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11 Jun 2012

Volume 100, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 241101 (2012); http://dx.doi.org/10.1063/1.4724309 (3 pages)

Miriam S. Vitiello, Leonardo Viti, Lorenzo Romeo, Daniele Ercolani, G. Scalari, J. Faist, F. Beltram, L. Sorba, and A. Tredicucci
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Size-dependent infrared properties of MgO nanoparticles with evidence of screening effect

Yann Chalopin, Hichem Dammak, Marc Hayoun, Mondher Besbes, and Jean-Jacques Greffet

Appl. Phys. Lett. 100, 241904 (2012); http://dx.doi.org/10.1063/1.4729384 (4 pages)

Online Publication Date: 14 June 2012

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We have investigated the infrared (IR) absorption properties of MgO nanoparticles (NPs) with the means of molecular dynamics simulations. Several size effects have been observed. We show in particular that the absorption of IR radiation does not occur predominantly through the polariton mode but preferentially through surface modes. This enhanced surface absorption is found to result from the absence of dielectric screening of the first atomic layer of the NPs. We demonstrate concomitantly that a macroscopic description of electrodynamics is inadequate to capture these unusual IR properties.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Long lifetime, high density single-crystal erbium compound nanowires as a high optical gain material

Leijun Yin, Hao Ning, Sunay Turkdogan, Zhicheng Liu, Patricia L. Nichols, and C. Z. Ning

Appl. Phys. Lett. 100, 241905 (2012); http://dx.doi.org/10.1063/1.4729412 (3 pages) | Cited 1 time

Online Publication Date: 14 June 2012

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Erbium-containing materials of long lifetime and high Er density are important for achieving strong luminescence and high optical gain in compact integrated photonics devices. We have systematically studied the lifetime and crystal quality as a function of growth conditions for an erbium compound that we recently reported, erbium chloride silicate (ECS). The lifetime for the best quality ECS nanowires can be as long as 540 μs, the longest for high-density Er-materials, representing a lifetime-density product as high as 8.7 × 1018 s cm−3. Such high density, long lifetime erbium materials can find many interesting applications such as compact lasers or amplifiers.
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81.16.-c Methods of micro- and nanofabrication and processing
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)
78.67.Uh Nanowires
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.55.Hx Other solid inorganic materials

Resolving the ultrafast dynamics of charge carriers in nanocomposites

J. Barreto, T. Roger, and A. Kaplan

Appl. Phys. Lett. 100, 241906 (2012); http://dx.doi.org/10.1063/1.4728120 (4 pages) | Cited 3 times

Online Publication Date: 14 June 2012

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Here, we describe an optical method to determine the dynamics of optically excited carriers in nanostructured composite samples. By combining pump-probe time-resolved reflectivity with scattering measurements, we extract the characteristic times for charge carrier evolution. We use the 3D Maxwell-Garnett formulae, modified to include the Drude optical response, to model the results. The method, applied to hydrogenated amorphous silicon containing crystalline silicon nanoparticles, showed that the recombination times in the nanocrystals and in the matrix were ∼4.9 ps and ∼22 ps, respectively. The charge transfer time between the crystals and the matrix was ∼4 ps.
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78.47.jg Time resolved reflection spectroscopy
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Jc Amorphous semiconductors; glasses
78.66.Jg Amorphous semiconductors; glasses

Coherently coupled ZnO and VO2 interface studied by photoluminescence and electrical transport across a phase transition

Amar Srivastava, T. S. Herng, Surajit Saha, Bao Nina, A. Annadi, N. Naomi, Z. Q. Liu, S. Dhar, Ariando, J. Ding, and T. Venkatesan

Appl. Phys. Lett. 100, 241907 (2012); http://dx.doi.org/10.1063/1.4729387 (4 pages)

Online Publication Date: 15 June 2012

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We have investigated the photoluminescence and electrical properties of a coherently coupled interface consisting of a ZnO layer grown on top of an oriented VO2 layer on sapphire across the phase transition of VO2. The band edge and defect luminescence of the ZnO overlayer exhibit hysteresis in opposite directions induced by the phase transition of VO2. Concomitantly the phase transition of VO2 was seen to induce defects in the ZnO layer. Such coherently coupled interfaces could be of use in characterizing the stability of a variety of interfaces in situ and also for novel device application.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
78.55.Hx Other solid inorganic materials
71.30.+h Metal-insulator transitions and other electronic transitions
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InGaN/GaN single-quantum-well microdisks

Yu-Chi Hsu (徐鈺淇), Ikai Lo (羅奕凱), Cheng-Hung Shih (施政宏), Wen-Yuan Pang (龐文淵), Chia-Hsuan Hu (胡嘉軒), Ying-Chieh Wang (王映傑), and Mitch M. C. Chou (周明奇)

Appl. Phys. Lett. 100, 242101 (2012); http://dx.doi.org/10.1063/1.4729007 (4 pages) | Cited 1 time

Online Publication Date: 11 June 2012

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We have grown InxGa1−xN/GaN quantum wells atop GaN microdisk with γ-LiAlO2 substrate by using plasma-assisted molecular beam epitaxy. The structural and optical properties of the samples were analyzed by transmission electron microscopy, x-ray diffraction, cathodoluminescence, and photoluminescence measurements. Based on the measured results, we obtained the indium concentration of the InxGa1−xN/GaN single quantum well to be x = 0.25 with a band-gap energy of 2.31 eV, which is consistent with the bowing effect of bulk InxGa1−xN: Eg(x) = [3.42 − x * 2.65 − x * (1 − x) * 2.4] eV.
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78.67.De Quantum wells
81.05.Ea III-V semiconductors
81.07.St Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.20.Nr Semiconductor compounds
78.55.Cr III-V semiconductors

Relationship between threading dislocation and leakage current in 4H-SiC diodes

Hirokazu Fujiwara, Hideki Naruoka, Masaki Konishi, Kimimori Hamada, Takashi Katsuno, Tsuyoshi Ishikawa, Yukihiko Watanabe, and Takeshi Endo

Appl. Phys. Lett. 100, 242102 (2012); http://dx.doi.org/10.1063/1.4718527 (4 pages) | Cited 3 times

Online Publication Date: 11 June 2012

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The impact of threading dislocation density on the leakage current of reverse current-voltage (I–V) characteristics in Schottky barrier diodes (SBDs), junction barrier Schottky diodes, and p-n junction diodes (PNDs) was investigated. The leakage current density and threading dislocation density have different positive correlations in each type of diode. Consequently, the correlation in SBDs is strong but weak in PNDs. Nano-scale inverted cone pits were observed at the Schottky junction interface, and it was found that leakage current increases in these diodes due to the concentration of electric fields at the peaks of the pits. The threading dislocations were found to be in the same location as the current leakage points in the SBDs but not in the PNDs.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices

Influence of linearly polarized radiation on magnetoresistance in irradiated two-dimensional electron systems

Jesús Iñarrea

Appl. Phys. Lett. 100, 242103 (2012); http://dx.doi.org/10.1063/1.4729299 (3 pages) | Cited 1 time

Online Publication Date: 11 June 2012

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We study the influence of the polarization angle of linear radiation on the radiation-induced magnetoresistance oscillations in two-dimensional electron systems and examine the polarization immunity on the temperature and quality of the sample. We have applied the radiation-driven electron orbits model obtaining that the magnetoresistance is affected by the orientation of the electric field of linearly polarized radiation when dealing with high quality samples and low temperatures. Yet, for lower quality samples and higher temperature, we recover polarization immunity in the radiation driven magnetoresistance oscillations. This could be of interest for future photoelectronics in high quality mesoscopic devices.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.63.-b Electronic transport in nanoscale materials and structures
78.20.Ls Magneto-optical effects

Photoexcited carrier dynamics in AlInN/GaN heterostructures

V. Liuolia, S. Marcinkevičius, D. Billingsley, M. Shatalov, J. Yang, R. Gaska, and M. S. Shur

Appl. Phys. Lett. 100, 242104 (2012); http://dx.doi.org/10.1063/1.4729033 (4 pages) | Cited 2 times

Online Publication Date: 12 June 2012

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Photoexcited carrier dynamics and localization potentials in Al0.86In0.14N/GaN heterostructures have been examined by time-resolved and scanning near-field photoluminescence (PL) spectroscopy. The large GaN and AlInN PL intensity difference, and the short AlInN PL decay and GaN PL rise times indicate efficient photoexcited hole transfer from AlInN to GaN via sub-band-gap states. These states are attributed to extended defects and In clusters. Near-field PL scans show that diameter of the localization sites and the distance between them are below 100 nm. Spatial variations of the GaN PL wavelength have been assigned to the electric field inhomogeneities at the heterostructure interface.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Cr III-V semiconductors
78.47.da Excited states
61.72.Nn Stacking faults and other planar or extended defects
71.20.Nr Semiconductor compounds
72.20.Fr Low-field transport and mobility; piezoresistance

Damping of optomechanical disks resonators vibrating in air

D. Parrain, C. Baker, T. Verdier, P. Senellart, A. Lemaitre, S. Ducci, G. Leo, and I. Favero

Appl. Phys. Lett. 100, 242105 (2012); http://dx.doi.org/10.1063/1.4729014 (4 pages)

Online Publication Date: 13 June 2012

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We report on miniature GaAs disk optomechanical resonators vibrating in air in the radiofrequency range. The flexural modes of the disks are studied by scanning electron microscopy and optical interferometry, and correctly modeled with the elasticity theory for annular plates. The mechanical damping is systematically measured, and confronted with original analytical models for air damping. Formulas are derived that correctly reproduce both the mechanical modes and the damping behavior, and can serve as design tools for optomechanical applications in fluidic environment.
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42.79.-e Optical elements, devices, and systems
46.40.Ff Resonance, damping, and dynamic stability
46.40.Jj Aeroelasticity and hydroelasticity
07.10.-h Mechanical instruments and equipment

Effect of the energy dependence of the carrier scattering time on the thermoelectric power factor of quantum wells and nanowires

Jane E. Cornett and Oded Rabin

Appl. Phys. Lett. 100, 242106 (2012); http://dx.doi.org/10.1063/1.4729381 (4 pages)

Online Publication Date: 13 June 2012

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The size-dependence of the thermoelectric power factor of thin-films and nanowires is theoretically investigated from the electric quantum limit (EQL) to the bulk-like regime. Different functional forms of the energy-dependent relaxation time τ(E) are incorporated in the model to account for carrier scattering mechanisms typical in semiconductor nanostructures. The calculations show that the steeper the increase in the relaxation time with carrier energy, the higher the power factor-to-average scattering time ratio, PF/〈τ〉, confirming the benefits of the preferential scattering of low-energy carriers to thermoelectric performance. However, outside the EQL, the power factor values are lower in the low-dimensional structures than in their three-dimensional counterparts. Thus, the power factor is more readily improved by modifications of the scattering rates than by quantization of the energy states.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.21.Hb Quantum wires

Intense monochromatic terahertz electromagnetic waves from coherent GaAs-like longitudinal optical phonons in (11n)-oriented GaAs/In0.1Al0.9As strained multiple quantum wells

Hideo Takeuchi, Souta Asai, Syuichi Tsuruta, and Masaaki Nakayama

Appl. Phys. Lett. 100, 242107 (2012); http://dx.doi.org/10.1063/1.4729125 (4 pages)

Online Publication Date: 15 June 2012

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We demonstrate that, in (11n)-oriented GaAs/In0.1Al0.9As strained multiple quantum wells, the terahertz electromagnetic wave from the coherent GaAs-like longitudinal optical (LO) phonon is enhanced by a piezoelectric field originating from a tensile strain in the GaAs layer. The presence of the tensile strain is confirmed using Raman scattering spectroscopy. The Fourier power spectrum of the terahertz waveform shows that the intensity of the terahertz band of the coherent GaAs-like LO phonon increases as the index n approaches 1. The amplitude of the GaAs-like LO phonon is proportional to the piezoelectric field in the strained GaAs layer.
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78.67.De Quantum wells
78.70.Gq Microwave and radio-frequency interactions
63.22.Np Layered systems
78.30.Fs III-V and II-VI semiconductors

Tunable device properties of free-standing inorganic/organic flexible hybrid structures obtained by exfoliation

Amitha Shetty and Karuna Kar Nanda

Appl. Phys. Lett. 100, 242108 (2012); http://dx.doi.org/10.1063/1.4729550 (5 pages) | Cited 1 time

Online Publication Date: 15 June 2012

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We report the fabrication of free-standing flexible inorganic/organic hybrid structures by exfoliating ZnO nanostructured films from the flat indium tin oxide (ITO)/silicon/sapphire substrates using poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). Strong interaction between ZnO and PEDOT:PSS and the thermomechanical response of PEDOT:PSS are the key issues for the exfoliation to prevail. The performance of the free-standing hybrid structures as rectifiers and photodetectors is better as compared to ITO supported hybrid structures. It is also shown that device properties of hybrid structures can be tuned by using different electrode materials.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
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Room temperature femtotesla radio-frequency atomic magnetometer

W. Chalupczak, R. M. Godun, S. Pustelny, and W. Gawlik

Appl. Phys. Lett. 100, 242401 (2012); http://dx.doi.org/10.1063/1.4729016 (4 pages)

Online Publication Date: 12 June 2012

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A radio-frequency tunable atomic magnetometer with a sensitivity of about 1 fT/Hz1/2 in a range of 10–500 kHz is demonstrated. The magnetometer is operated in the orientation configuration in which atoms are pumped to the stretched atomic state by a scheme based on indirect optical pumping using only one unmodulated, low-power laser. The magnetometer operates with cesium atoms, which have sufficient vapor pressure near room temperature to enable high magnetometric sensitivities. The technique enables a compact and robust module to be constructed that could become an in-the-field device.
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07.55.Ge Magnetometers for magnetic field measurements

Spin dynamics of magnetic nanostructures investigated by micromagnetic simulations

R. Rückriem, P. Krone, T. Schrefl, and M. Albrecht

Appl. Phys. Lett. 100, 242402 (2012); http://dx.doi.org/10.1063/1.4729054 (5 pages)

Online Publication Date: 12 June 2012

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Micromagnetic simulations were performed to investigate the spin dynamics of cylindrical magnetic nanostructures of various sizes down to 20 nm. The presented simulation technique provides information on the equilibrium states, magnetization precession, and spatial distributions of excited spin wave modes of individual nanostructures. Larger cylindrical nanostructures reveal a flower state magnetization configuration and show rather complex edge and center modes, which depend strongly on the saturation magnetization. This behavior allows controlling the precession frequencies, which is important in microwave-assisted three-dimensional magnetic recording, where layers of different resonance frequency need to be addressed and switched individually.
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75.75.Jn Dynamics of magnetic nanoparticles
75.78.Cd Micromagnetic simulations
75.30.Ds Spin waves
75.50.Tt Fine-particle systems; nanocrystalline materials

Large magnetic moment of gadolinium substituted topological insulator: Bi1.98Gd0.02Se3

Y. R. Song, Fang Yang, Meng-Yu Yao, Fengfeng Zhu, Lin Miao, Jin-Peng Xu, Mei-Xiao Wang, H. Li, X. Yao, Fuhao Ji, S. Qiao, Z. Sun, G. B. Zhang, B. Gao, Canhua Liu, et al.

Appl. Phys. Lett. 100, 242403 (2012); http://dx.doi.org/10.1063/1.4729056 (3 pages) | Cited 1 time

Online Publication Date: 12 June 2012

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The crystal structure, electronic, and magnetic properties of Gadolinium (Gd) substituted Bi2Se3—represented by Bi1.98Gd0.02Se3—were investigated systematically by scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and superconducting quantum interference device. Gd dopants with valence of 3+ were mainly found to substitute Bi atoms. Each Gd3+ ion has a magnetic moment as large as ∼6.9μB in the bulk paramagnetic state.
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75.30.Cr Saturation moments and magnetic susceptibilities
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.66.Fn Inorganic compounds
71.20.Ps Other inorganic compounds
75.20.Ck Nonmetals

Ferromagnetism of cobalt-doped anatase TiO2 studied by bulk- and surface-sensitive soft x-ray magnetic circular dichroism

V. R. Singh, K. Ishigami, V. K. Verma, G. Shibata, Y. Yamazaki, T. Kataoka, A. Fujimori, F.-H. Chang, D.-J. Huang, H.-J. Lin, C. T. Chen, Y. Yamada, T. Fukumura, and M. Kawasaki

Appl. Phys. Lett. 100, 242404 (2012); http://dx.doi.org/10.1063/1.4729123 (5 pages) | Cited 2 times

Online Publication Date: 12 June 2012

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We have studied magnetism in anatase Ti1−xCoxO2−δ (x = 0.05) thin films with various electron carrier densities, by soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L2,3 absorption edges. For electrically conducting samples, the magnetic moment estimated by XMCD was <0.3 μB/Co using the surface-sensitive total electron yield mode, while it was 0.3–2.4 μB/Co using the bulk-sensitive total fluorescence yield mode. The latter value is in the same range as the saturation magnetization 0.6–2.1 μB/Co deduced by SQUID measurement. The magnetization and the XMCD intensity increased with carrier density, consistent with the carrier-induced origin of the ferromagnetism.
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75.70.Ak Magnetic properties of monolayers and thin films
73.61.Le Other inorganic semiconductors
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic anisotropy engineering: Single-crystalline Fe films on ion eroded ripple surfaces

M. O. Liedke, M. Körner, K. Lenz, F. Grossmann, S. Facsko, and J. Fassbender

Appl. Phys. Lett. 100, 242405 (2012); http://dx.doi.org/10.1063/1.4729151 (4 pages)

Online Publication Date: 12 June 2012

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We present a method to preselect the direction of an induced in-plane uniaxial magnetic anisotropy (UMA) in thin single-crystalline Fe films on MgO(001). Ion beam irradiation is used to modulate the MgO(001) surface with periodic ripples on the nanoscale. The ripple direction determines the orientation of the UMA, whereas the intrinsic cubic anisotropy of the Fe film is not affected. Thus, it is possible to superimpose an in-plane UMA with a precision of a few degrees—a level of control not reported so far that can be relevant for example in spintronics.
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75.70.Ak Magnetic properties of monolayers and thin films
61.80.Jh Ion radiation effects
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys

Tunable misalignment of ferromagnetic and antiferromagnetic easy axes in exchange biased bilayers

R. L. Rodríguez-Suárez, L. H. Vilela-Leão, T. Bueno, J. B. S. Mendes, P. Landeros, S. M. Rezende, and A. Azevedo

Appl. Phys. Lett. 100, 242406 (2012); http://dx.doi.org/10.1063/1.4729040 (4 pages)

Online Publication Date: 13 June 2012

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In this paper we report experiments that show how to tune the unidirectional anisotropy field in exchange biased Ni81Fe19/Ir20Mn80 bilayers grown by sputtering. During growth the samples are held in an obliquely inclined stage, and simultaneously a static magnetic field is applied along an arbitrary direction in the film plane. While the direction of the ferromagnetic anisotropy field is given by the tilted columnar microstructures induced by the oblique sputtering, the direction of the unidirectional field can be tuned by the application of the in situ magnetic field. The magnetic properties were investigated using the ferromagnetic resonance technique.
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68.55.A- Nucleation and growth
73.40.Gk Tunneling
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
81.15.Cd Deposition by sputtering

On the Curie temperature dependency of the magnetocaloric effect

J. H. Belo, J. S. Amaral, A. M. Pereira, V. S. Amaral, and J. P. Araújo

Appl. Phys. Lett. 100, 242407 (2012); http://dx.doi.org/10.1063/1.4726110 (4 pages) | Cited 5 times

Online Publication Date: 13 June 2012

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We investigate the magnetocaloric effect dependency on the most important microscopic parameters of ferromagnetic materials, such as the Curie temperature (TC), the spin value (J), and the magnetic field change (ΔH). Second- and first-order phase transition systems are considered, using the Bean-Rodbell model [C. P. Bean and D. S. Rodbell, Phys. Rev. 126, 104 (1962)] of magnetovolume interactions on the Weiss mean-field model [P. Weiss, J. Phys. Theory Appl. 6, 661 (1907)]. The magnetocaloric effect simulations show a surprising TC−2/3 linear dependence of the maximum entropy change (ΔSmmax), which is observed for all simulated systems. An approximate state equation establishing the dependence of ΔSmmax on TC, ΔH, J, and the magnetic atoms density (N) is presented. The dependence of maximum magnetic entropy change on TC−2/3 is validated by a wide set of experimental results of second- and first-order phase transition materials that are promising for magnetic refrigeration applications at room temperature.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.80.+q Magnetomechanical effects, magnetostriction
65.40.gd Entropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Normal or inverse magnetocaloric effects at the transition between antiferromagnetism and ferromagnetism

Bing Li (李昺), Wen Liang (梁文), Weijun Ren (任卫军), Weijin Hu (胡卫进), Ji Li (李季), Changqing Jin (靳常青), and Zhidong Zhang (张志东)

Appl. Phys. Lett. 100, 242408 (2012); http://dx.doi.org/10.1063/1.4729122 (4 pages) | Cited 2 times

Online Publication Date: 13 June 2012

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The magnetocaloric effect (MCE) at the antiferromagnetic (AF) to ferromagnetic (F) phase transition in Mn1.05Ni0.85Ge and CrO1.86F0.14, and the MCE at the F-AF transition in Tb3Co have been investigated. Mn1.05Ni0.85Ge and CrO1.86F0.14 are found to exhibit the inverse MCE whereas the MCE of Tb3Co is normal. For these compounds, the dependence of the transition temperature on the applied magnetic field B has been studied. A thermodynamical analysis is presented of the sign of the magnetic-entropy change in these three compounds which are representatives of two different types of B-T diagrams. Other possible B-T diagrams are discussed and the analysis is extended to AF-F and F-AF phase transitions reported in literature.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Cc Other ferromagnetic metals and alloys
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
65.40.gd Entropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Domain wall configuration and magneto-transport properties in dual spin-valve with nanoconstriction

Byong Sun Chun, Han-Chun Wu, Su Jung Noh, In Chang Chu, Santiago Serrano-Guisan, Chanyong Hwang, Igor V. Shvets, Zhi-Min Liao, Mohamed Abid, and Young Keun Kim

Appl. Phys. Lett. 100, 242409 (2012); http://dx.doi.org/10.1063/1.4729126 (5 pages) | Cited 1 time

Online Publication Date: 13 June 2012

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We investigated the effect of external field on magneto-transport properties of synthetic antiferromagnet dual spin-valve with nanoconstriction with focus on domain wall (DW) configuration and magnetization reversal process. As magnetic field rotated from in-plane to out-of-plane along hard axis configuration, the magnetization reversal mode changed from a vortex to a transverse type, and a multistep switching process appeared due to the development of a transverse magnetization reversal mode with DW pushing towards the higher anisotropy region. The difference in the shape of nanoconstriction made an asymmetric energy barrier to the DW propagation which resulted in an asymmetry depinning field.
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75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms
61.46.-w Structure of nanoscale materials
75.50.Ee Antiferromagnetics
75.50.Kj Amorphous and quasicrystalline magnetic materials

Exchange bias effects in epitaxial Fe3O4/BiFeO3 heterostructures

T. L. Qu, Y. G. Zhao, P. Yu, H. C. Zhao, S. Zhang, and L. F. Yang

Appl. Phys. Lett. 100, 242410 (2012); http://dx.doi.org/10.1063/1.4729408 (4 pages) | Cited 5 times

Online Publication Date: 13 June 2012

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High quality Fe3O4 (5–20 nm)/BiFeO3 (BFO) heterostructures have been grown by pulsed laser deposition on (001) SrTiO3 (STO) substrates. Large exchange bias (EB) effects have been observed below 200 K in Fe3O4/BFO/STO structures compared with Fe3O4/STO structures. The exchange bias field decreases when increasing temperature or the thickness of Fe3O4 layer, and does not change after annealing in 0.1 T field from 700 K to room temperature across Neel temperature of BFO. A possible mechanism was proposed based on the interface spin coupling between Fe3O4 and BFO. Our work shed new light on the study of exchange bias effect in BFO system as well as the application for magnetoelectric devices.
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71.70.Gm Exchange interactions
75.30.Ds Spin waves
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.07.Bc Nanocrystalline materials
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition

Magnetization dynamics and reversal mechanism of Fe filled Ni80Fe20 antidot nanostructures

X. M. Liu, J. Ding, and A. O. Adeyeye

Appl. Phys. Lett. 100, 242411 (2012); http://dx.doi.org/10.1063/1.4729428 (5 pages)

Online Publication Date: 13 June 2012

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We investigate the magnetization dynamics and reversal mechanism of Fe filled Ni80Fe20 antidot nanostructures. The mutual magnetostatic coupling between the two ferromagnetic nanostructures leads to a significant modification to the magnetization reversal mechanism and ferromagnetic resonance mode profiles when compared with reference Fe dots and Ni80Fe20 antidot array. Our experimental results are in qualitative agreement with both the static and dynamic micromagnetic simulations.
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75.75.Jn Dynamics of magnetic nanoparticles
75.78.Cd Micromagnetic simulations
75.60.Jk Magnetization reversal mechanisms
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Ferromagnetic GeMn thin film prepared by ion implantation and ion beam induced epitaxial crystallization annealing

C. H. Chen, H. Niu, D. C. Yan, H. H. Hsieh, C. P. Lee, and C. C. Chi

Appl. Phys. Lett. 100, 242412 (2012); http://dx.doi.org/10.1063/1.4729752 (4 pages)

Online Publication Date: 15 June 2012

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Ferromagnetic GeMn was prepared by Mn implantation followed by ion beam-induced epitaxial crystallization annealing. The damage caused by Mn implantation was repaired by subsequent helium ion irradiation. Various structural analyses were performed and Mn ions were found to incorporate uniformly into the Ge lattice without the formation of any secondary phases. The remnant magnetic moment exhibited room temperature ferromagnetism. Anomalous Hall effect and field dependent magnetization were measured at the same time at room temperature indicating spin polarized free carrier transport. Additional measurement using x-ray magnetic circular dichroism also revealed that the carriers were spin-polarized.
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75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
68.55.ag Semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.-b Spin polarized transport
73.61.Cw Elemental semiconductors

Origin of magnetic anisotropy and spiral spin order in multiferroic BiFeO3

J. T. Zhang, X. M. Lu, J. Zhou, H. Sun, J. Su, C. C. Ju, F. Z. Huang, and J. S. Zhu

Appl. Phys. Lett. 100, 242413 (2012); http://dx.doi.org/10.1063/1.4729555 (4 pages) | Cited 1 time

Online Publication Date: 15 June 2012

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The first-principles calculations and thermodynamic modeling are combined to investigate the magnetic properties of BiFeO3. Our calculations indicate that the single-ion anisotropy and the anisotropic superexchange coupling contribute the same magnitude to the easy-magnetization-plane anisotropy. We show that the competition between the isotropic superexchange and the Dzyaloshinskii-Moriya interaction [I. Dzyaloshinsky, J. Phys. Chem. Solids 4, 241 (1958) and T. Moriya, Phys. Rev. 120, 91 (1960)] of the nearest-neighbor Fe spins provides the microscopic mechanism for the origin of the long period spiral spin order, and the induced spontaneous magnetization exhibits a sinusoidal arrangement under the spiral order.
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75.30.Gw Magnetic anisotropy
75.30.Ds Spin waves
75.78.-n Magnetization dynamics
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Et Exchange and superexchange interactions
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