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13 Sep 2010

Volume 97, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 113701 (2010); http://dx.doi.org/10.1063/1.3487998 (3 pages)

Sarah E. Baker, Michael D. Pocha, Allan S. P. Chang, Donald J. Sirbuly, Stefano Cabrini, Scott D. Dhuey, Tiziana C. Bond, and Sonia E. Létant
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Two-dimensional electron gas in Zn-polar ZnMgO/ZnO heterostructure grown by metal-organic vapor phase epitaxy

J. D. Ye, S. Pannirselvam, S. T. Lim, J. F. Bi, X. W. Sun, G. Q. Lo, and K. L. Teo

Appl. Phys. Lett. 97, 111908 (2010); http://dx.doi.org/10.1063/1.3489101 (3 pages) | Cited 7 times

Online Publication Date: 15 September 2010

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We report the formation of two-dimensional electron gas (2DEG) at the Zn1−xMgxO/ZnO interface grown by metal-organic vapor phase epitaxy on sapphire substrates. The existence of the 2DEG is confirmed by the observation of Shubnikov–de Haas oscillations and the integer quantum Hall effect. In particular, the Zn0.8Mg0.2O/ZnO heterostructure shows a high Hall mobility of 2138 cm2/V s with a carrier sheet density of 3.51×1012 cm−2 at 1.4 K. We attribute the origin of 2DEG to be the donor states on ZnMgO surface. The dependence of carrier sheet density of 2DEG on ZnMgO layer thickness and Mg composition (x) are also investigated.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
61.72.uj III-V and II-VI semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.A- Nucleation and growth
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.-i Conductivity phenomena in semiconductors and insulators
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Correlation of Mn charge state with the electrical resistivity of Mn doped indium tin oxide thin films

S. R. Sarath Kumar, Mohamed Nejib Hedhili, H. N. Alshareef, and S. Kasiviswanathan

Appl. Phys. Lett. 97, 111909 (2010); http://dx.doi.org/10.1063/1.3481800 (3 pages) | Cited 3 times

Online Publication Date: 15 September 2010

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Correlation of charge state of Mn with the increase in resistivity with Mn concentration is demonstrated in Mn-doped indium tin oxide films. Bonding analysis shows that Mn 2p3/2 core level can be deconvoluted into three components corresponding to Mn2+ and Mn4+ with binding energies 640.8 eV and 642.7 eV, respectively, and a Mn2+ satellite at ∼ 5.4 eV away from the Mn2+ peak. The presence of the satellite peak unambiguously proves that Mn exists in the +2 charge state. The ratio of concentration of Mn2+ to Mn4+ of ∼ 4:1 suggests that charge compensation occurs in the n-type films causing the resistivity increase.
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81.05.Hd Other semiconductors
73.61.Le Other inorganic semiconductors
71.15.Nc Total energy and cohesive energy calculations
61.50.Lt Crystal binding; cohesive energy

Energy band structure of the single crystalline MgO/n-Ge(001) heterojunction determined by x-ray photoelectron spectroscopy

Kun-Rok Jeon, Sang-Jun Lee, Chang-Yup Park, Hun-Sung Lee, and Sung-Chul Shin

Appl. Phys. Lett. 97, 111910 (2010); http://dx.doi.org/10.1063/1.3486116 (3 pages) | Cited 2 times

Online Publication Date: 16 September 2010

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We report the energy band structure of the single crystalline MgO/n-Ge(001) heterojunction characterized by x-ray photoelectron spectroscopy. The valence band offset of ΔEV = 3.64±0.07 eV with a 1.49±0.02 eV band bending was obtained. Given the experimental band gap of MgO (7.83 eV), a type-I band alignment with a conduction band offset of ΔEC = 3.52±0.07 eV is found. The band alignment of the MgO/n-Ge heterojunction including the large band bending was analyzed by a theoretical model taking into account the formation of the interface dipole.
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71.20.Nr Semiconductor compounds
79.60.Jv Interfaces; heterostructures; nanostructures
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Lattice site location of optical centers in GaN:Eu light emitting diode material grown by organometallic vapor phase epitaxy

K. Lorenz, E. Alves, I. S. Roqan, K. P. O’Donnell, A. Nishikawa, Y. Fujiwara, and M. Boćkowski

Appl. Phys. Lett. 97, 111911 (2010); http://dx.doi.org/10.1063/1.3489103 (3 pages) | Cited 6 times

Online Publication Date: 16 September 2010

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Eu-doped GaN was grown by organometallic vapor phase epitaxy at temperatures from 900 to 1100 °C. Eu incorporation is influenced by temperature with the highest concentration found for growth at 1000 °C. In all samples, Eu is incorporated entirely on substitutional Ga sites with a slight displacement which is highest ( ∼ 0.2 Å) in the sample grown at 900 °C and mainly directed along the c-axis. The major optical Eu3+ centers are identical for in situ doped and ion-implanted samples after high temperature and pressure annealing. The dominant Eu3+ luminescence lines are attributed to isolated, substitutional Eu.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.55.ag Semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Observation of electron confinement in InP/GaAs type-II ultrathin quantum wells

S. D. Singh, V. K. Dixit, S. Porwal, Ravi Kumar, A. K. Srivastava, Tapas Ganguli, T. K. Sharma, and S. M. Oak

Appl. Phys. Lett. 97, 111912 (2010); http://dx.doi.org/10.1063/1.3486470 (3 pages) | Cited 6 times

Online Publication Date: 17 September 2010

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The issue of type-II band alignment for InP/GaAs heterostructure is addressed by means of simple layer architecture of ultrathin quantum wells (QWs). From specific signatures of the radiative recombination in type-II QWs especially the cube root dependence of blueshift in the lowest excitonic transition energy on excitation power in photoluminescence measurements indicates that the observed luminescence is originating from spatially separated electrons and holes. Such a blueshift is seen to increase with the QW thickness again confirming a type-II band alignment. A direct evidence of electron confinement in the conduction band of InP is provided by the capacitance voltage measurements.
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68.65.Fg Quantum wells
81.07.St Quantum wells
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Cr III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.05.Ea III-V semiconductors
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Effects of the electroforming polarity on bipolar resistive switching characteristics of SrTiO3−δ films

X. B. Yan, Y. D. Xia, H. N. Xu, X. Gao, H. T. Li, R. Li, J. Yin, and Z. G. Liu

Appl. Phys. Lett. 97, 112101 (2010); http://dx.doi.org/10.1063/1.3488810 (3 pages) | Cited 15 times

Online Publication Date: 13 September 2010

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The effects of the electroforming polarity on the bipolar resistive switching characteristics in SrTiO3−δ thin films have been investigated. The conduction mechanisms of high resistance state and low resistance state are Poole–Frenkel emission and tunneling, respectively. The temperature dependences of the resistance at high and low resistance state are both semiconductorlike. The impact of the polarity of the electroforming voltage on the resistive switching mechanism and the distribution of defects was discussed. A simple model describing the combination of bulk and the interface effect was proposed to explain the resistive switching in this material.
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73.61.Ng Insulators
72.60.+g Mixed conductivity and conductivity transitions
73.50.Fq High-field and nonlinear effects
73.40.Gk Tunneling

Current-voltage characteristics of zinc-blende (cubic) Al0.3Ga0.7N/GaN double barrier resonant tunneling diodes

N. Zainal, S. V. Novikov, C. J. Mellor, C. T. Foxon, and A. J. Kent

Appl. Phys. Lett. 97, 112102 (2010); http://dx.doi.org/10.1063/1.3488819 (3 pages) | Cited 7 times

Online Publication Date: 13 September 2010

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Measurements of the current-voltage characteristics of zinc-blende (cubic) Al0.3Ga0.7N/GaN, double barrier resonant tunneling diodes are presented. Clear and reproducible negative differential resistance effects are observed, with room temperature peak-to-valley ratios up to 4 and peak currents up to about 1000 A cm−2.
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85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Surface, bulk, and interface electronic properties of nonpolar InN

W. M. Linhart, T. D. Veal, P. D. C. King, G. Koblmüller, C. S. Gallinat, J. S. Speck, and C. F. McConville

Appl. Phys. Lett. 97, 112103 (2010); http://dx.doi.org/10.1063/1.3488821 (3 pages) | Cited 7 times

Online Publication Date: 13 September 2010

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The electronic properties of a-plane and m-plane InN have been investigated by x-ray photoemission spectroscopy, infrared reflectivity, and surface space-charge calculations. Electron accumulation has been observed at the surface of nonpolar InN and the surface Fermi level has been found to be lower than previously observed on InN samples. A high electron density in the InN close to the interface with GaN was found in each nonpolar InN sample.
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73.20.At Surface states, band structure, electron density of states
71.20.Nr Semiconductor compounds
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Behaviors of InGaZnO thin film transistor under illuminated positive gate-bias stress

Te-Chih Chen, Ting-Chang Chang, Chih-Tsung Tsai, Tien-Yu Hsieh, Shih-Ching Chen, Chia-Sheng Lin, Ming-Chin Hung, Chun-Hao Tu, Jiun-Jye Chang, and Po-Lun Chen

Appl. Phys. Lett. 97, 112104 (2010); http://dx.doi.org/10.1063/1.3481676 (3 pages) | Cited 24 times

Online Publication Date: 14 September 2010

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In this letter, we investigate the impact of the light illumination on the stability of indium–gallium–zinc oxide thin film transistors under positive gate-bias stress. The noticeable decrease in threshold voltage (Vt) shift more than 5.5 V under illuminated positive gate-bias stress indicates a superior reliability in contrast with the dark stress. The accelerated Vt recovery characteristic compared with dark recovery demonstrates that the charge detrapping effect was enhanced under illumination. Furthermore, the average effective energy barrier of charge trapping and detrapping was derived to verify that illumination can excite the trapped charges and accelerate the charge detrapping process.
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85.30.Tv Field effect devices
81.05.Gc Amorphous semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Pz Photoconduction and photovoltaic effects

Thermoelectric properties of lattice-matched AlInN alloy grown by metal organic chemical vapor deposition

Hua Tong, Jing Zhang, Guangyu Liu, Juan A. Herbsommer, G. S. Huang, and Nelson Tansu

Appl. Phys. Lett. 97, 112105 (2010); http://dx.doi.org/10.1063/1.3489086 (3 pages) | Cited 23 times

Online Publication Date: 14 September 2010

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Thermoelectric properties of lattice-matched AlInN grown by metal organic chemical vapor deposition were measured and analyzed. The n-type Al0.83In0.17N alloy exhibited thermal conductivity of 4.87 W/(m K) measured by 3ω differential method. The Seebeck coefficient of n-Al0.83In0.17N was measured as −6.012×10−4 V/K by thermal gradient method. The sheet resistivity of n-Al0.83In0.17N was measured by using Van der Pauw method, and the electrical conductivity was measured as 2.38×104/(Ω m). The thermoelectric figure of merit (Z∗T) of n-type Al0.83In0.17N was measured as 0.532 at room temperature (T = 300 K). The finding indicates lattice-matched AlInN alloy on GaN as excellent material candidate for thermoelectric application.
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72.20.Pa Thermoelectric and thermomagnetic effects
66.70.Df Metals, alloys, and semiconductors
73.61.Ey III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Can silicon behave like graphene? A first-principles study

M. Houssa, G. Pourtois, V. V. Afanas’ev, and A. Stesmans

Appl. Phys. Lett. 97, 112106 (2010); http://dx.doi.org/10.1063/1.3489937 (3 pages) | Cited 25 times

Online Publication Date: 15 September 2010

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The electronic properties of two-dimensional hexagonal silicon (silicene) are investigated using first-principles simulations. Though silicene is predicted to be a gapless semiconductor, due to the sp2-hybridization of its atomic orbitals, the weak overlapping between 3pz orbitals of neighbor Si atoms leads to a very reactive surface, resulting in a more energetically stable semiconducting surface upon the adsorption of foreign chemical species. It is predicted that silicene inserted into a graphitelike lattice, like ultrathin AlN stacks, preserves its sp2-hydridization, and hence its graphenelike electronic properties.
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71.20.Mq Elemental semiconductors
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
68.43.Mn Adsorption kinetics

Multicarrier transport in epitaxial multilayer graphene

Yu-Ming Lin, Christos Dimitrakopoulos, Damon B. Farmer, Shu-Jen Han, Yanqing Wu, Wenjuan Zhu, D. Kurt Gaskill, Joseph L. Tedesco, Rachael L. Myers-Ward, Charles R. Eddy, Jr., Alfred Grill, and Phaedon Avouris

Appl. Phys. Lett. 97, 112107 (2010); http://dx.doi.org/10.1063/1.3485671 (3 pages) | Cited 11 times

Online Publication Date: 15 September 2010

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Variable-field Hall measurements were performed on epitaxial graphene grown on Si-face and C-face SiC. The carrier transport involves essentially a single-type of carrier in few-layer graphene, regardless of SiC face. However, in multilayer graphene (MLG) grown on C-face SiC, the Hall measurements indicated the existence of several groups of carriers with distinct mobilities. Electrical transport in MLG can be properly described by invoking three independent conduction channels in parallel. Two of these are n- and p-type, while the third involves nearly intrinsic graphene. The carriers in this lightly doped channel have significantly higher mobilities than the other two.
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72.80.Vp Electronic transport in graphene
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.up Other materials

Imaging of multinuclear spin system (I>1/2) in semiconductor microstructures using longitudinal-magnetization-detection nuclear magnetic resonance

Takashi Kawamura and Go Yusa

Appl. Phys. Lett. 97, 112108 (2010); http://dx.doi.org/10.1063/1.3490673 (3 pages)

Online Publication Date: 16 September 2010

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We propose a method for detecting the local nuclear spin in semiconductor microstructures using a nuclear magnetic resonance technique that detects the longitudinal magnetization (Mz) of nuclear spins. This technique involves manipulating the nuclear spin by applying a particular sequence of pulsed gradient and homogeneous magnetic fields. By calculating the time evolution of the density operators, we demonstrate that the local change in magnetization can be extracted from the change in the magnetization of the whole system. This technique is suitable for investigating microscopic semiconductor systems with a multinuclear spin of I>1/2.
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76.60.-k Nuclear magnetic resonance and relaxation
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Ds Spin waves

Charge transfer between epitaxial graphene and silicon carbide

Sergey Kopylov, Alexander Tzalenchuk, Sergey Kubatkin, and Vladimir I. Fal’ko

Appl. Phys. Lett. 97, 112109 (2010); http://dx.doi.org/10.1063/1.3487782 (3 pages) | Cited 14 times

Online Publication Date: 16 September 2010

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We analyze doping of graphene grown on SiC in two models which differ by the source of charge transferred to graphene, namely, from SiC surface and from bulk donors. For each of the two models, we find the maximum electron density induced in monolayer and bilayer graphene, which is determined by the difference between the work function for electrons in pristine graphene and donor states on/in SiC, and analyze the responsivity of graphene to the density variation by means of electrostatic gates.
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72.80.Vp Electronic transport in graphene
73.30.+y Surface double layers, Schottky barriers, and work functions
81.05.ue Graphene

Deep level transient spectroscopy in plasma-assisted molecular beam epitaxy grown Al0.2Ga0.8N/GaN interface and the rapid thermal annealing effect

Young S. Park, Minyoung Lee, Kiyoung Jeon, Im T. Yoon, Yoon Shon, Hyunsik Im, C. J. Park, Hoon Y. Cho, and Myung-Soo Han

Appl. Phys. Lett. 97, 112110 (2010); http://dx.doi.org/10.1063/1.3491798 (3 pages) | Cited 7 times

Online Publication Date: 17 September 2010

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We investigated deep-level traps formed in Al0.2Ga0.8N/GaN heterostructures grown using plasma-assisted molecular beam epitaxy and by performing deep level transient spectroscopy (DLTS). Two electron traps with activation energies of Ec−150 meV and Ec−250 meV were observed, and their capture cross-sections (σT) were estimated to be 2.0×10−18 cm2 and 1.1×10−17 cm2, respectively. Different behaviors in the dependence of DLTS on filling pulse length confirm that the traps originated from N vacancies and dislocations. The amplitude of the dislocation-induced DLTS signal was reduced significantly by high-temperature rapid thermal annealing under N2 ambient after hydrogen treatment due to the reduction in dislocation density.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
71.55.Eq III-V semiconductors
73.20.At Surface states, band structure, electron density of states
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Trapping-related recombination of charge carriers in silicon

N. P. Harder, R. Gogolin, and R. Brendel

Appl. Phys. Lett. 97, 112111 (2010); http://dx.doi.org/10.1063/1.3490240 (3 pages) | Cited 1 time

Online Publication Date: 17 September 2010

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We present experimental evidence and theoretical explanation for simultaneous occurrence of trapping related increased apparent carrier lifetime and decreased actual recombination lifetime in low injection. This correlation is not describable by the common Hornbeck and Haynes [Phys. Rev. 97, 311 (1955)] trapping model. McIntosh, Paudyal, and Macdonald [J. Appl. Phys. 104, 084503 (2008)] recently used Shockley–Read–Hall (SRH) recombination statistics [ Phys. Rev. 87, 835 (1952)] for describing the temperature dependence of trapping. Our study shows that these SRH statistics for traps also explain a causal connection between trapping-related increased apparent charge carrier lifetime and reduced actual lifetime in low injection.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors

Magnetoconcentration effect in intrinsic graphene ribbons

V. N. Sokolov, V. A. Kochelap, and K. W. Kim

Appl. Phys. Lett. 97, 112112 (2010); http://dx.doi.org/10.1063/1.3486124 (3 pages) | Cited 1 time

Online Publication Date: 17 September 2010

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We consider transverse redistributions of the electrons and holes in intrinsic graphene ribbons under the influence of crossed electric and magnetic fields, i.e., the magnetoconcentration effect. The electron and hole transport is described from the Boltzmann kinetic equation assuming the local quasiequilibrium distributions of the carriers over energy states. The effective control of the carriers is achieved from deep depletion to accumulation modes depending on the properties of the ribbon edges, provided electron-hole recombination/generation rates at the edges are different from those inside the ribbon. The current-voltage characteristics reflect the behavior of the carrier redistributions across the ribbon. The obtained results suggest that interesting effects such as the population inversion in certain ranges of energies and the induced transparency are possible, which make them attractive for various optoelectronics applications in the terahertz spectral range.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Ee Mobility edges; hopping transport
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Vp Electronic transport in graphene

Two-subband conduction in a gated high density InAlN/AlN/GaN heterostructure

H. Cheng, Ç. Kurdak, J. H. Leach, M. Wu, and H. Morkoç

Appl. Phys. Lett. 97, 112113 (2010); http://dx.doi.org/10.1063/1.3490248 (3 pages) | Cited 2 times

Online Publication Date: 17 September 2010

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Magnetotransport measurements on an In0.16Al0.84N/AlN/GaN gated Hall bar sample have been performed at 0.28 K. By the application of a gate voltage we were able to vary the total two-dimensional electron gas density from 1.83×1013 to 2.32×1013 cm−2. Two frequency Shubnikov–de Haas oscillations indicate occupation of two subbands by electrons. The density of electrons in the first and second sublevels are found to increase linearly with gate voltage with a slope of 2.01×1012 cm−2/V and 0.47×1012 cm−2/V, respectively. And the quantum lifetimes for the first and second subbands ranged from 0.55 to 0.95×10−13 s and from 1.2 to 2.1×10−13 s.
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81.05.Ea III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.20.At Surface states, band structure, electron density of states
72.20.My Galvanomagnetic and other magnetotransport effects
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Enhancement of magnetoresistance by hydrogen ion treatment for current-perpendicular-to-plane giant magnetoresistive films with a current-confined-path nano-oxide layer

H. Yuasa, M. Hara, S. Murakami, Y. Fuji, H. Fukuzawa, K. Zhang, M. Li, E. Schreck, P. Wang, and M. Chen

Appl. Phys. Lett. 97, 112501 (2010); http://dx.doi.org/10.1063/1.3486117 (3 pages) | Cited 3 times

Online Publication Date: 13 September 2010

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We have enhanced magnetoresistance (MR) for current-perpendicular-to-plane giant-magnetoresistive (CPP-GMR) films with a current-confined-path nano-oxide layer (CCP-NOL). In order to realize higher purity in Cu for CCPs, hydrogen ion treatment (HIT) was applied as the CuOx reduction process. By applying the HIT process, an MR ratio was increased to 27.4% even in the case of using conventional FeCo magnetic layer, from 13.0% for a reference without the HIT process. Atom probe tomography data confirmed oxygen reduction by the HIT process in the CCP-NOL. The relationship between oxygen counts and MR ratio indicates that further oxygen reduction would realize an MR ratio greater than 50%.
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75.50.Dd Nonmetallic ferromagnetic materials
81.65.-b Surface treatments
75.70.Ak Magnetic properties of monolayers and thin films
75.47.De Giant magnetoresistance

Enhanced spin signals due to native oxide formation in Ni80Fe20/Ag lateral spin valves

Goran Mihajlović, Daniel K. Schreiber, Yuzi Liu, John E. Pearson, Samuel D. Bader, Amanda K. Petford-Long, and Axel Hoffmann

Appl. Phys. Lett. 97, 112502 (2010); http://dx.doi.org/10.1063/1.3484141 (3 pages) | Cited 6 times

Online Publication Date: 13 September 2010

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Large nonlocal spin valve signals are reported in mesoscopic Ni80Fe20/Ag lateral spin valves upon exposing them to air. Magnetotransport measurements combined with transmission electron microscopy show that the formation of a native oxide layer at the Ni80Fe20/Ag interface is responsible for the large signals. The results indicate that lateral spin valves with superior performance to those based on high-resistance tunnel barriers can be achieved via controllable growth of native permalloy oxides.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.47.Np Metals and alloys

Size-dependent reversal of grains in perpendicular magnetic recording media measured by small-angle polarized neutron scattering

S. J. Lister, T. Thomson, J. Kohlbrecher, K. Takano, V. Venkataramana, S. J. Ray, M. P. Wismayer, M. A. de Vries, H. Do, Y. Ikeda, and S. L. Lee

Appl. Phys. Lett. 97, 112503 (2010); http://dx.doi.org/10.1063/1.3486680 (3 pages) | Cited 7 times

Online Publication Date: 13 September 2010

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Polarized small-angle neutron scattering has been used to measure the magnetic structure of a CoCrPt–SiOx thin-film data storage layer, contained within a writable perpendicular recording media, at granular (<10 nm) length scales. The magnetic contribution to the scattering is measured as the magnetization is reversed by an external field, providing unique spatial information on the switching process. A simple model of noninteracting nanomagnetic grains provides a good description of the data and an analysis of the grain-size dependent reversal provides strong evidence for an increase in magnetic anisotropy with grain diameter.
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75.50.Ss Magnetic recording materials
75.30.Gw Magnetic anisotropy
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.-d Domain effects, magnetization curves, and hysteresis
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Controllability of ferromagnetism in graphene

Tianxing Ma, Feiming Hu, Zhongbing Huang, and Hai-Qing Lin

Appl. Phys. Lett. 97, 112504 (2010); http://dx.doi.org/10.1063/1.3485059 (3 pages) | Cited 4 times

Online Publication Date: 13 September 2010

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We systematically study magnetic correlations in graphene within Hubbard model on a honeycomb lattice by using quantum Monte Carlo simulations. In the filling region below the Van Hove singularity, the system shows a short-range ferromagnetic correlation, which is slightly strengthened by the on-site Coulomb interaction and markedly by the next-nearest-neighbor hopping integral. The ferromagnetic properties depend on the electron filling strongly, which may be manipulated by the electric gate. Due to its resultant controllability of ferromagnetism, graphene-based samples may facilitate the development of many applications.
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75.75.-c Magnetic properties of nanostructures
75.10.Lp Band and itinerant models
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors

Enhanced magnetoresistance in lateral spin-valves

R. Adari, T. Patil, M. Murthy, R. Maheshwari, G. Vaidya, S. Ganguly, and D. Saha

Appl. Phys. Lett. 97, 112505 (2010); http://dx.doi.org/10.1063/1.3488818 (3 pages)

Online Publication Date: 14 September 2010

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The effect of feature sizes on the characteristics of lateral spintronic devices have been investigated experimentally and theoretically. It is demonstrated that confining spin-transport in the active region of a device enhances magnitude of the spin-dependent response substantially. Numerical simulation of spin-transport corroborates the experimental observations. Device characteristics are found to be a strong function of spin-polarizer and analyzer dimensions. The response is observed to attain a peak value for an optimum device feature size, and this is seen to be a function of temperature. Spin dependent effects become weaker for very small and very large devices.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.47.-m Magnetotransport phenomena; materials for magnetotransport
72.25.-b Spin polarized transport

Anisotropic magnetocaloric effect in all-ferromagnetic (La0.7Sr0.3MnO3/SrRuO3) superlattices

S. Thota, Q. Zhang, F. Guillou, U. Lüders, N. Barrier, W. Prellier, A. Wahl, and P. Padhan

Appl. Phys. Lett. 97, 112506 (2010); http://dx.doi.org/10.1063/1.3488828 (3 pages) | Cited 9 times

Online Publication Date: 14 September 2010

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We exploit the magnetic interlayer coupling in La0.7Sr0.3MnO3/SrRuO3 superlattices to realize a crossover between inverse and conventional magnetic entropy changes. Our data reveal a strong anisotropic nature of the magnetocaloric effect due to the magnetic anisotropy of the superlattice. Therefore, artificial superlattices built from ferromagnetic materials that can be used to alter the magnetic structure as well as the magnetic anisotropy, could also be utilized for tuning the magnetocaloric properties, which may open a constructive approach for magnetic refrigeration applications.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Gw Magnetic anisotropy
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Synthesis and magnetic properties of nanocrystals of cubic defect spinel MgMnO3

M. S. Seehra, V. Singh, S. Thota, B. Prasad, and J. Kumar

Appl. Phys. Lett. 97, 112507 (2010); http://dx.doi.org/10.1063/1.3489094 (3 pages) | Cited 4 times

Online Publication Date: 15 September 2010

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Synthesis and magnetic properties of nanocrystals (size ≃ 22 nm) of cubic spinel MgMnO3 with the defect structure [Mg2+][Mg1/32+Mn4/34+◻1/3]O4 are reported. Analysis of the magnetization M versus T (2–370 K) and M versus H (up to 65 kOe) data shows a blocking temperature TB ≃ 11 K and an estimated Néel temperature TN ∼ 150 K above which the Weiss temperature θ = −7 K and μ = 3.91 μB/Mn4+. For TB<T<TN, fit of the M versus H data to modified Langevin function yields 35 μB as magnetic moment/particle, resulting from the defect structure.
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75.75.Cd Fabrication of magnetic nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.-y Defects and impurities in crystals; microstructure
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.07.Bc Nanocrystalline materials
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