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3 Sep 2012

Volume 101, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 101, 103101 (2012); http://dx.doi.org/10.1063/1.4748099 (5 pages)

Massimo Cuscunà, Annalisa Convertino, Emiliano Zampetti, Antonella Macagnano, Alessandro Pecora, Guglielmo Fortunato, Laura Felisari, Giuseppe Nicotra, Corrado Spinella, and Faustino Martelli
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Observation of a 0.5 conductance plateau in asymmetrically biased GaAs quantum point contact

N. Bhandari, P. P. Das, M. Cahay, R. S. Newrock, and S. T. Herbert

Appl. Phys. Lett. 101, 102401 (2012); http://dx.doi.org/10.1063/1.4749817 (4 pages) | Cited 3 times

Online Publication Date: 4 September 2012

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We report the observation of a robust anomalous conductance plateau near G = 0.5 G0 (G0 = 2e2/h) in asymmetrically biased AlGaAs/GaAs quantum point contacts (QPCs), with in-plane side gates in the presence of lateral spin-orbit coupling. This is interpreted as evidence of spin polarization in the narrow portion of the QPC. The appearance and evolution of the conductance anomaly has been studied at T = 4.2 K as a function of the potential asymmetry between the side gates. Because GaAs is a material with established processing techniques, high mobility, and a relatively high spin coherence length, the observation of spontaneous spin polarization in a side-gated GaAs QPC could eventually lead to the realization of an all-electric spin-valve at tens of degrees Kelvin.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.25.-b Spin polarized transport
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Unusual lattice constant changes and tunable magnetic moment compensation in Mn50−xCo25Ga25+x alloys

G. J. Li, E. K. Liu, H. G. Zhang, J. F. Qian, H. W. Zhang, J. L. Chen, W. H. Wang, and G. H. Wu

Appl. Phys. Lett. 101, 102402 (2012); http://dx.doi.org/10.1063/1.4749837 (4 pages) | Cited 2 times

Online Publication Date: 4 September 2012

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We report on unusual lattice parameter changes and tunable magnetic moment compensation in Mn50−xCo25Ga25+x (x = 0-25) Heusler alloys by substituting Ga for Mn. The observed lattice parameter first increases with increasing Ga content x, showing a maximum at x = 12.5, and then abnormally decreases due to the enhanced covalence effect between transition-metal and main-group atoms. Moreover, a tunable magnetic moment compensation was also observed due to the diversification in role of the main magnetic contributor when the structure varies from Hg2CuTi-type Mn2CoGa to Cu2MnAl-type CoMnGa2. These results provide an alternative way to simultaneously tune both the structural and magnetic properties of Heusler alloys, which is particularly important for developing flexible spintronics devices.
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61.66.Dk Alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

The magnetic Y-branch nanojunction: Domain-wall structure and magneto-resistance

Z. Chen, T.-Y. Lin, X. Wei, M. Matsunaga, T. Doi, Y. Ochiai, N. Aoki, and J. P. Bird

Appl. Phys. Lett. 101, 102403 (2012); http://dx.doi.org/10.1063/1.4750240 (5 pages)

Online Publication Date: 4 September 2012

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We analyze the domain structure of magnetic Y-branch nanojunctions that are formed by the intersection of a pair of orthogonal nanoscale notches. Dependent upon the magnetization history, we show the possibility of localizing various domain-wall (DW) structures at different parts of these junctions, leading to measurable magneto-resistance changes. These changes in turn allow the investigation of DW resistance, separate from the complicating effects of anisotropic magneto-resistance. The capacity to electrically detect the presence of DW structures in different regions of the junction may eventually make these structures of interest for future investigations of DW-enabled logic.
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75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms
75.75.Fk Domain structures in nanoparticles
75.47.-m Magnetotransport phenomena; materials for magnetotransport
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C60-based hot-electron magnetic tunnel transistor

M. Gobbi, A. Bedoya-Pinto, F. Golmar, R. Llopis, F. Casanova, and L. E. Hueso

Appl. Phys. Lett. 101, 102404 (2012); http://dx.doi.org/10.1063/1.4751030 (4 pages) | Cited 1 time

Online Publication Date: 4 September 2012

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A C60-based magnetic tunnel transistor is presented. The device is based on the collection of spin-filtered hot-electrons at a metal/C60 interface, and it allows an accurate measurement of the energy level alignment at such interface. A 89% change in the collected current under the application of a magnetic field demonstrates that these devices can be used as sensitive magnetic field sensors compatible with soft electronics.
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85.30.Tv Field effect devices

The spin-filter capability and spin-reversal effect of multidecker iron-borazine sandwich cluster

Zhi Yang, Shaoding Liu, Xuguang Liu, Yongzhen Yang, Xiuyan Li, Shijie Xiong, and Bingshe Xu

Appl. Phys. Lett. 101, 102405 (2012); http://dx.doi.org/10.1063/1.4751340 (4 pages)

Online Publication Date: 5 September 2012

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Using density functional theory and non-equilibrium Green's function technique, we performed theoretical investigations on the magnetic and transport properties of Fen(B3N3H6)n+1 (n = 1-4) sandwich clusters. The calculated results show that the clusters possess high magnetic moments owing to the unpaired dδ electrons. Furthermore, high spin-filter capability, negative differential resistance, and spin-reversal effect were found in the systems, and the possible physical origination of the phenomena was suggested. Our findings also indicate that the magnetic or electrical properties of the system could be controlled by cluster size, and these sandwich clusters are promising materials for application in molecular electronics or spintronics.
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73.40.Rw Metal-insulator-metal structures
75.30.Cr Saturation moments and magnetic susceptibilities

Pulse voltage-induced dynamic magnetization switching in magnetic tunneling junctions with high resistance-area product

Yoichi Shiota, Shinji Miwa, Takayuki Nozaki, Frédéric Bonell, Norikazu Mizuochi, Teruya Shinjo, Hitoshi Kubota, Shinji Yuasa, and Yoshishige Suzuki

Appl. Phys. Lett. 101, 102406 (2012); http://dx.doi.org/10.1063/1.4751035 (4 pages) | Cited 2 times

Online Publication Date: 5 September 2012

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We investigated pulse voltage-induced dynamic magnetization switchings in magnetic tunneling junctions with a high resistance-area product of 2 kΩ μm2. We found that bistable switching and the oscillatory behavior of switching probability as a function of voltage pulse duration are realized at a lower current density (−1.1 × 105 A/cm2) than in conventional spin-transfer-torque-induced magnetization switching. In addition, the switching probability at different voltage pulse strengths confirmed the existence of a voltage torque induced by a change in perpendicular magnetic anisotropy. This voltage-induced magnetization switching can be a useful technique in future spintronics devices with fast and highly reliable writing processes.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.78.Jp Ultrafast magnetization dynamics and switching

Excellent magnetocaloric properties of melt-extracted Gd-based amorphous microwires

N. S. Bingham, H. Wang, F. Qin, H. X. Peng, J. F. Sun, V. Franco, H. Srikanth, and M. H. Phan

Appl. Phys. Lett. 101, 102407 (2012); http://dx.doi.org/10.1063/1.4751038 (5 pages)

Online Publication Date: 6 September 2012

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We report upon the excellent magnetocaloric properties of Gd53Al24Co20Zr3 amorphous microwires. In addition to obtaining the large magnetic entropy change (−ΔSM ∼ 10.3 J/kg K at TC ∼ 95 K), an extremely large value of refrigerant capacity (RC ∼ 733.4 J/kg) has been achieved for a field change of 5 T in an array of forty microwires arranged in parallel. This value of RC is about 79% and 103% larger than those of Gd (∼410 J/kg) and Gd5Si2Ge1.9Fe0.1 (∼360 J/kg) regardless of their magnetic ordering temperatures. The design and fabrication of a magnetic bed made of these parallel-arranged microwires would thus be a very promising approach for active magnetic refrigeration for nitrogen liquefaction. Since these microwires can easily be assembled as laminate structures, they have potential applications as a cooling device for micro electro mechanical systems and nano electro mechanical systems.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.05.Bx Metals, semimetals, and alloys
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Giant induced magnetic anisotropy In strain annealed Co-based nanocomposite alloys

Samuel J. Kernion, Paul. R. Ohodnicki, Jr., Jane Grossmann, Alex Leary, Shen Shen, Vladimir Keylin, Joseph F. Huth, John Horwath, Matthew S. Lucas, and Michael E. McHenry

Appl. Phys. Lett. 101, 102408 (2012); http://dx.doi.org/10.1063/1.4751253 (5 pages) | Cited 3 times

Online Publication Date: 6 September 2012

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Low loss switching of soft magnetic materials at high frequencies benefits from tuning the induced anisotropy. We show induced anisotropies, Ku, as large as 1.89×104 J/m3, developed by strain annealing of Co-rich nanocomposite alloys. Crystalline phases in this alloy system have large negative magnetostrictive coefficients, leading to anisotropy fields per unit stress over twice those developed in FINEMET. Tunable permeability and reduced thicknesses achieved in this process can mitigate eddy-current losses. Giant induced magnetic anisotropies are discussed in light of models for the micromechanisms of amorphous metal deformation, stress-assisted transformations in the crystallites, and directional pair ordering.
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75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
81.40.Gh Other heat and thermomechanical treatments
64.70.K- Solid-solid transitions
75.60.-d Domain effects, magnetization curves, and hysteresis
75.80.+q Magnetomechanical effects, magnetostriction

Magnetic and transport properties of layered LixCo0.5RhO3

Tsuyoshi Takami, Jinguang Cheng, and John B. Goodenough

Appl. Phys. Lett. 101, 102409 (2012); http://dx.doi.org/10.1063/1.4751337 (3 pages)

Online Publication Date: 7 September 2012

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Band insulator Li1.5Co0.5RhO3 has been synthesized, in which Co and Rh atoms are partially disordered in the two-dimensional Co1/3Rh2/3O2 layer. Measurements of magnetic susceptibility indicate that Co(III) and Co(III) are both diamagnetic with low-spin configurations. The electrical resistivity and thermopower reveal one-dimensional variable-range hopping below T1 = 320 K and above T2 = 630 K. Charges introduced by Li extraction down to x = 0.75 in LixCo0.5RhO3 yield the systematic decreases in resistivity and T1, but the magnetic ordering is observed at TN = 30 K, which can be accounted for by spin-orbital coupling with antiferromagnetic interaction.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.20.Ck Nonmetals
72.20.Pa Thermoelectric and thermomagnetic effects
72.20.Ee Mobility edges; hopping transport
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.50.Ee Antiferromagnetics

The effect of interfaces on magnetic activation volumes in single crystal Co2FeSi Heusler alloy thin films

J. Sagar, H. Sukegawa, L. Lari, V. K. Lazarov, S. Mitani, K. O'Grady, and A. Hirohata

Appl. Phys. Lett. 101, 102410 (2012); http://dx.doi.org/10.1063/1.4749822 (4 pages) | Cited 1 time

Online Publication Date: 7 September 2012

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Structural and magnetization reversal studies have been carried out on single crystal Co2FeSi thin films grown on MgO (001) substrates. The films are highly L21 ordered after annealing above 500 °C. Magnetization reversal has been investigated by measurements of the activation volumes (Vact) within the films. This volume represents the unit of reversal in a magnetic material. Vact (∼4 × 103 nm3) has been found to be independent of the physical structure. Vact is found to correspond to an array of periodic misfit dislocations at the Co2FeSi/MgO interface. Such a small Vact potentially prevents coherent magnetization reversal as required for giant magnetoresistance or tunnel magnetoresistance devices.
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68.55.-a Thin film structure and morphology
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments

Positive and negative exchange bias effects in the simple perovskite manganite NdMnO3

Fang Hong, Zhenxiang Cheng, Jianli Wang, Xiaolin Wang, and Shixue Dou

Appl. Phys. Lett. 101, 102411 (2012); http://dx.doi.org/10.1063/1.4751990 (5 pages)

Online Publication Date: 7 September 2012

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Exchange bias effects were studied in the simple perovskite NdMnO3. Nd3+ ordering is induced by the Mn3+ ferromagnetic component, and they are antiferromagnetically coupled with each other. At 30 K, both negative and positive exchange bias effects are found, which are dependent on the cooling field. The exchange bias fields are around −2400 Oe and 1800 Oe, respectively. Positive and negative exchange bias effects were also observed at 8 K, but the exchange bias fields are only 130 Oe and −120 Oe. The coupling intensity between Nd3+ ordering and Mn3+ ordering, and their initial states determine the polarity of the exchange bias fields.
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75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics

Observation of spin-polarized electron transport in Alq3 by using a low work function metal

Hyuk-Jae Jang, Kurt P. Pernstich, David J. Gundlach, Oana D. Jurchescu, and Curt. A. Richter

Appl. Phys. Lett. 101, 102412 (2012); http://dx.doi.org/10.1063/1.4751257 (5 pages)

Online Publication Date: 7 September 2012

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We present the observation of magnetoresistance in Co/Ca/Alq3/Ca/NiFe spin-valve devices. Thin Ca layers contacting 150 nm thick Alq3 enable the injection of spin-polarized electrons into Alq3 due to the engineering of the band alignment. The devices exhibit symmetric current-voltage (I–V) characteristics indicating identical metal contacts on Alq3, and up to 4% of positive magnetoresistance was observed at 4.5 K. In contrast, simultaneously fabricated Co/Alq3/NiFe devices displayed asymmetric I–V curves due to the different metal electrodes, and spin-valve effects were not observed.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
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