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25 Jun 2012

Volume 100, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 261104 (2012); http://dx.doi.org/10.1063/1.4711253 (4 pages)

Marcelo Davanço, Jun Rong Ong, Andrea Bahgat Shehata, Alberto Tosi, Imad Agha, Solomon Assefa, Fengnian Xia, William M. J. Green, Shayan Mookherjea, and Kartik Srinivasan
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Direct evidence for stress-induced (001) anisotropy of rapid-annealed FePt thin films

S. N. Hsiao, S. H. Liu, S. K. Chen, T. S. Chin, and H. Y. Lee

Appl. Phys. Lett. 100, 261909 (2012); http://dx.doi.org/10.1063/1.4730963 (4 pages) | Cited 4 times

Online Publication Date: 28 June 2012

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Roles of rapid thermal annealing (RTA) on the evolution of crystallographic anisotropy of single-layered FePt films have been characterized. We observed a huge biaxial tensile stress of 2.18 GPa induced with increasing heating rate from 0.5 to 40 K/s. The result is a transition of orientation from (111) to perfect (001) texture. The later then degrades at heating rates ≥80 K/s due to morphological variation. The advantages of RTA are to induce tensile stress by densification reaction within a very short time and to simultaneously impede thickness-dependent dynamic stress relaxation.
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75.70.Ak Magnetic properties of monolayers and thin films
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.55.jm Texture
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Bs Mechanical and acoustical properties
75.30.Gw Magnetic anisotropy

Resonant cavity modes in gallium oxide microwires

Iñaki López, Emilio Nogales, Bianchi Méndez, and Javier Piqueras

Appl. Phys. Lett. 100, 261910 (2012); http://dx.doi.org/10.1063/1.4732153 (3 pages) | Cited 3 times

Online Publication Date: 28 June 2012

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Fabry Perot resonant modes in the optical range 660–770 nm have been detected from single and coupled Cr doped gallium oxide microwires at room temperature. The luminescence is due to chromium ions and dominated by the broad band involving the 4T2–4A2 transition, strongly coupled to phonons, which could be of interest in tunable lasers. The confinement of the emitted photons leads to resonant modes detected at both ends of the wires. The separation wavelength between maxima follows the Fabry-Perot dependence on the wire length and the group refractive index for the Ga2O3 microwires.
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81.05.Hd Other semiconductors
78.67.Uh Nanowires
81.07.Gf Nanowires
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.55.Hx Other solid inorganic materials

Coherent phonon dynamics at the martensitic phase transition of Ni2MnGa

S. O. Mariager, A. Caviezel, P. Beaud, C. Quitmann, and G. Ingold

Appl. Phys. Lett. 100, 261911 (2012); http://dx.doi.org/10.1063/1.4730946 (4 pages)

Online Publication Date: 29 June 2012

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We use time-resolved optical reflectivity to study the laser stimulated dynamics in the magnetic shape memory alloy Ni2MnGa. We observe two coherent optical phonons, at 1.2 THz in the martensite phase and at 0.7 THz in the pre-martensite phase, which we interpret as a zone-folded acoustic phonon and a heavily damped amplitudon, respectively. In the martensite phase the martensitic phase transition can be induced by a fs laser pulse on a timescale of a few ps.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
64.70.kd Metals and alloys
78.47.jg Time resolved reflection spectroscopy
81.30.Kf Martensitic transformations
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity

Orientation-dependent hardness and strain rate sensitivity in nanotwin copper

J. C. Ye, Y. M. Wang, T. W. Barbee, Jr., and A. V. Hamza

Appl. Phys. Lett. 100, 261912 (2012); http://dx.doi.org/10.1063/1.4731242 (5 pages) | Cited 4 times

Online Publication Date: 29 June 2012

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We observe a strong twin-orientation dependent hardness and strain rate sensitivity (m) in nanotwin copper. A highest m value of 0.059 ± 0.004 and an activation volume (V) of ∼10b3 are measured when deformation is predominately vertical to twin boundaries (TBs), whereas a much smaller m and larger V are observed for the direction parallel to TBs. Dislocation density is found to have a stronger impact on m and V in nanotwin materials, compared to that in coarse-grained materials.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Mm Grain and twin boundaries
62.20.Qp Friction, tribology, and hardness
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

A “universal” criterion for metallic glass formation

Li-Min Wang, Yongjun Tian, Riping Liu, and Weihua Wang

Appl. Phys. Lett. 100, 261913 (2012); http://dx.doi.org/10.1063/1.4731881 (4 pages) | Cited 1 time

Online Publication Date: 29 June 2012

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We have established a generally applicable criterion for the critical cooling rates Rc needed for the formation of metallic glasses, based on thermodynamic and kinetic properties of ten categories of metal-based alloys ranging from binary to multicomponent systems. Rc is found to depend on several fundamental properties of materials including the glass transition temperature (normalized with respect to the liquidus temperature), entropy of fusion, and kinetic fragility. Such a relation reproduces the experimental Rc values of 43 metallic glasses remarkably well with a R2 value of 0.94. The explanation of Rc provides guidance in search of metallic glasses.
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64.70.qd Thermodynamics and statistical mechanics
61.43.Fs Glasses
82.60.Fa Heat capacities and heats of phase transitions
82.60.Lf Thermodynamics of solutions
64.70.dj Melting of specific substances
64.70.pe Metallic glasses
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Influence of Coulomb interaction on the electrical transport properties of ultrathin Al:ZnO films

Yang Yang, Yu-Jie Zhang, Xin-Dian Liu, and Zhi-Qing Li

Appl. Phys. Lett. 100, 262101 (2012); http://dx.doi.org/10.1063/1.4730947 (4 pages) | Cited 1 time

Online Publication Date: 25 June 2012

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We have measured the Hall coefficient RH and the electrical conductivity σ of a series of ultrathin (∼55 nm) Al:ZnO films. These films reveal mesoscopic characteristics in electrical transport properties, i.e., both RH and σ obey lnT law in a wide temperature range (from liquid-helium temperatures to ∼100 K for RH and from liquid-helium temperatures up to several tens K for σ). These observations not only disclose the fundamental physical properties of the ultrathin Al:ZnO films but also provide strong evidences for the validity of the current theories concerning the electron-electron interaction in granular metals.
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73.61.Ga II-VI semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects

Correlation between threading dislocation density and sheet resistance of AlGaN/AlN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy

Stephen W. Kaun, Man Hoi Wong, Umesh K. Mishra, and James S. Speck

Appl. Phys. Lett. 100, 262102 (2012); http://dx.doi.org/10.1063/1.4730951 (4 pages) | Cited 3 times

Online Publication Date: 25 June 2012

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AlGaN/AlN/GaN heterostructures were grown on 6H-SiC, GaN-on-sapphire, and free-standing GaN, resulting in heterostructures with threading dislocation densities of ∼2 × 1010, ∼5 × 108, and ∼5 × 107 cm−2, respectively. Growths were carried out under Ga-rich conditions by plasma-assisted molecular beam epitaxy to determine the influence of threading dislocation density on the sheet resistance of AlGaN/AlN/GaN heterostructures. High threading dislocation density was observed to significantly degrade Hall mobility. An AlGaN/AlN/GaN heterostructure with a ∼2 nm AlN interlayer and a threading dislocation density of ∼5 × 107 cm−2 achieved the very low room temperature sheet resistance of 175 Ω/□.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

AlSb nucleation induced anisotropic electron mobility in AlSb/InAs heterostructures on GaAs

L. Desplanque, S. El Kazzi, J.-L. Codron, Y. Wang, P. Ruterana, G. Moschetti, J. Grahn, and X. Wallart

Appl. Phys. Lett. 100, 262103 (2012); http://dx.doi.org/10.1063/1.4730958 (4 pages) | Cited 1 time

Online Publication Date: 25 June 2012

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The influence of the growth conditions at the AlSb/GaAs interface on the electron mobility in AlSb/InAs heterostructures is investigated. We show that an excessive antimony flux during the initial stage of the AlSb buffer growth leads to a strong anisotropy of electron mobility in InAs between [110] and [1-10] crystallographic orientations. This anisotropy is attributed to the formation of trenches oriented along the [1-10] direction in the InAs channel. Transmission electron microscopy reveals that these trenches are directly related to twinning defects originating from the AlSb/GaAs interface.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.Mm Grain and twin boundaries
72.20.Fr Low-field transport and mobility; piezoresistance

Effects of doping on the lattice parameter of SrTiO3

Anderson Janotti, Bharat Jalan, Susanne Stemmer, and Chris G. Van de Walle

Appl. Phys. Lett. 100, 262104 (2012); http://dx.doi.org/10.1063/1.4730998 (3 pages) | Cited 1 time

Online Publication Date: 27 June 2012

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The effects on the lattice parameter due to incorporation of high concentrations of donor impurities in SrTiO3 are examined both experimentally and theoretically. Experimental lattice parameters were obtained from x-ray diffraction on La-doped films grown on bulk SrTiO3 substrates with carrier concentrations up to 2 × 1021 cm−3. The observed increase in lattice parameter is attributed to two causes: impurity-size and electronic effects. The latter can be attributed in part to the energy gain by lowering the conduction band upon volume expansion. These contributions are evaluated explicitly using hybrid functional calculations, with a net result in very good agreement with experiment.
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68.55.-a Thin film structure and morphology
61.72.sd Impurity concentration
71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.61.Ng Insulators

Direct measurement of surface states density and energy distribution in individual InAs nanowires

E. Halpern, G. Elias, A. V. Kretinin, H. Shtrikman, and Y. Rosenwaks

Appl. Phys. Lett. 100, 262105 (2012); http://dx.doi.org/10.1063/1.4731211 (4 pages)

Online Publication Date: 27 June 2012

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InAs nanowires are candidates for future high-speed electronic and optoelectronic applications due to their high electron mobility and large coherence length. However, InAs surfaces are known to possess a high concentration of donor-type surface states, which results in an electron accumulation layer and, consequently, Fermi level pinning. Since the surface to volume ratio in nanowires is very large, the effect of surface states is greatly enhanced. We present a method for directly determining the density and energy distribution of single nanowire surface states using Kelvin probe force microscopy measured on a nanowire field-effect transistor and interpreted by electrostatic modeling. Here, the method is applied to individual InAs nanowires, which similarly to bulk InAs exhibit a prominent accumulation layer consisting of a large concentration of donor-type surface states. Nevertheless, due to the small diameter of the nanowires, the electron accumulation and Fermi level pinning take place within the entire nanowire.
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73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.22.Dj Single particle states
71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds

Switching-time analysis of binary-oxide memristors via a nonlinear model

Nabeem Hashem and Shamik Das

Appl. Phys. Lett. 100, 262106 (2012); http://dx.doi.org/10.1063/1.4726421 (3 pages)

Online Publication Date: 27 June 2012

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A simulation-based analysis is conducted of the ionic switching times for nanometer-scale binary-oxide “memristor” devices. This analysis is based upon a device model that incorporates nonlinear field-driven ionic transport within the bulk of the memristor. In contrast, prior models of charge transport in such devices have relied upon linear simplifications, or else they have included nonlinear effects only at the electrode interfaces. As shown here via simulation, the nonlinear model provides much closer quantitative agreement with experimentally observed device switching times. Also, this model predicts a distinct asymmetry between the “set” and “reset” switching behaviors of memristors that is not present in linear models. Thus, the model and the quantitative results derived using it suggest an experimental route by which the underlying device physics might be elucidated further.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)

Improvement of oxygen vacancy migration through Nb doping on Ba0.7Sr0.3TiO3 thin films for resistance switching random access memory application

Chang Hwa Jung, Moon Kyu Park, and Seong Ihl Woo

Appl. Phys. Lett. 100, 262107 (2012); http://dx.doi.org/10.1063/1.4730400 (5 pages)

Online Publication Date: 27 June 2012

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Undoped and Nb-doped Ba0.7Sr0.3TiO3 (BST) thin films were fabricated by RF magnetron sputtering. The bipolar resistance switching behaviors of both thin films were observed with the stable endurance by DC voltage sweep. Nb doping in BST influenced the defect distribution and improved the uniformity of resistance switching random access memory (ReRAM) properties. The defect distribution was strongly related to the resistance switching properties and the decrease in the grain size caused by Nb doping made the oxygen migration more efficient. The oxygen migration in BST was assisted by Nb dopants which increased the concentration of the non-lattice oxygen in BST layer during ReRAM operation.
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84.30.Sk Pulse and digital circuits
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.15.Cd Deposition by sputtering
68.55.at Other materials

Enhanced electrical and noise properties of nanocomposite vanadium oxide thin films by reactive pulsed-dc magnetron sputtering

H. A. Basantani, S. Kozlowski, Myung-Yoon Lee, J. Li, E. C. Dickey, T. N. Jackson, S. S. N. Bharadwaja, and M. Horn

Appl. Phys. Lett. 100, 262108 (2012); http://dx.doi.org/10.1063/1.4731240 (4 pages) | Cited 1 time

Online Publication Date: 28 June 2012

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Thin films of VOx (1.3 ≤ x ≤ 2) were deposited by reactive pulsed-dc magnetron sputtering of a vanadium metal target while RF-biasing the substrate. Rutherford back scattering, glancing angle x-ray, and cross-sectional transmission electron microscopy measurements revealed the formation of nanocolumns with nanotwins within VOx samples. The resistivity of nanotwinned VOx films ranged from 4 mΩ·cm to 0.6 Ω·cm and corresponding temperature coefficient of resistance between −0.1% and −2.6% per K, respectively. The 1/f electrical noise was analyzed in these VOx samples using the Hooge-Vandamme relation. These VOx films are comparable or surpass commercial VOx films deposited by ion beam sputtering.
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73.61.Ng Insulators
61.72.Mm Grain and twin boundaries
81.15.Cd Deposition by sputtering
68.55.aj Insulators
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing

Selection rule of preferred doping site for n-type oxides

Chong Li, Jingbo Li, Shu-Shen Li, Jian-Bai Xia, and Su-Huai Wei

Appl. Phys. Lett. 100, 262109 (2012); http://dx.doi.org/10.1063/1.4731766 (4 pages)

Online Publication Date: 28 June 2012

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Using first-principles calculations and analysis, we show that to create shallow n-type dopants in oxides, anion site doping is preferred for more covalent oxides such as SnO2 and cation site doping is preferred for more ionic oxides such as ZnO. This is because for more ionic oxides, the conduction band minimum (CBM) state actually contains a considerable amount of O 3s orbitals, thus anion site doping can cause large perturbation on the CBM and consequently produces deeper donor levels. We also show that whether it is cation site doping or anion site doping, the oxygen-poor condition should always be used.
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61.72.uj III-V and II-VI semiconductors
61.72.up Other materials
71.20.Nr Semiconductor compounds
71.55.Gs II-VI semiconductors

Mechanism of formation of the misfit dislocations at the cubic materials interfaces

Yi Wang, P. Ruterana, S. Kret, J. Chen, S. El Kazzi, L. Desplanque, and X. Wallart

Appl. Phys. Lett. 100, 262110 (2012); http://dx.doi.org/10.1063/1.4731787 (5 pages) | Cited 2 times

Online Publication Date: 29 June 2012

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High-angle annular dark-field scanning transmission electron microscopy and molecular dynamic simulation are applied to study the misfit dislocations at the GaSb/GaAs interface. In the investigated samples, three types of misfit dislocations have been observed: shuffle and glide set Lomer dislocations and 60° dislocation pairs. The dislocation density tensor analysis is next used to quantify the Burgers vector of misfit dislocations and investigate the misfit dislocation formation mechanism. This work demonstrates that, in these hetero-structures, the dominant mechanism underlying the formation of misfit dislocations is the glide and reaction of 60° dislocations. It is shown that the final structure of each misfit dislocation depends on the Burgers vectors of the initial 60° dislocations. Finally, this analysis points out an approach to determine the local rotation at interface due to mixed type dislocations.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Large-size porous ZnO flakes with superior gas-sensing performance

Wei Wen, Jin-Ming Wu, and Yu-De Wang

Appl. Phys. Lett. 100, 262111 (2012); http://dx.doi.org/10.1063/1.4731876 (4 pages) | Cited 4 times

Online Publication Date: 29 June 2012

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A simple top-down route is developed to fabricate large size porous ZnO flakes via solution combustion synthesis followed by a subsequent calcination in air, which is template-free and can be easily enlarged to an industrial scale. The achieved porous ZnO flakes, which are tens to hundreds of micrometers in flat and tens of nanometers in thickness, exhibit high response for detecting acetone and ethanol, because the unique two-dimensional architecture shortens effectively the gas diffusion distance and provides highly accessible open channels and active surfaces for the target gas.
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81.05.Rm Porous materials; granular materials
81.16.-c Methods of micro- and nanofabrication and processing
81.05.Cy Elemental semiconductors
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
61.43.Gt Powders, porous materials
81.05.Dz II-VI semiconductors
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Temperature-driven nucleation of ferromagnetic domains in FeRh thin films

C. Baldasseroni, C. Bordel, A. X. Gray, A. M. Kaiser, F. Kronast, J. Herrero-Albillos, C. M. Schneider, C. S. Fadley, and F. Hellman

Appl. Phys. Lett. 100, 262401 (2012); http://dx.doi.org/10.1063/1.4730957 (5 pages) | Cited 1 time

Online Publication Date: 25 June 2012

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The evolution of ferromagnetic (FM) domains across the temperature-driven antiferromagnetic (AF) to FM phase transition in uncapped and capped epitaxial FeRh thin films was studied by x-ray magnetic circular dichroism and photoemission electron microscopy. The coexistence of the AF and FM phases was evidenced across the broad transition and the different stages of nucleation, growth, and coalescence were directly imaged. The FM phase nucleates into single domain islands and the width of the transition of an individual nucleus is sharper than that of the transition in a macroscopic average.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
78.20.Ls Magneto-optical effects
78.66.Bz Metals and metallic alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films

Magnetic Schottky diode exploiting spin polarized transport in Co/p-Si heterostructure

A. Sarkar, R. Adhikari, and A. K. Das

Appl. Phys. Lett. 100, 262402 (2012); http://dx.doi.org/10.1063/1.4730960 (4 pages) | Cited 1 time

Online Publication Date: 25 June 2012

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Magnetic Schottky heterojunction fabricated from Co/p-Si is investigated. The diode showed proper rectifying property at all temperatures and evolution of a giant positive junction magnetoresistance is observed at temperatures below 50 K. Based on a simplified band structure, the spin polarization of the device is determined to be ∼31% at 10 K. A phenomenological model is proposed to explain the observed spintronic behavior of the device.
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85.30.Kk Junction diodes
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Field orientation dependent decorrelation of magnetization reversal in uniaxial Co-films

J. A. Arregi, O. Idigoras, P. Vavassori, and A. Berger

Appl. Phys. Lett. 100, 262403 (2012); http://dx.doi.org/10.1063/1.4730956 (4 pages) | Cited 1 time

Online Publication Date: 26 June 2012

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Magnetization reversal correlation is studied as a function of the applied field angle for thin Co-films showing in-plane uniaxial magnetocrystalline anisotropy. We find that the field orientation angle has a profound effect onto the magnetization reversal process leading to a suppression of long-range correlation at sufficiently large field angles in the presence of grain alignment disorder. Correspondingly, this behavior allows for a tuning and the local confinement of magnetization reversal even in strongly exchange-coupled films and therefore presents a most desirable scenario for ultrahigh density magnetic recording.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.50.Ss Magnetic recording materials
75.60.Jk Magnetization reversal mechanisms

Diffusive model of current-in-plane-tunneling in double magnetic tunnel junctions

P.-Y. Clement, C. Ducruet, C. Baraduc, M. Chshiev, and B. Diény

Appl. Phys. Lett. 100, 262404 (2012); http://dx.doi.org/10.1063/1.4730961 (4 pages)

Online Publication Date: 26 June 2012

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We propose a model that describes current-in-plane tunneling transport in double barrier magnetic tunnel junctions in diffusive regime. Our study shows that specific features appear in double junctions that are described by introducing two typical length scales. The model may be used to measure the magnetoresistance and the resistance area product of both barriers in unpatterned stacks of double barrier magnetic tunnel junctions.
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75.47.Pq Other materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
66.30.-h Diffusion in solids

Thickness dependent magnetic properties of (Ga,Mn)As ultrathin films

O. Proselkov, D. Sztenkiel, W. Stefanowicz, M. Aleszkiewicz, J. Sadowski, T. Dietl, and M. Sawicki

Appl. Phys. Lett. 100, 262405 (2012); http://dx.doi.org/10.1063/1.4731202 (4 pages) | Cited 4 times

Online Publication Date: 26 June 2012

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We report on a monotonic reduction of Curie temperature in dilute ferromagnetic semiconductor (Ga,Mn)As upon a well controlled chemical-etching/oxidizing thinning from 15 nm down to complete removal of the ferromagnetic response. The effect already starts at the very beginning of the thinning process and is accompanied by the spin reorientation transition of the in-plane uniaxial anisotropy. We postulate that a negative gradient along the growth direction of self-compensating defects (Mn interstitial) and the presence of surface donor traps gives quantitative account on these effects within the p–d mean field Zener model with adequate modifications to take a nonuniform distribution of holes and Mn cations into account.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.jd Thickness
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Pp Magnetic semiconductors
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
73.50.Fq High-field and nonlinear effects

Broadband probing magnetization dynamics of the coupled vortex state permalloy layers in nanopillars

A. A. Awad, A. Lara, V. Metlushko, K. Y. Guslienko, and F. G. Aliev

Appl. Phys. Lett. 100, 262406 (2012); http://dx.doi.org/10.1063/1.4729825 (4 pages) | Cited 2 times

Online Publication Date: 26 June 2012

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Broadband magnetization response of coupled vortex state magnetic dots in layered nanopillars was explored as a function of in-plane magnetic field and interlayer separation. For dipolarly coupled circular Py(25 nm)/Cu(20 nm)/Py(25 nm) nanopillars of 600 nm diameter, a small in-plane field splits the eigenfrequencies of azimuthal spin wave modes inducing an abrupt transition between in-phase and out-of-phase kinds of the low-lying coupled spin wave modes. The critical field for this splitting is determined by antiparallel chiralities of the vortices in the layers. Qualitatively similar (although more gradual) changes occur also in the exchange coupled Py(25 nm)/Cu(1 nm)/Py(25 nm) tri-layer nanopillars. These findings are in qualitative agreement with micromagnetic dynamic simulations.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.75.-c Magnetic properties of nanostructures
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Effect of “dipolar-biasing” on the tunability of tunneling magnetoresistance in transition metal oxide systems

P. Anil Kumar and D. D. Sarma

Appl. Phys. Lett. 100, 262407 (2012); http://dx.doi.org/10.1063/1.4731206 (4 pages)

Online Publication Date: 27 June 2012

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We observe an unusual tunneling magnetoresistance (TMR) phenomenon in a composite of La2/3Sr1/3MnO3 with CoFe2O4 where the TMR versus applied magnetic field loop suggests a “negative coercive field.” Tracing its origin back to a “dipolar-biasing” of La2/3Sr1/3MnO3 by CoFe2O4, we show that the TMR of even a single composite can be tuned continuously so that the resistance peak or the highest sensitivity of the TMR can be positioned anywhere on the magnetic field axis with a suitable magnetic history of the sample. This phenomenon of an unprecedented tunability of the TMR should be present in general in all such composites.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.-m Magnetotransport phenomena; materials for magnetotransport

Asymmetric Pt/Co/Pt-stack induced sign-control of current-induced magnetic domain-wall creep

R. Lavrijsen, P. P. J. Haazen, E. Murè, J. H. Franken, J. T. Kohlhepp, H. J. M. Swagten, and B. Koopmans

Appl. Phys. Lett. 100, 262408 (2012); http://dx.doi.org/10.1063/1.4732083 (5 pages) | Cited 2 times

Online Publication Date: 28 June 2012

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We report experimentally obtained magnetic domain wall (DW) velocities of current-assisted field-driven DW creep in perpendicularly magnetized Pt/Co/Pt. We have intentionally introduced an asymmetry in the stacks by using different thicknesses of the two Pt layers sandwiching the Co layer. Thereby, it is tested whether conflicting current-induced domain wall motion (CI-DWM) results may be intrinsically related to the basic layout and growth. We sketch a scenario which could be at the basis of contradicting reports in literature where the direction of CI-DWM conflicts with spin-torque-transfer theory, allowing the sign of the current-induced effect on DW motion to be tuned.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ch Domain walls and domain structure
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Crystalline anisotropic magnetoresistance with two-fold and eight-fold symmetry in (In,Fe)As ferromagnetic semiconductor

Pham Nam Hai, Daisuke Sasaki, Le Duc Anh, and Masaaki Tanaka

Appl. Phys. Lett. 100, 262409 (2012); http://dx.doi.org/10.1063/1.4730955 (5 pages) | Cited 2 times

Online Publication Date: 28 June 2012

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We have investigated the anisotropic magnetoresistance (AMR) of (In,Fe)As ferromagnetic semiconductor layers grown on semi-insulating GaAs substrates. In a 10 nm-thick (In,Fe)As layer which is insulating at low temperature, we observed crystalline AMR with two-fold and eight-fold symmetries. In a metallic 100 nm-thick (In,Fe)As layer with higher electron concentration, only two-fold symmetric crystalline AMR was observed. Our results demonstrate the macroscopic ferromagnetism in (In,Fe)As with magnetic anisotropy that depends on the electron concentration. Very small (∼10−5) non-crystalline AMR is also observed in the 100 nm-thick layer, suggesting that there is no s-d scattering near the Fermi level of (In,Fe)As.
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75.70.Ak Magnetic properties of monolayers and thin films
75.75.Cd Fabrication of magnetic nanostructures
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
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