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17 May 2010

Volume 96, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 96, 203102 (2010); http://dx.doi.org/10.1063/1.3429125 (3 pages)

Qimin Quan, Parag B. Deotare, and Marko Loncar
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Strongly suppressed 1/f noise and enhanced magnetoresistance in epitaxial Fe–V/MgO/Fe magnetic tunnel junctions

D. Herranz, F. Bonell, A. Gomez-Ibarlucea, S. Andrieu, F. Montaigne, R. Villar, C. Tiusan, and F. G. Aliev

Appl. Phys. Lett. 96, 202501 (2010); http://dx.doi.org/10.1063/1.3430064 (3 pages) | Cited 5 times

Online Publication Date: 17 May 2010

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Alloying Fe electrodes with V, through reduced FeV/MgO interface mismatch in epitaxial magnetic tunnel junctions with MgO barriers, notably suppresses both nonmagnetic (parallel) and magnetic (antiparallel) state 1/f noise and enhances tunneling magnetoresistance. A comparative study of the room temperature electron transport and low frequency noise in Fe1−xVx/MgO/Fe and Fe/MgO/Fe1−xVx magnetic tunnel junctions with 0 ≤ x ≤ 0.25 reveals that V doping of the bottom electrode for x<0.1 reduces in nearly two orders of magnitude the normalized nonmagnetic and magnetic 1/f noise. We attribute the enhanced TMR and suppressed 1/f noise to strongly reduced misfit and dislocation density.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport

Large exchange bias field in the Ni–Mn–Sn Heusler alloys with high content of Mn

H. C. Xuan, Q. Q. Cao, C. L. Zhang, S. C. Ma, S. Y. Chen, D. H. Wang, and Y. W. Du

Appl. Phys. Lett. 96, 202502 (2010); http://dx.doi.org/10.1063/1.3428782 (3 pages) | Cited 20 times

Online Publication Date: 17 May 2010

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The exchange bias properties have been investigated in bulk Mn50Ni40−xSn10+x (x = 0, 0.5, and 1) Heusler alloys with high content of Mn, in which the largest exchange bias field is up to 910 Oe for Mn50Ni40Sn10 alloy. In these alloys, the excess Mn atoms would occupy not only the Sn sites but also the Ni sites, and the moments of Mn on Sn or Ni sites are coupled antiferromagnetically to those on the regular Mn sites, respectively. The origin of this considerably large exchange bias field has been discussed.
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75.30.Et Exchange and superexchange interactions
71.70.Gm Exchange interactions
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
75.50.Ee Antiferromagnetics
75.30.Cr Saturation moments and magnetic susceptibilities

Positive surface and perpendicular magnetic anisotropy in natural nanomorphous Ni/NiO multilayers

P. Poulopoulos, V. Kapaklis, P. E. Jönsson, E. Th. Papaioannou, A. Delimitis, S. D. Pappas, D. Trachylis, and C. Politis

Appl. Phys. Lett. 96, 202503 (2010); http://dx.doi.org/10.1063/1.3428791 (3 pages) | Cited 2 times

Online Publication Date: 17 May 2010

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Ni/NiO multilayers with excellent sequencing are grown via radiofrequency magnetron sputtering with the use of one Ni target and natural oxidation. Ni layers consist of very small Ni nanocrystals interrupted by amorphous NiO layers. When Ni is deposited at 0.3 Pa Ar-pressure, the hard-magnetization axis is the film normal and saturation field decreases by decreasing Ni layer thickness. Considerable positive surface anisotropy is found, which is remarkable for Ni-based multilayers. If Ni is deposited at 3 Pa Ar-pressure, perpendicular magnetic anisotropy is observed at low temperatures even for 5.4 nm thick Ni layers. This anisotropy results in the formation of stripe magnetic domains.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure
75.78.Fg Dynamics of domain structures

C-axis critical current of a PrFeAsO0.7 single crystal

H. Kashiwaya, K. Shirai, T. Matsumoto, H. Shibata, H. Kambara, M. Ishikado, H. Eisaki, A. Iyo, S. Shamoto, I. Kurosawa, and S. Kashiwaya

Appl. Phys. Lett. 96, 202504 (2010); http://dx.doi.org/10.1063/1.3427464 (3 pages) | Cited 9 times

Online Publication Date: 18 May 2010

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The c-axis transport properties of a high-pressure synthesized PrFeAsO0.7 single crystal are studied using s-shaped junctions. Resistivity anisotropy of about 120 detected at 50 K shows the presence of strong anisotropy in the electronic states. The obtained critical current density for the c-axis of 2.9×105 A/cm2 is two orders of magnitude larger than that in Bi2Sr1.6La0.4CuO6+δ. The appearance of a hysteresis in the current-voltage curve below Tc is the manifestation of the intrinsic Josephson effect similar to that in cuprate superconductors. The suppression of the critical current-normal resistance (IcRn) product is explained by an inspecular transport in s±-wave pair potential.
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74.25.fc Electric and thermal conductivity
74.50.+r Tunneling phenomena; Josephson effects
74.25.Sv Critical currents
74.20.-z Theories and models of superconducting state

Potassium-doped BaFe2As2 superconducting thin films with a transition temperature of 40 K

Nam Hoon Lee, Soon-Gil Jung, Dong Ho Kim, and Won Nam Kang

Appl. Phys. Lett. 96, 202505 (2010); http://dx.doi.org/10.1063/1.3431583 (3 pages) | Cited 13 times

Online Publication Date: 18 May 2010

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We report the growth of potassium-doped BaFe2As2 thin films, where the major charge carriers are holes, on Al2O3 (0001) and LaAlO3 (001) substrates by using an ex situ pulsed laser deposition technique. The measured superconducting transition temperatures are 40 K and 39 K for the films grown on Al2O3 and LaAlO3, respectively, and diamagnetism indicates that the films have good bulk superconducting properties below 36 K and 30 K, respectively. The x-ray diffraction patterns for both films indicated a preferred c-axis orientation, regardless of the substrate structures of LaAlO3 and Al2O3. The upper critical field at zero temperature was estimated to be about 155 T.
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74.78.-w Superconducting films and low-dimensional structures
68.55.A- Nucleation and growth
74.62.-c Transition temperature variations, phase diagrams
81.15.Fg Pulsed laser ablation deposition
68.55.jm Texture

Reduced low frequency noise in electron beam evaporated MgO magnetic tunnel junctions

Z. Diao, J. F. Feng, H. Kurt, G. Feng, and J. M. D. Coey

Appl. Phys. Lett. 96, 202506 (2010); http://dx.doi.org/10.1063/1.3431620 (3 pages) | Cited 11 times

Online Publication Date: 18 May 2010

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We compare low frequency noise in magnetic tunnel junctions with MgO barriers prepared by electron-beam evaporation with those prepared by radiofrequency sputtering, both showing a high tunneling magnetoresistance. The normalized noise parameter in the parallel state of junctions with evaporated barriers is at least one order of magnitude lower than that in junctions with sputtered barriers, and exhibits a weaker bias dependence. The lowest normalized noise is in the 10−11 μm2 range. A lower density of oxygen vacancies acting as charge trap states in the evaporated MgO is responsible for the lower noise.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
61.72.jd Vacancies
72.20.My Galvanomagnetic and other magnetotransport effects

Enhanced microwave performance of cobalt nanoflakes with strong shape anisotropy

Fei Ma, Yong Qin, and Yun-Ze Li

Appl. Phys. Lett. 96, 202507 (2010); http://dx.doi.org/10.1063/1.3432441 (3 pages) | Cited 9 times

Online Publication Date: 19 May 2010

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Co nanoflakes are synthesized through a low temperature hydrothermal method. The single-phased hexagonal close-packed Co nanoflakes have a diameter of several micrometers and a thickness about 80 nm. Magnetic hysteresis loops are quite different along different directions deviating from the nanoflakes plane, which shows Co nanoflakes have strong magnetic anisotropy. Flakelike morphology influence the performance of complex permeability in gigahertz frequency. Natural resonance peak happens at 5.74 GHz with the contribution of shape anisotropy. Multiple resonance phenomenon appears due to the exchange resonance effect, which makes Co nanoflakes a broadband candidate for microwave absorbing material.
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75.75.-c Magnetic properties of nanostructures
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Control of orbital ordered state in strained Nd0.25Sr1.75MnO4 films

K. S. Takahashi, J. Fujioka, Y. Ida, M. Kawasaki, and Y. Tokura

Appl. Phys. Lett. 96, 202508 (2010); http://dx.doi.org/10.1063/1.3427428 (3 pages) | Cited 1 time

Online Publication Date: 19 May 2010

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Epitaxial strain effect has been studied for Nd0.25Sr1.75MnO4 thin films on (100) surfaces of two different isostructural (single-layered perovskite) substrates, LaSrAlO4 and LaSrGaO4. Due to the anisotropic strain in the MnO2 plane, the orientation-controlled films were stabilized with the structure consistent with that of C-type antiferromagnetic and d3x2−r2 ferro-orbital-ordered state. Measurements of highly anisotropic optical spectra show that the tensile strain in the MnO2 plane aligns ferroically the direction of d3x2−r2 orbitals parallel to the film plane, whereas compressive strain does those vertical to the film plane. These results indicate that the direction of the ferroic ordering of d3x2−r2 orbitals can be controlled by external uniaxial pressure, implying a potential for a switching device.
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68.55.-a Thin film structure and morphology
75.50.Ee Antiferromagnetics
77.80.-e Ferroelectricity and antiferroelectricity
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Shape-independent permeability model for uniaxially-anisotropic ferromagnetic thin films

Brice Jamieson, Terence O’Donnell, Santosh Kulkarni, and Saibal Roy

Appl. Phys. Lett. 96, 202509 (2010); http://dx.doi.org/10.1063/1.3430061 (3 pages) | Cited 1 time

Online Publication Date: 19 May 2010

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A permeability model based on the three-dimensional shape demagnetization effect is developed to estimate the permeability of any uniaxially-anisotropic ferromagnetic thin-film for integrated micromagnetic structures. The model is validated by comparison to measured ferromagnetic thin films (NiFe and CoPRe) with different anisotropies and saturation magnetizations. The dependence of permeability on film-thickness is modeled as a function of the demagnetization effect and verified against fabricated samples of varying thicknesses.
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75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Current-induced domain wall motion in Co/Pt nanowires: Separating spin torque and Oersted-field effects

J. Heinen, O. Boulle, K. Rousseau, G. Malinowski, M. Kläui, H. J. M. Swagten, B. Koopmans, C. Ulysse, and G. Faini

Appl. Phys. Lett. 96, 202510 (2010); http://dx.doi.org/10.1063/1.3405712 (3 pages) | Cited 13 times

Online Publication Date: 20 May 2010

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We report on low temperature current induced domain wall depinning experiments on (Co/Pt) multilayer nanowires with perpendicular magnetization. Using a special experimental scheme, we are able to extract the different contributions of the Oersted field and spin torque from the dependence of the depinning field on the injected current for selected magnetization configurations. The spin torque contribution is found to be dominant with a small contribution of the Oersted field leading to a nonadiabaticity factor β in line with previous measurements.
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75.60.Ch Domain walls and domain structure
81.07.Gf Nanowires
73.21.Ac Multilayers
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Effects of Mn concentration on the ac magnetically induced heating characteristics of superparamagnetic MnxZn1−xFe2O4 nanoparticles for hyperthermia

Minhong Jeun, Seung Je Moon, Hiroki Kobayashi, Hye Young Shin, Asahi Tomitaka, Yu Jeong Kim, Yasushi Takemura, Sun Ha Paek, Ki Ho Park, Kyung-Won Chung, and Seongtae Bae

Appl. Phys. Lett. 96, 202511 (2010); http://dx.doi.org/10.1063/1.3430043 (3 pages) | Cited 4 times

Online Publication Date: 21 May 2010

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The effects of Mn2+ cation concentration on the ac magnetically induced heating characteristics and the magnetic properties of superparamagnetic MnxZn1−xFe2O4 nanoparticles (SPNPs) were investigated to explore the biotechnical feasibility as a hyperthermia agent. Among the MnxZn1−xFe2O4 SPNPs, the Mn0.5Zn0.5Fe2O4 SPNP showed the highest ac magnetically induced heating temperature (ΔTac,mag), the highest specific absorption rate (SAR), and the highest biocompatibility. The higher out of phase susceptibility (χm″) value and the higher chemical stability systematically controlled by the replacement of Zn2+ cations by the Mn2+ cations on the A-site (tetrahedral site) are the primary physical reason for the promising biotechnical properties of Mn0.5Zn0.5Fe2O4 SPNP.
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87.85.Rs Nanotechnologies-applications
87.19.Pp Biothermics and thermal processes in biology

Atomically resolved scanning tunneling microscopy on perovskite manganite single crystals

Sahana Rößler, B. Padmanabhan, Suja Elizabeth, H. L. Bhat, F. Steglich, and S. Wirth

Appl. Phys. Lett. 96, 202512 (2010); http://dx.doi.org/10.1063/1.3432753 (3 pages) | Cited 1 time

Online Publication Date: 21 May 2010

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Atomically resolved scanning tunneling microscopy was conducted on cleaved single crystals of the cubic perovskite Pr0.68Pb0.32MnO3. Several different surface configurations could be resolved including a frequent square arrangement with atomic distances in excellent agreement to the bulk lattice constant of the cubic structure. We also observed stripe formation and a surface reconstruction. The latter is likely related to a polar rare earth-oxygen terminated surface.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.bt Other materials
61.66.Fn Inorganic compounds
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