 270 K, a coercive field of 920 Oe, and a saturation magnetization of 4.85μB/formula unit. Transmission electron microscopy, conducted at room temperature, reveals a majority phase having an “I-centered” structure with a ≈ c ≈ asubmath and b ≈ 2asub along with minority phase domains having a “P-type” structure (asub being the lattice parameter of the cubic perovskite structure). A discussion on the absence of Ni/Mn long-range ordering, in light of recent literature on the ordered double-perovskite La2NiMnO6 is presented.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.55.-a Thin film structure and morphology

Enhanced grain surface effect on magnetic properties of La0.5Gd0.2Sr0.3MnO3 nanoparticles: A comparison with bulk counterpart

P. Dey, T. K. Nath, and A. Banerjee

Appl. Phys. Lett. 91, 012504 (2007); http://dx.doi.org/10.1063/1.2753547 (3 pages) | Cited 2 times

Online Publication Date: 2 July 2007

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Magnetization studies on La0.5Gd0.2Sr0.3MnO3 (LGSMO) nanoparticles ( ∼ 20 nm) reveal superparamagnetic phase associated with this system and thereby contrasting from cluster glass (CG) phase of its bulk counterpart. Doping of Gd on La sites and its antiferromagnetic coupling with Mn lattices are expected to induce random magnetic disorder in the magnetic lattice of LGSMO system. Study reveals that random magnetic disorder, which results in CG phase in an otherwise long range ordered ferromagnetic host matrix of bulk, does not have similar significant effect when the uniformity of the host matrix reduces to nanosize. On the contrary, analysis brings out that magnetic properties of LGSMO nanoparticles are primarily decided by its nanodimension having physical size of ∼ 20 nm, which yield single domain magnetic entities of dimension of ∼ 12 nm surrounded by a magnetic dead layer of ∼ 4 nm.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ch Domain walls and domain structure

Oscillatory exchange coupling in La0.67Sr0.33MnO3/SrTiO3 superlattices

S. J. Zhu, B. R. Zhao, B. Y. Zhu, B. Xu, L. X. Cao, and X. G. Qiu

Appl. Phys. Lett. 91, 012505 (2007); http://dx.doi.org/10.1063/1.2753707 (3 pages) | Cited 2 times

Online Publication Date: 3 July 2007

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The exchange bias effect has been observed in the superlattices consisting of ferromagnetic La0.67Sr0.33MnO3 and nonmagnetic insulating SrTiO3 layers. It is found that the exchange field shows an oscillatory decay with a period of ∼ 12 unit cells and approaches to a constant value of −100 Oe when the SrTiO3 thickness is increased. The tunneling current also displays a nonmonotonic decrease with the SrTiO3 thickness. These observations can be discussed on the basis of the interlayer exchange coupling between La0.67Sr0.33MnO3 layers via the spin-polarized electrons tunneling across the SrTiO3 spacers.
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75.30.Et Exchange and superexchange interactions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Gk Tunneling
72.25.Mk Spin transport through interfaces

ac susceptibility of a melt-textured YBa2Cu3Ox ring closed by a strong-coupling contact

D.-X. Chen, E. Pardo, and A. Sanchez

Appl. Phys. Lett. 91, 012506 (2007); http://dx.doi.org/10.1063/1.2753736 (3 pages) | Cited 4 times

Online Publication Date: 3 July 2007

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The complex ac susceptibility χ = χ′−jχ″ of a melt-textured YBa2Cu3Ox ring closed by a strong-coupling contact is measured after zero-field cooling to 77 K as a function of the ac field amplitude Hm and frequency f. The resulting χ(Hm,f) is similar to that derived from a power-law relation between the local current density and electric field but with maximum χ″(Hm) increasing steadily with increasing f, which is explained by the creep of Abrikosov-Josephson vortices along the contact driven by the London force of supercurrents and the Lorentz force of the induced normal currents.
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74.72.-h Cuprate superconductors
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

In situ scanning tunneling microscopy observations of polycrystalline MgO(001) tunneling barriers grown on amorphous CoFeB electrode

M. Mizuguchi, Y. Suzuki, T. Nagahama, and S. Yuasa

Appl. Phys. Lett. 91, 012507 (2007); http://dx.doi.org/10.1063/1.2754372 (3 pages) | Cited 4 times

Online Publication Date: 5 July 2007

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Topological surface analysis using in situ scanning tunneling microscopy was performed for highly oriented polycrystalline (textured) MgO(001) tunneling barrier layers grown on amorphous CoFeB electrode layers. The microscopy revealed a MgO surface structure in which nanosized grains were dispersed on clusters that originated from the CoFeB underlayer. In situ annealing reduced this surface roughness. Local tunneling spectroscopy measurements revealed the formation of a nearly perfect and uniform tunneling barrier in spite of grain boundaries in the textured MgO(001) layer, which is consistent with the fact that textured CoFeB/MgO/CoFeB and fully epitaxial MgO-based magnetic tunnel junctions exhibit comparable spin-dependent tunneling properties.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Bb Fe and its alloys
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Gh Other heat and thermomechanical treatments

Spin-polarized scanning tunneling microscopy in field emission mode

A. Kubetzka, M. Bode, and R. Wiesendanger

Appl. Phys. Lett. 91, 012508 (2007); http://dx.doi.org/10.1063/1.2753695 (3 pages) | Cited 7 times

Online Publication Date: 5 July 2007

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Image-potential states in front of the Fe(110) surface have been investigated by spin-polarized scanning tunneling spectroscopy. For the n = 1 state energetic splittings of up to 25 meV are observed in the spectroscopic data measured above oppositely magnetized surface areas. The technique offers the possibility to access the spin dependence of image-potential states on a local scale. These states can be used as a sensitive probe of surface magnetism, allowing high resolution magnetic imaging at tip-sample distances larger than in normal tunneling experiments, thereby reducing the probability of accidental tip-surface collisions.
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75.70.Rf Surface magnetism
75.50.Bb Fe and its alloys
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Effect of Pb on the low frequency Raman modes in Bi2−xPbxSr2CaCu2O8+δ and Bi2−xPbxSr2Ca2Cu3O10+δ superconductors

G. V. M. Williams

Appl. Phys. Lett. 91, 012509 (2007); http://dx.doi.org/10.1063/1.2753486 (3 pages)

Online Publication Date: 6 July 2007

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Low frequency Raman spectroscopy measurements have been made on Bi2−xPbxSr2CaCu2O8+δ and Bi2−xPbxSr2Ca2Cu3O10+δ high temperature superconductors. The frequency of the ∼ 118 cm−1 peak is found to correlate with the Pb content, and there is no correlation with the hole concentration in the CuO2 planes when it is varied by changing the oxygen content in the BiO layers. Thus, Raman measurements provide a means by which the Pb content can be estimated. When used in conjunction with measurements of the frequency of the O(2)SrA1g Raman mode, it is possible to also estimate the hole concentration in the CuO2 plane.
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74.25.Gz Optical properties
74.25.F- Transport properties
74.72.-h Cuprate superconductors

Giant magnetothermal conductivity in the Ni–Mn–In ferromagnetic shape memory alloys

B. Zhang, X. X. Zhang, S. Y. Yu, J. L. Chen, Z. X. Cao, and G. H. Wu

Appl. Phys. Lett. 91, 012510 (2007); http://dx.doi.org/10.1063/1.2753710 (3 pages) | Cited 32 times

Online Publication Date: 6 July 2007

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In this letter the authors present the observation of giant magnetothermal conductivity in NiMnIn single crystals. Upon cooling, a martensitic transformation is accompanied by a ferromagnetic metal→ferrimagnetic poor-metal transition. Most strikingly, this transition can be shifted to lower temperature and even totally suppressed by a magnetic field. The magnetic field-induced phase transition leads to a large magnetoresistance and a large magnetothermal conductivity up to 70% and 120%, respectively. The specific heat measurements indicate that the large magnetotransport properties are due to the increasing the density of free electrons, suggesting existence of superzone gap in the low-temperature, ferrimagnetic martensite.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
64.70.K- Solid-solid transitions
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
81.40.Rs Electrical and magnetic properties related to treatment conditions

Effect of substrate-induced strain on transport and magnetic properties of epitaxial La0.66Sr0.33MnO3 thin films

P. Dey, T. K. Nath, and A. Taraphder

Appl. Phys. Lett. 91, 012511 (2007); http://dx.doi.org/10.1063/1.2750399 (3 pages) | Cited 15 times

Online Publication Date: 6 July 2007

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Electrical transport and magnetic properties of epitaxial 500 Å La0.67Sr0.33MnO3 (LSMO) thin films, grown on different substrates having different lattice strains, are found to exhibit strong correlation with Jahn-Teller (JT) strain. The authors’ study reveals that a sufficiently large JT strain gives rise to distinct insulating state in LSMO films even below the respective para-ferromagnetic Curie temperature, which is a contradiction with the established phase diagram of Sr doped manganites. The authors have presented a microscopic model for the analysis of their data instead of the usual expansion around the undistorted state. The model incorporates two relevant eg orbitals and the effect of both JT and bulk strains on the transition temperature via double exchange.
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75.70.Ak Magnetic properties of monolayers and thin films
68.60.Bs Mechanical and acoustical properties
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.61.-r Electrical properties of specific thin films
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