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19 Mar 2012

Volume 100, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 100, 121101 (2012); http://dx.doi.org/10.1063/1.3693413 (4 pages)

Jolly Xavier, Raktim Dasgupta, Sunita Ahlawat, Joby Joseph, and Pradeep Kumar Gupta
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Adjustable nitrogen-vacancy induced magnetism in AlN

Yu Liu, Liangbao Jiang, Gang Wang, Sibin Zuo, Wenjun Wang, and Xiaolong Chen

Appl. Phys. Lett. 100, 122401 (2012); http://dx.doi.org/10.1063/1.3696023 (3 pages) | Cited 5 times

Online Publication Date: 19 March 2012

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Nitrogen-vacancy-induced magnetism in AlN is investigated both theoretically and experimentally. First-principles calculations reveal that magnetic coupling between the vacancy-induced moments varies with the vacancy concentration. A sizable ferromagnetic coupling for nitrogen vacancies is found. Experimentally, the magnetism manipulation is realized accordingly by introducing vacancies through varying the nitrogen atmosphere in AlN whiskers. The vacancy control may be applicable to other III-V nitride semiconductors in tuning their magnetism.
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61.72.jd Vacancies
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Cr Saturation moments and magnetic susceptibilities
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)

Electrical control of Curie temperature in cobalt using an ionic liquid film

K. Shimamura, D. Chiba, S. Ono, S. Fukami, N. Ishiwata, M. Kawaguchi, K. Kobayashi, and T. Ono

Appl. Phys. Lett. 100, 122402 (2012); http://dx.doi.org/10.1063/1.3695160 (3 pages) | Cited 6 times

Online Publication Date: 19 March 2012

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The electric field effect on magnetization properties and Curie temperature of Co ultra-thin films has been investigated. An electric field is applied to a Co film by using an electric double layer (EDL) formed in a polymer film containing an ionic liquid. The change in the Curie temperature is ∼100 K by applying the gate voltage of ±2 V, suggesting that the observed large modifications of magnetization properties are attributed to the significant change in the Curie temperature, which is induced by a large amount of carrier density control due to the formation of the EDL.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
82.45.Mp Thin layers, films, monolayers, membranes
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.61.At Metal and metallic alloys

Magnetic properties of ZnFe2O4 ferrite nanoparticles embedded in ZnO matrix

N. Guskos, S. Glenis, G. Zolnierkiewicz, J. Typek, P. Berczynski, A. Guskos, D. Sibera, and U. Narkiewicz

Appl. Phys. Lett. 100, 122403 (2012); http://dx.doi.org/10.1063/1.3696024 (3 pages) | Cited 1 time

Online Publication Date: 20 March 2012

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Two magnetic nanocomposites were prepared from nanocrystalline zinc oxide doped with different concentrations of iron oxide (5 and 10 wt. %). X-ray diffraction and scanning electron microscopy have shown the growth of ZnFe2O4 nanocrystallites with size below 10 nm within the ZnO matrix in a highly agglomerated structure. Ferromagnetic resonance (FMR) measurements have shown line arising from the ZnFe2O4 nanoparticles. Temperature dependence of the FMR spectra parameters (amplitude, resonance field, linewidth, integrated intensity) has been investigated in the 4–300 K range. Zero-field cooled and field-cooled dc magnetic magnetization study in the same temperature range allowed to determine the blocking temperature TB and compare the results of two applied magnetic methods. Temperature dependence of FMR integrated intensity curve displays a peak at TB ∼ 23 K while FMR amplitude curve peaks at TC ∼ 170 K, the Curie-Weiss temperature of the high temperature susceptibility.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Pp Magnetic semiconductors
75.50.Gg Ferrimagnetics

Micromagnetic analysis of switching and domain structure in amorphous metallic nanowires

Laurentiu Stoleriu, Ciprian Pinzaru, and Alexandru Stancu

Appl. Phys. Lett. 100, 122404 (2012); http://dx.doi.org/10.1063/1.3696046 (4 pages) | Cited 1 time

Online Publication Date: 20 March 2012

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This paper describes a comprehensive micromagnetic model for the observed complex magnetic domains structures in amorphous wires with positive and negative magnetostriction with or without a glass cover. Many experimental studies and theoretical analysis have suggested several typical domain structures. We show the results of micromagnetic simulations that cover many of these observed data using a single set of physical hypotheses.
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75.60.Ch Domain walls and domain structure
81.07.Gf Nanowires
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.78.Cd Micromagnetic simulations
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction
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Electric field effects in low resistance CoFeB-MgO magnetic tunnel junctions with perpendicular anisotropy

H. Meng, R. Sbiaa, M. A. K. Akhtar, R. S. Liu, V. B. Naik, and C. C. Wang

Appl. Phys. Lett. 100, 122405 (2012); http://dx.doi.org/10.1063/1.3695168 (3 pages) | Cited 8 times

Online Publication Date: 20 March 2012

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We have investigated the electric field effects in low resistance perpendicular magnetic tunnel junction (MTJ) devices and found that the electric field can effectively reduce the coercivity (Hc) of free layer (FL) by 30% for a bias voltage Vb = −0.2 V. In addition, the bias field (Hb) on free layer is almost linearly dependent on Vb yet independent on the device size. The demonstrated Vb dependences of Hc and Hb in low resistance MTJ devices present the potential to extend the scalability of the electric field assisted spin transfer torque magnetic random access memory and improve its access speed.
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85.75.Dd Magnetic memory using magnetic tunnel junctions
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices

Long-lived, room-temperature electron spin coherence in colloidal CdS quantum dots

D. H. Feng, X. Li, T. Q. Jia, X. Q. Pan, Z. R. Sun, and Z. Z. Xu

Appl. Phys. Lett. 100, 122406 (2012); http://dx.doi.org/10.1063/1.3696069 (4 pages) | Cited 2 times

Online Publication Date: 21 March 2012

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Time-resolved Faraday rotation spectroscopy is used to study the electron spin coherence in colloidal CdS quantum dots. Long-lived spin coherence with dephasing time T2*>3ns has been found at room temperature. Spin dynamics unaffected by the faster carrier recombination suggests the spin signal coming from the residual electrons in the dots. A small external transverse magnetic field of 50 mT can extend T2* ∼ 2 times longer compared with that in zero magnetic field. Hyperfine interaction between electron and nuclear spins limits the dephasing time in zero or low magnetic field, while for higher magnetic fields, inhomogeneous dephasing becomes to dominate the spin dynamics.
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78.67.Hc Quantum dots
78.20.Ls Magneto-optical effects
78.47.D- Time resolved spectroscopy (>1 psec)
82.70.Dd Colloids
71.70.Jp Nuclear states and interactions

Mechanically tunable magnetic properties of Fe81Ga19 films grown on flexible substrates

Guohong Dai, Qingfeng Zhan, Yiwei Liu, Huali Yang, Xiaoshan Zhang, Bin Chen, and Run-Wei Li

Appl. Phys. Lett. 100, 122407 (2012); http://dx.doi.org/10.1063/1.3696887 (4 pages) | Cited 2 times

Online Publication Date: 21 March 2012

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We investigated on magnetic properties of magnetostrictive Fe81Ga19 films grown on flexible polyethylene terephthalate (PET) substrates under various mechanical strains. The unstrained Fe81Ga19 films exhibit a significant uniaxial magnetic anisotropy due to a residual stress in PET substrates. It was found that the squareness of hysteresis loops can be tuned by an application of strains, inward/compressive or outward/tensile bending of the films. A modified Stoner-Wohlfarth model with considering a distribution of easy axes in polycrystalline films was developed to account for the mechanically tunable magnetic properties in flexible Fe81Ga19 films. These results provide an alternative way to tune mechanically magnetic properties, which is particularly important for developing flexible magnetoelectronic devices.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.80.+q Magnetomechanical effects, magnetostriction
81.05.Bx Metals, semimetals, and alloys
81.15.Cd Deposition by sputtering
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Breakdown by magnetic field in a La0.7Sr0.3MnO3/MgO/Fe spin valve

Xiaojie Wu, Zhenzhong Zhang, and Jian Meng

Appl. Phys. Lett. 100, 122408 (2012); http://dx.doi.org/10.1063/1.3696670 (3 pages)

Online Publication Date: 22 March 2012

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A La0.7Sr0.3MnO3/MgO/Fe spin valve with inverse tunneling magnetoresistance (TMR) was fabricated on a (100) SrTiO3 substrate by radio frequency magnetron sputtering. Giant TMR ratios up to 540% were obtained. The breakdown of the spin valve was observed at high magnetic field, which was attributed to the joint action of the invalidation of MgO barrier and the shift of Fermi energy in La0.7Sr0.3MnO3 at high magnetic field.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
81.15.Cd Deposition by sputtering

Tailoring interfacial exchange coupling with low-energy ion beam bombardment: Tuning the interface roughness

K.-W. Lin, M. Mirza, C. Shueh, H.-R. Huang, H.-F. Hsu, and J. van Lierop

Appl. Phys. Lett. 100, 122409 (2012); http://dx.doi.org/10.1063/1.3697405 (4 pages) | Cited 7 times

Online Publication Date: 22 March 2012

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By ascertaining NiO surface roughness in a Ni80Fe20/NiO film system, we were able to correlate the effects of altered interface roughness from low-energy ion-beam bombardment of the NiO layer and the different thermal instabilities in the NiO nanocrystallites. From experiment and by modelling the temperature dependence of the exchange bias field and coercivity, we have found that reducing the interface roughness and changing the interface texture from an irregular to striped conformation enhanced the exchange coupling strength. Our results were in good agreement with recent simulations using the domain state model that incorporated interface mixing.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
61.80.Jh Ion radiation effects
68.35.Ct Interface structure and roughness

Manipulation of magnetic anisotropy of Fe/graphene by charge injection

S. J. Gong, Chun-Gang Duan, Zi-Qiang Zhu, and Jun-Hao Chu

Appl. Phys. Lett. 100, 122410 (2012); http://dx.doi.org/10.1063/1.3697627 (3 pages) | Cited 2 times

Online Publication Date: 23 March 2012

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We propose that charge injection can be used to tune the magnetic anisotropy of transition metal monolayer adsorbed on graphene substrate. Using relativistic density-functional calculations, we calculate magnetocrystalline anisotropy energy (MAE) of freestanding Fe monolayer and Fe/graphene complex system. We find MAE of Fe atom is drastically changed, from meV/atom in freestanding Fe monolayer to μeV/atom in Fe/graphene system. The more interesting finding is, through charge injection, the suppressed MAE of Fe atoms in Fe/graphene system can be restored back, which provides an effective approach to control MAE. We expect such strategy would be beneficial to graphene based spintronic devices.
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75.30.Gw Magnetic anisotropy
68.43.Mn Adsorption kinetics
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
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