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4 Feb 2013

Volume 102, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 053102 (2013); http://dx.doi.org/10.1063/1.4789442 (5 pages)

P. H. Kim, C. Doolin, B. D. Hauer, A. J. R. MacDonald, M. R. Freeman, P. E. Barclay, and J. P. Davis
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Reconfigurable ground states in connected double-dot system

S. Jain, F. Y. Fradin, J. E. Pearson, V. Novosad, and S. D. Bader

Appl. Phys. Lett. 102, 052401 (2013); http://dx.doi.org/10.1063/1.4790144 (4 pages)

Online Publication Date: 4 February 2013

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Controlling the polarity of a vortex core in patterned magnetic arrays of double-dot systems was recently shown via a nonlinear spin dynamics manipulation procedure. In the present work, we utilize the microwave absorption amplitude to monitor this polarity switching transition as the excitation field is increased from the linear to nonlinear regime and back. A representative phase diagram is constructed for the two coupled-modes of the double dot system as a function of excitation frequency and amplitude.
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73.21.La Quantum dots
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.70.Gq Microwave and radio-frequency interactions
75.78.Jp Ultrafast magnetization dynamics and switching

Magnetic behavior of graphene sheets embedded carbon film originated from graphene nanocrystallite

Chao Wang and Dongfeng Diao

Appl. Phys. Lett. 102, 052402 (2013); http://dx.doi.org/10.1063/1.4790283 (4 pages) | Cited 1 time

Online Publication Date: 5 February 2013

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We found paramagnetic behavior at 300 K of graphene sheets embedded carbon (GSEC) film, which is deposited under low energy electron irradiation in electron cyclotron resonance plasma. The origin of the magnetic properties of GSEC film is ascribed to the formation of graphene nanocrystallite. With higher irradiation energy, the size of nanocrystallite barely changed, while the density in GSEC film became higher, leading to a dramatically increase of saturation magnetization and residual magnetism. This finding indicates that GSEC film with higher magnetization can be expected, which has the potential for magnetic and spintronics applications.
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75.70.Ak Magnetic properties of monolayers and thin films
76.40.+b Diamagnetic and cyclotron resonances
81.16.-c Methods of micro- and nanofabrication and processing
75.20.Ck Nonmetals
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Phase locking of vortex-based spin-torque nanocontact oscillators by antivortices

C. E. Zaspel

Appl. Phys. Lett. 102, 052403 (2013); http://dx.doi.org/10.1063/1.4790287 (4 pages)

Online Publication Date: 5 February 2013

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Magnetic vortices formed at a nanocontact undergo gyrotropic oscillations when driven by a spin-torque providing potential applications as microwave nano-oscillators; however, to increase the power output it is necessary to use an array of synchronized oscillators. Here a theory is developed for two nanocontact oscillators that are interacting through an intermediate antivortex. The confining potential for the two vortices formed at each nanocontact as well as the antivortex is the Oersted-Ampere field about each nanocontact. Solution of the Thiele equation for this system indicates that the nanocontact vortex oscillators will be phase locked over a wide range of nanocontact currents.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures

Correlation between write endurance and electrical low frequency noise in MgO based magnetic tunnel junctions

S. Amara-Dababi, H. Béa, R. C. Sousa, C. Baraduc, and B. Dieny

Appl. Phys. Lett. 102, 052404 (2013); http://dx.doi.org/10.1063/1.4788816 (4 pages)

Online Publication Date: 5 February 2013

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The write endurance and the 1/f noise of electrical origin were characterized in CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJ) for spin transfer torque or thermally assisted magnetic random access memories. A statistical study carried out on a set of 60 nominally identical patterned junctions of 200 nm diameter revealed a correlation trend between the electrical 1/f noise power in the unexercised MTJs and the number of write cycles that these MTJs can withstand before electrical breakdown. The junctions showing the largest 1/f noise power before the write endurance test (successive 30 ns pulses of 1.73 V) have the lowest endurance. In contrast, MTJs initially exhibiting lower 1/f noise tend to have a better electrical reliability, i.e., much longer write endurance. This correlation is explained by the presence of electron trapping sites in the MgO barrier and the role of electron trapping/detrapping phenomena in both MTJ reliability and its 1/f electrical noise power. These results suggest that 1/f noise could be used as a predictive characterization of the MTJ endurance.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
02.50.-r Probability theory, stochastic processes, and statistics
72.70.+m Noise processes and phenomena

Ultra-thin Co/Pd multilayers with enhanced high-temperature annealing stability

M. Gottwald, K. Lee, J. J. Kan, B. Ocker, J. Wrona, S. Tibus, J. Langer, S. H. Kang, and E. E. Fullerton

Appl. Phys. Lett. 102, 052405 (2013); http://dx.doi.org/10.1063/1.4791577 (4 pages)

Online Publication Date: 6 February 2013

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Understanding the thermal budget of perpendicular materials is crucial for the potential application perpendicular magnetic tunnel junctions. In this paper, we study the effects of high-temperature rapid thermal annealing on the structural and magnetic properties of ultra-thin Co/Pd multilayers deposited at room temperature. It is shown that perpendicular magnetic anisotropy of ultra-thin Co/Pd multilayers improves with increasing annealing temperature up to 425 °C. This property of ultra-thin Co/Pd multilayers provides increased thermal budgets for CMOS-integrated magnetic devices.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
81.40.Gh Other heat and thermomechanical treatments
68.65.Ac Multilayers
75.30.Gw Magnetic anisotropy

Embedded mask patterning: A nanopatterning process to fabricate FePt magnetic media

Hao Wang, Haibao Zhao, P. Quarterman, and Jian-Ping Wang

Appl. Phys. Lett. 102, 052406 (2013); http://dx.doi.org/10.1063/1.4791578 (4 pages)

Online Publication Date: 6 February 2013

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A nanopatterning process, named as the embedded mask patterning, was proposed and experimentally demonstrated based on the FePt recording media. A granular mask layer was deposited on top of a FePt continuous film. The granular pattern of the mask was then transferred down to FePt layer using reactive ion etching. Since controlling magnetic properties is separated from controlling granular nanostructure, FePt grains can be reduced by optimizing the mask layer and patterning process only. This process is also potentially compatible to any state-of-art vacuum process for other electronic devices wafers and heterostructured nanoparticles manufacturing.
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81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer
75.50.Ss Magnetic recording materials

Crystalline anisotropic magnetoresistance in quaternary ferromagnetic semiconductor (Ga,Mn)(As,Sb)

B. Howells, M. Wang, K. W. Edmonds, P. Wadley, R. P. Campion, A. W. Rushforth, C. T. Foxon, and B. L. Gallagher

Appl. Phys. Lett. 102, 052407 (2013); http://dx.doi.org/10.1063/1.4791580 (3 pages)

Online Publication Date: 6 February 2013

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We demonstrate a strong dependence of the anisotropic magnetoresistance (AMR) on the direction of current with respect to the crystalline axes in the quaternary diluted ferromagnetic semiconductor Ga0.94Mn0.06As0.9Sb0.1. Dominant cubic and uniaxial symmetries are observed for current along the [1math0] and [110] crystalline directions, respectively. In addition, an anomalous temperature dependence of the symmetry and magnitude of the AMR is observed. Phenomenological analysis reveals an important contribution of a crossed cubic crystalline/non-crystalline term, which is much larger than previously observed in (Ga,Mn)As films. Possible reasons for the enhancement of this term are discussed.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films

Space- and time-resolved Seebeck and Nernst voltages in laser-heated permalloy/gold microstructures

Arndt von Bieren, Florian Brandl, Dirk Grundler, and Jean-Philippe Ansermet

Appl. Phys. Lett. 102, 052408 (2013); http://dx.doi.org/10.1063/1.4789974 (4 pages)

Online Publication Date: 6 February 2013

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Thermoelectric effects in microstructured permalloy (Py)/Au wires are investigated using space- and time-resolved measurements based on scanning focused laser heating. Supported by numerical simulations of the temperature distribution, we identify two major contributions to the laser-induced signals: (i) the Seebeck effect due to thermocouples of Py/Au and (ii) the anomalous Nernst effect (ANE) in Py with a coefficient of NANE ≈ 1.6 μV/K. ANE-based magnetic imaging of magnetic domains and magnetization reversal is demonstrated with a lateral resolution on the μm scale.
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81.05.Bx Metals, semimetals, and alloys
81.40.Gh Other heat and thermomechanical treatments
72.15.Jf Thermoelectric and thermomagnetic effects
75.40.Mg Numerical simulation studies
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms
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