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7 May 2013

Volume 113, Issue 17, Articles (17xxxx)

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J. Appl. Phys. 113, 174302 (2013); http://dx.doi.org/10.1063/1.4798262 (4 pages)

Yuichiro Kurokawa, Takehiko Hihara, and Ikuo Ichinose
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back to top Magnetic Semiconductors

Non-volatile, reversible switching of the magnetic moment in Mn-doped ZnO films

X. L. Wang, Q. Shao, C. W. Leung, and A. Ruotolo

J. Appl. Phys. 113, 17C301 (2013); http://dx.doi.org/10.1063/1.4793639 (3 pages)

Online Publication Date: 27 February 2013

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We report on the observation of a non-volatile, reversible switching of the magnetic moment in Mn-doped ZnO thin films. The system is a typical oxide memristor based on an oxygen-deficient semiconductor oxide. In the present study, the oxide semiconductor is ferromagnetic at room temperature. We found that the bistable switching of the resistive state was accompanied by a bistable switching of the magnetic moment at room temperature. Our results support the hypothesis that ferromagnetism in Mn-doped ZnO is mediated by oxygen-vacancies.
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73.61.Ga II-VI semiconductors
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
75.30.Cr Saturation moments and magnetic susceptibilities
61.72.jd Vacancies

Correlation between magnetism and electronic structure of Zn1−xCoxO nanoparticles

Jordan Chess, Gordon Alanko, Dmitri A. Tenne, Charles B. Hanna, and Alex Punnoose

J. Appl. Phys. 113, 17C302 (2013); http://dx.doi.org/10.1063/1.4794355 (3 pages)

Online Publication Date: 11 March 2013

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Zn1−xCoxO nanoparticles (∼9 nm) were produced with x ranging from 0 to 0.2 using a forced hydrolysis method. X-ray diffraction measurements confirm the samples to be single phase, and reveal a systematic change in the lattice parameters upon cobalt doping. The unit cell volume V decreases up to x = 0.025 after which it stays roughly constant. The band gap energy (Eg), determined from the photoluminescence spectra gradually increases from x = 0 to 0.025 and then remains nearly constant for x > 0.025. Room temperature hysteresis loops, obtained using vibrating sample magnetometry, show a similar trend in the saturation magnetization (Ms). Undoped ZnO nanoparticles show a weak magnetic hysteresis; doping causes an increase in Ms up to x = 0.025 and then decreases to lower values for x > 0.025. The magnetic moment per Co ion μ decreases rapidly with x nearly following μ(x) ∝ 1/x, indicating that the moments from the Co ions have little impact on the observed magnetic properties. Electron paramagnetic resonance (EPR) data confirmed that the pure samples are free of any magnetic impurities, while all the doped samples show spectra corresponding to Co2+. The variation of the integrated EPR signal intensity with x also shows a maximum at x = 0.025. X-ray photoelectron spectroscopy confirm that the dopant is incorporated as high spin Co2+ ions for low x, but increasing fractions of the dopant ions change to Co3+ as x increases to 0.2. These results along with the strong correlation observed between the structural (V), electronic (Eg), and magnetic (Ms) properties of Zn1−xCoxO nanoparticles, and the rapid decrease in magnetic moment with increasing x, indicate that the observed changes in the magnetic properties are related to changes in the electronic structure of ZnO nanoparticles caused by dopant incorporation.
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75.75.Lf Electronic structure of magnetic nanoparticles
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.55.Et II-VI semiconductors
61.72.uj III-V and II-VI semiconductors

Fabrication of ferrimagnetic FeOx thin film and the resistance switching of Au/FeOx/Pt heterostructure

C. Yun, X. G. Chen, J. B. Fu, C. S. Wang, H. L. Du, G. C. Xiong, G. J. Lian, Y. C. Yang, and J. B. Yang

J. Appl. Phys. 113, 17C303 (2013); http://dx.doi.org/10.1063/1.4794138 (3 pages)

Online Publication Date: 12 March 2013

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By controlling the temperature and oxygen partial pressure, well polycrystalline Fe3O4 thin film on Pt substrate was fabricated, using a stoichiometric α-Fe2O3 target. A ferrimagnetic hysteresis loop and a Verwey transition at about 130 K were shown in the results of magnetic measurement. A sharp hysteretic resistance switching below Verwey transition temperature (Tv) was observed in I-V tests of the Au/Fe3O4/Pt heterostructure. Enlarged hysteresis by larger pulse delay and suppressed metal-insulator transition by larger source currents indicated that enhanced local Joule heating effect played an important role in the hysteresis of resistance switching.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Gh Other heat and thermomechanical treatments
72.60.+g Mixed conductivity and conductivity transitions
73.40.Ns Metal-nonmetal contacts
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic anisotropy in the boron nitride monolayer doped by 3d transitional metal substitutes at boron-site

Yuan Lu, Xu Zuo, Min Feng, and Tiege Zhou

J. Appl. Phys. 113, 17C304 (2013); http://dx.doi.org/10.1063/1.4798478 (3 pages)

Online Publication Date: 29 March 2013

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Based on density functional theory with the generalized gradient approximation, a computational study is carried out to reveal the magnetism of the hexagonal boron nitride monolayers (h-BN) doped by 3d transitional metal atoms at boron-site. The magnetic moments and magnetic anisotropy energies (MAEs) of the most stable structures are given. Among the systems investigated, the MAE of Fe doped h-BN is 1.19 meV with an easy axis in the h-BN plane, while that of Mn is 0.63 meV with an easy axis perpendicular to the plane. For Sc and Co, the doped systems are nonmagnetic. For Ti, V, Cr, Ni, Cu, and Zn, the MAEs are relatively small. Theoretical analyses by perturbation theory and molecular orbital clarify that the MAE of Fe originates from the second order spin orbit coupling, whereas the MAE of Mn is contributed by the unquenched orbital momentum.
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75.30.Gw Magnetic anisotropy
81.05.Ea III-V semiconductors
61.72.uj III-V and II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Nr Semiconductor compounds
75.30.Cr Saturation moments and magnetic susceptibilities

Model for Mn in 6H-SiC from first-principle studies

M. Al Azri, M. Elzain, K. Bouziane, S. M. Chérif, A. Declémy, and L. Thomé

J. Appl. Phys. 113, 17C305 (2013); http://dx.doi.org/10.1063/1.4798481 (3 pages)

Online Publication Date: 4 April 2013

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The electronic and magnetic properties of 6H-SiC with Mn impurities have been calculated using generalized gradient approximation formalism. Various configurations of Mn sites and Si and C vacancies were considered. It was found that 6H-SiC doped with Mn atoms possess a moment for both types of substitution. The Mn atom at Si site possesses larger magnetic moment than Mn atom at C site. The energy levels appearing in the band gap due to vacancies and due to Mn impurities are determined and the calculated densities of states are used to analyze the different values of the magnetic moments for different types of substitution. A model that explains the magnetic moment at Mn site is proposed.
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71.20.Nr Semiconductor compounds
61.72.jd Vacancies
61.72.U- Doping and impurity implantation

Formation and ferromagnetic properties of FeSi thin films

Yooleemi Shin, Duong Anh Tuan, Younghun Hwang, Tran Viet Cuong, and Sunglae Cho

J. Appl. Phys. 113, 17C306 (2013); http://dx.doi.org/10.1063/1.4800839 (3 pages)

Online Publication Date: 10 April 2013

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In this work, the growth and ferromagnetic properties of ε-FeSi thin film on Si(100) substrate prepared by molecular beam epitaxy are reported. The inter-diffusion of Fe layer on Si(100) substrate at 600 °C results in polycrystalline ε-FeSi layer. The determined activation energy was 0.044 eV. The modified magnetism from paramagnetic in bulk to ferromagnetic states in ε-FeSi thin films was observed. The saturated magnetization and coercive field of ε-FeSi film are 4.6 emu/cm3 and 29 Oe at 300 K, respectively.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
66.30.Ny Chemical interdiffusion; diffusion barriers
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
81.05.Bx Metals, semimetals, and alloys

Effect of growth temperature on magnetic and electronic properties of epitaxially grown MnAs thin films on GaAs(100) substrates

J. H. Song, Y. Cui, and J. B. Ketterson

J. Appl. Phys. 113, 17C307 (2013); http://dx.doi.org/10.1063/1.4801508 (3 pages)

Online Publication Date: 11 April 2013

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We grew epitaxial MnAs thin films on GaAs(100) substrates using molecular-beam epitaxy and investigated the growth temperature dependences of their physical properties. With increasing growth temperature from 200 °C to 350 °C, the crystal orientation of the film changed from type-A to type-B. The Curie temperatures of all type-B samples were ∼346 K, while the type-A sample showed a lower bulk-like value of ∼318 K, indicating an improvement in magnetic properties. Samples grown at above 550 °C exhibited semiconducting behavior, whereas the lower temperature grown samples show metallic behavior as expected. Our results indicate that growth temperature plays an important role in determining the crystal structure, magnetic, and electrical-transport properties of MnAs/GaAs(100) thin films.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.70.Ak Magnetic properties of monolayers and thin films
68.55.at Other materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
72.25.-b Spin polarized transport
73.61.Le Other inorganic semiconductors

Magnetic properties of Fe doped, Co doped, and Fe+Co co-doped ZnO

J. J. Beltrán, J. A. Osorio, C. A. Barrero, C. B. Hanna, and A. Punnoose

J. Appl. Phys. 113, 17C308 (2013); http://dx.doi.org/10.1063/1.4799778 (3 pages)

Online Publication Date: 16 April 2013

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The structural, electronic, and magnetic properties of Zn0.95Co0.05O, Zn0.95Fe0.05O, and Zn0.90Fe0.05Co0.05O nanoparticles prepared by a sol-gel method are presented and discussed. X-ray diffraction and optical analysis indicated that high spin Co2+ ions substitute for the Zn2+ ions in tetrahedral sites. 57Fe Mössbauer spectroscopy showed the presence of isolated paramagnetic Fe3+ ions in both Fe doped and Fe+Co co-doped ZnO, however, no evidence of ferromagnetically ordered Fe3+ ions is observed. In the Zn0.95Fe0.05O sample, weak presence of ZnFe2O4 was detected as an impurity phase, whereas Zn0.90Fe0.05Co0.05O was impurity-free within detection limit in all those measurements. Results of these studies suggest that Fe and Co ions in the Fe+Co co-doped sample has a strong synergistic effect because they eliminated the presence of impurities and gave the strongest ferromagnetic signal. Possible role of charge transfer ferromagnetism involving mixed valence ions is considered as a potential mechanism in these nanoparticles. Presence of both Co2+ and Fe3+ might promote more efficient charge transfer in the co-doped Zn0.90Fe0.05Co0.05O, leading to the enhanced ferromagnetism observed in this sample. However, more evidence is necessary to confirm the role of charge transfer ferromagnetism.
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75.75.Cd Fabrication of magnetic nanostructures
81.07.Bc Nanocrystalline materials
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena
73.22.-f Electronic structure of nanoscale materials and related systems

Ferromagnetism in cluster free, transition metal doped high κ dilute magnetic oxides: Films and nanocrystals

C. N. Wu, T. S. Wu, S. Y. Huang, W. C. Lee, Y. H. Chang, Y. L. Soo, M. Hong, and J. Kwo

J. Appl. Phys. 113, 17C309 (2013); http://dx.doi.org/10.1063/1.4799613 (3 pages)

Online Publication Date: 22 April 2013

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The structural and magnetic properties of high κ dilute magnetic oxides (DMOs) have been studied in two types of samples: thin films and nanocrystals, including Co doped HfO2 films, Co doped Y2O3 films, Co doped Y2O3 nanocrystals, and Mn doped Y2O3 nanocrystals. The characterizations were conducted by extended x-ray absorption fine structure, x-ray absorption near edge structure, and superconducting quantum interference device vibrating sample magnetometer. Oxygen vacancies are shown to play a crucial role in ferromagnetic ordering, as defect centers in the bound magnetic polaron model to account for DMOs with medium band gap and low carrier concentration. The observation of room temperature ferromagnetism in tri-valence oxide of Y2O3 as well as in tetra-valence oxide of HfO2 suggests a generic feature of transition metal doped high κ oxides as good candidates for DMO. The ability to modulate the magnetic behavior of DMO via oxygen vacancy concentration by means of post anneals can be exploited for potential applications in spintronics.
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61.46.Hk Nanocrystals
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.-c Magnetic properties of nanostructures
75.70.Ak Magnetic properties of monolayers and thin films
72.20.Fr Low-field transport and mobility; piezoresistance
71.38.-k Polarons and electron-phonon interactions
78.70.Dm X-ray absorption spectra
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