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6 Aug 2012

Volume 101, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 101, 062401 (2012); http://dx.doi.org/10.1063/1.4730997 (4 pages)

Mahdi Jamali, Kulothungasagaran Narayanapillai, Jae Hyun Kwon, and Hyunsoo Yang
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Detection of domain wall eigenfrequency in infinity-shaped magnetic nanostructures

Mahdi Jamali, Kulothungasagaran Narayanapillai, Jae Hyun Kwon, and Hyunsoo Yang

Appl. Phys. Lett. 101, 062401 (2012); http://dx.doi.org/10.1063/1.4730997 (4 pages)

Online Publication Date: 6 August 2012

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The dynamics of a magnetic infinity-shaped nanostructure has been experimentally studied by two different techniques such as the sinusoidal resonance excitation and the damped short pulse excitation to measure the eigenfrequency of domain walls. Direct observation of the magnetic domain wall nucleation has been measured in the frequency domain. Electrical measurements of the domain wall dynamics in the frequency domain reveal the existence of multi-eigenmodes for large excitation amplitudes. The time-resolved measurements show that the frequency of the damped gyration is similar to that of the frequency domain and indicate coexistence of spin wave excitations.
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75.60.Ch Domain walls and domain structure
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Ds Spin waves
02.10.Ud Linear algebra

Large half-metallic gap in ferromagnetic semi-Heusler alloys CoCrP and CoCrAs

Zhongyu Yao, Y. S. Zhang, and K. L. Yao

Appl. Phys. Lett. 101, 062402 (2012); http://dx.doi.org/10.1063/1.4742867 (4 pages)

Online Publication Date: 6 August 2012

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We investigate the electronic structure and magnetism of semi-Heusler alloys CoCrP and CoCrAs using the full-potential linearized augmented plane wave method. The calculations reveal that CoCrP and CoCrAs are half-metallic (HM) ferromagnets with the same magnetic moment of 2.00 μB per formula unit. Both alloys have large half-metallic gaps (up to 0.50 eV) and wide band gaps (above 1 eV). The half-metallicity of CoCrP and CoCrAs can be retained even when their lattice constants are changed by −4.8% to 6.6% and −7.7% to 4.5%, respectively. The two alloys show great promise in the applications of spin valve and magnetic tunnel junction.
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81.05.Bx Metals, semimetals, and alloys
61.66.Dk Alloys
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.20.Be Transition metals and alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Cc Other ferromagnetic metals and alloys

Interband dephasing and photon echo response in GaMnAs

M. Yildirim, S. March, R. Mathew, A. Gamouras, X. Liu, M. Dobrowolska, J. K. Furdyna, and K. C. Hall

Appl. Phys. Lett. 101, 062403 (2012); http://dx.doi.org/10.1063/1.4742916 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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Coherent carrier dynamics are studied in GaMnAs using time-integrated and time-resolved four-wave mixing techniques. Dephasing is observed to be dominated by spin-flip scattering between the optically injected holes and Mn ions, revealing the rapid time scale of this scattering process in the III-Mn-V diluted magnetic semiconductors. The optical response is shown to exhibit the characteristic signatures of a simple photon echo, despite the complexity of band tail contributions and strong exchange coupling in this system.
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78.47.jf Photon echoes
72.20.Fr Low-field transport and mobility; piezoresistance
75.50.Pp Magnetic semiconductors

Interlayer magnetostatic coupling and linear magnetoresistance in [Pd/Co]/MgO/Co junction sensor

C. Song, Y. Y. Wang, X. J. Li, G. Y. Wang, and F. Pan

Appl. Phys. Lett. 101, 062404 (2012); http://dx.doi.org/10.1063/1.4742999 (4 pages)

Online Publication Date: 6 August 2012

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We investigate interlayer magnetostatic coupling and linear magnetoresistance in [Pd/Co]/MgO/Co and [Pd/Co]/MgO/Co/MgO/[Co/Pd] tunnel junctions, where Co/Pd and Co ferromagnetic layers exhibit out-of-plane and in-plane magnetic anisotropy, respectively. Because of the magnetostatic interaction between Co moments and the stray field from Co/Pd stripe domains, the Co layer shows a significant enhancement of coercivity and exchange bias. Linear magnetoresistance is observed in both junctions in the field up to 15 kOe with the current perpendicular to the film plane, due to coherent rotation of the ferromagnets, making junctions with MgO barrier and orthogonal magnetization configuration a promising high magnetic field sensor.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.30.Gw Magnetic anisotropy
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
07.55.-w Magnetic instruments and components

Magnetic properties of phthalocyanine-based organometallic nanowire

Yandong Ma, Ying Dai, Zhenkui Zhang, Lin Yu, and Baibiao Huang

Appl. Phys. Lett. 101, 062405 (2012); http://dx.doi.org/10.1063/1.4744437 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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Using first principles calculations, we investigate the electronic and magnetic properties of transition metal phthalocyanine (M-Pc, M = Cr, Mn, Co, Ni, Cu, and Zn) nanowire (M-PcNW). Our calculations show that Ni-PcNW and Zn-PcNW are nonmagnetic, while Cr-PcNW and Cu-PcNW are antiferromagnetic with small energy difference and Co-PcNW show paramagnetic due to their long spin coherence length. Most importantly, we predicate that Mn-PcNW frameworks display long-ranged ferromagnetic spin ordering, offering strong spin polarization around Fermi level. Moreover, Mn-PcNW frameworks are half-metals, which make Mn-PcNW frameworks ideal candidates for spintronic devices. These results may shed light on further experimental studies on molecular spintronics.
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61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.22.-f Electronic structure of nanoscale materials and related systems

Magnetoelectric effects at microwave frequencies on Z-type hexaferrite

Khabat Ebnabbasi, Marjan Mohebbi, and Carmine Vittoria

Appl. Phys. Lett. 101, 062406 (2012); http://dx.doi.org/10.1063/1.4744591 (3 pages) | Cited 3 times

Online Publication Date: 6 August 2012

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Converse microwave measurements have been performed to measure magnetoelectric effects at room temperature on Sr3Co2Fe24O41 hexaferrite slabs. The measured properties include the magnetic permeability and strain as a function of the electric field E. In this paper, the microwave permeability changes are due to the application of a DC voltage affecting the static magnetization rather than shifts in ferromagnetic resonance. We conclude that when an electric field is turned on the ferrite exhibits broken symmetries for time reversal and parity.
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75.85.+t Magnetoelectric effects, multiferroics
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Influence of thermal fluctuations on the emission linewidth in MgO-based spin transfer oscillators

J. F. Sierra, M. Quinsat, F. Garcia-Sanchez, U. Ebels, I. Joumard, A. S. Jenkins, B. Dieny, M.-C. Cyrille, A. Zeltser, and J. A. Katine

Appl. Phys. Lett. 101, 062407 (2012); http://dx.doi.org/10.1063/1.4744924 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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The temperature dependence of the microwave emission linewidth Δf, the amplitude-phase coupling parameter ν, and the amplitude relaxation rate Γp were investigated experimentally for tunnel junction spin-transfer-oscillators. A linear increase of Δf and unexpectedly of Γp with temperature is observed, giving a ratio 2πΔf/Γp close to one. Analytical evaluation of the phase variance confirms that for this ratio the temperature dependence of Δf is linear and that in this temperature range Δf is enhanced by the amplitude-phase coupling. This is not changed when taking the temperature dependence of Γp into account, the origin of which remains to be elucidated.
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84.30.Ng Oscillators, pulse generators, and function generators
84.40.-x Radiowave and microwave (including millimeter wave) technology

Current-induced synchronized switching of magnetization

Soo-Man Seo and Kyung-Jin Lee

Appl. Phys. Lett. 101, 062408 (2012); http://dx.doi.org/10.1063/1.4742917 (5 pages) | Cited 2 times

Online Publication Date: 7 August 2012

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We investigate current-induced magnetization switching for a multilayer structure that allows a reduced switching current while maintaining high thermal stability of the magnetization. The structure consists of a perpendicular polarizer, a perpendicular free-layer, and an additional free-layer having in-plane magnetization. When the current runs perpendicular to the structure, the in-plane free-layer undergoes a precession and supplies an internal rf field to the perpendicular free-layer, resulting in a reduced switching current for one current polarity. For the other polarity, the in-plane free-layer almost saturates perpendicular to the plane and acts as another perpendicular polarizer, which also reduces the switching current.
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75.60.-d Domain effects, magnetization curves, and hysteresis
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
75.30.Gw Magnetic anisotropy
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.40.Mg Numerical simulation studies

Electrical determination of relative chirality direction in a Co/Cu/Co ferromagnetic ring

A. S. Demiray, M. Kohda, T. Miyawaki, Y. Watanabe, K. Saito, S. Mitani, K. Takanashi, and J. Nitta

Appl. Phys. Lett. 101, 062409 (2012); http://dx.doi.org/10.1063/1.4743004 (5 pages)

Online Publication Date: 7 August 2012

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We have studied a Co/Cu/Co trilayer circular ring by using a current-in-plane giant magnetoresistance (GMR) method. When the applied field angle is shifted from the current probes, four distinctive magnetization reversal patterns are obtained depending on the vortex chirality configurations in the top and bottom rings. During the repeated GMR measurements, two GMR patterns are preferentially appeared and it turns out that the same chirality is favorable between the top and the bottom rings. Micromagnetic simulation reproduces the experimental data by taking into account the domain wall shift at the onion states.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms

Carrier-dopant exchange interactions in Mn-doped PbS colloidal quantum dots

Gen Long, Biplob Barman, Savas Delikanli, Yu Tsung Tsai, Peihong Zhang, Athos Petrou, and Hao Zeng

Appl. Phys. Lett. 101, 062410 (2012); http://dx.doi.org/10.1063/1.4743010 (4 pages)

Online Publication Date: 7 August 2012

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Carrier-dopant exchange interactions in Mn-doped PbS colloidal quantum dots were studied by circularly polarized magneto-photoluminescence. Mn substitutional doping leads to paramagnetic behavior down to 5 K. While undoped quantum dots show negative circular polarization, Mn doping changes its sign to positive. A circular polarization value of 40% was achieved at T = 7 K and B = 7 tesla. The results are interpreted in terms of Zeeman splitting of the band edge states in the presence of carrier-dopant exchange interactions that are qualitatively different from the s,p-d exchange interactions in II-VI systems.
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78.20.Ls Magneto-optical effects
78.55.Hx Other solid inorganic materials
61.72.up Other materials
75.20.Ck Nonmetals
75.30.Et Exchange and superexchange interactions
75.50.Pp Magnetic semiconductors

Mechanism of the giant irreversible positive magnetic entropy change in a Tb-based bulk metallic glass

Qiang Luo, Björn Schwarz, Norbert Mattern, Jun Shen, and Jürgen Eckert

Appl. Phys. Lett. 101, 062411 (2012); http://dx.doi.org/10.1063/1.4743014 (5 pages)

Online Publication Date: 7 August 2012

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A suitable coherent description of the reversible and irreversible magnetic entropy changes in a Tb-based metallic glass with strong random magnetic anisotropy (RMA) is presented. A giant irreversible positive magnetic entropy change is observed from magnetic measurements at low temperatures, which is found to arise from the entropy production, while a small negative one is obtained from heat capacity measurements. The temperature dependences of the irreversible positive magnetic entropy change under a field change of 5 T and the internal entropy production in the initial magnetization process can be described by an exponential law, which is determined by RMA.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.43.Fs Glasses
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
72.15.Jf Thermoelectric and thermomagnetic effects
75.30.Gw Magnetic anisotropy
75.50.Kj Amorphous and quasicrystalline magnetic materials

Nanoscale magnetic tunnel junction sensors with perpendicular anisotropy sensing layer

Z. M. Zeng, P. Khalili Amiri, J. A. Katine, J. Langer, K. L. Wang, and H. W. Jiang

Appl. Phys. Lett. 101, 062412 (2012); http://dx.doi.org/10.1063/1.4744914 (4 pages)

Online Publication Date: 7 August 2012

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A nano-scale linear magnetoresistance sensor is demonstrated using magnetic tunnel junctions with an in-plane magnetized reference layer and a sensing layer with interfacial perpendicular anisotropy. We show that the sensor response depends critically on the thickness of the sensing layer since its perpendicular anisotropy is significantly associated with thickness. The optimized sensors exhibit a large field sensitivity of up to 0.02% MR/Oe and a high linear field range of up to 600 Oe. These findings imply that this sensing scheme is a promising method for developing nano-scale magnetic sensors with simple design, high sensitivity, and low power consumption.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems
07.55.-w Magnetic instruments and components
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Accurate determination of the specific absorption rate in superparamagnetic nanoparticles under non-adiabatic conditions

F. J. Teran, C. Casado, N. Mikuszeit, G. Salas, A. Bollero, M. P. Morales, J. Camarero, and R. Miranda

Appl. Phys. Lett. 101, 062413 (2012); http://dx.doi.org/10.1063/1.4742918 (4 pages) | Cited 2 times

Online Publication Date: 8 August 2012

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We report on a general description of non-adiabatic calorimetry measurements for improving the accuracy on the determination of the specific absorption rate of superparamagnetic nanoparticles subjected to alternating magnetic fields. We perform experiments on reduced volumes of iron oxide nanoparticles dispersed in aqueous media under different thermal equilibrium conditions. We introduce a simple model, which considers linear thermal losses to precisely reproduce the complete time evolution of temperature. The control and the quantification of heat losses lead to higher accuracy for determining the specific absorption rate in superparamagnetic nanoparticles.
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75.75.Jn Dynamics of magnetic nanoparticles
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
75.50.Tt Fine-particle systems; nanocrystalline materials
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Generating electron cyclotron resonance plasma using distributed scheme

C. C. Huang, T. H. Chang, N. C. Chen, H. W. Chao, C. C. Chen, and S. F. Chou

Appl. Phys. Lett. 101, 062414 (2012); http://dx.doi.org/10.1063/1.4745189 (3 pages)

Online Publication Date: 8 August 2012

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This study employs a distributed microwave input system and permanent magnets to generate large-area electron cyclotron resonance (ECR) plasma. ECR plasmas were generated with nitrogen gas, and the plasma density was measured by Langmuir probe. A uniform ECR plasma with the electron density fluctuation of ±9.8% over 500 mm × 500 mm was reported. The proposed idea of generating uniform ECR plasma can be scaled to a much larger area by using n × n microwave input array system together with well-designed permanent magnets.
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52.50.Dg Plasma sources
52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena

Magnetic domain wall induced, localized nanowire reversal

L. O’Brien, A. Beguivin, A. Fernandez-Pacheco, D. Petit, D. E. Read, and R. P. Cowburn

Appl. Phys. Lett. 101, 062415 (2012); http://dx.doi.org/10.1063/1.4742746 (5 pages) | Cited 1 time

Online Publication Date: 9 August 2012

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Considerable difficulties exist in generating appreciable magnetic fields, localized on nanometer length scales for future experiments and technologies. Here we experimentally demonstrate selective reversal of a ferromagnetic nanowire by the stray field from a domain wall. The use of a domain wall as a persistent, mobile source of magnetic field is an alternative to localized Oersted fields and current induced switching, with possible use in future domain wall based data storage schemes and magnetic random access memory applications.
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75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms

Origin of ferromagnetism enhancement in bi-layer chromium-doped indium zinc oxides

C. Y. Hsu

Appl. Phys. Lett. 101, 062416 (2012); http://dx.doi.org/10.1063/1.4745845 (5 pages)

Online Publication Date: 9 August 2012

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This work demonstrates that by controlling the rapid thermal annealing temperature, amorphous chromium-doped indium zinc oxide films develop an amorphous-crystalline bi-layer structure and show magnetization up to ∼30 emu/cm3. The crystalline layer arises from significant out-diffusion of Zn from surfaces, leading to a large difference in the Zn:In ratio in amorphous and crystalline layers. Doped Cr ions in amorphous and crystalline layers form different valence configurations, creating a charge reservoir which transfers electrons through amorphous-crystalline interfaces and in turn enhances ferromagnetism.
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75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
73.21.Ac Multilayers
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