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7 Feb 2005

Volume 86, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 86, 063101 (2005); http://dx.doi.org/10.1063/1.1861133 (3 pages)

Choongho Yu, Qing Hao, Sanjoy Saha, Li Shi, Xiangyang Kong, and Z. L. Wang
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X-ray absorption spectroscopy in MnxGe1−x diluted magnetic semiconductor: Experiment and theory

S. Picozzi, L. Ottaviano, M. Passacantando, G. Profeta, A. Continenza, F. Priolo, M. Kim, and A. J. Freeman

Appl. Phys. Lett. 86, 062501 (2005); http://dx.doi.org/10.1063/1.1861127 (3 pages) | Cited 18 times

Online Publication Date: 31 January 2005

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Accurate first-principles calculations of soft x-ray absorption spectra are compared with experimental data obtained for the ion-implanted MnxGe1−x ferromagnetic semiconductor. The well-defined features in the spectra are recognized as a signature of homogeneous Mn dilution within the Ge host, as demonstrated by comparing the Mn spectra in diluted MnGe alloys with other competing Mn–Ge crystalline phases. Moreover, provided that an efficient Mn dilution is achieved, the nature of the semiconducting host is shown to affect only slightly the Mn absorption spectrum, as shown by the similarity of the present results with those for other magnetic semiconductors. Both these findings establish the relevance of ion-implantation in the dilute magnetic semiconductor framework, emphasizing its potential impact in device technology.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
78.70.Dm X-ray absorption spectra
78.40.Fy Semiconductors
61.72.S- Impurities in crystals

Enhanced magnetoresistance in strain-free manganite network

T. Wu and J. F. Mitchell

Appl. Phys. Lett. 86, 062502 (2005); http://dx.doi.org/10.1063/1.1861493 (3 pages) | Cited 12 times

Online Publication Date: 31 January 2005

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A network structure of a ferromagnetic metallic (FMM)∕charge-ordered insulator (COI) mixed phase manganite has been obtained by annealing a 150 Å Pr0.65(Ca0.75Sr0.25)0.35MnO3 film under tensile strain on a SrTiO3 substrate. Under the same deposition and annealing conditions, a film deposited on a LaAlO3 substrate, which provides compressive strain, remains continuous. The network structure also manifests a larger magnetoresistance than the continuous film. It is suggested that the lateral confinement in this filamentary structure may affect the percolative transport in this mixed FMM∕COI system.
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75.50.Dd Nonmetallic ferromagnetic materials
75.47.Lx Magnetic oxides
75.70.Ak Magnetic properties of monolayers and thin films
81.40.Rs Electrical and magnetic properties related to treatment conditions
68.55.-a Thin film structure and morphology
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.40.Gh Other heat and thermomechanical treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)

Easy axis alignment of chemically partially ordered FePt nanoparticles

Shishou Kang, Zhiyong Jia, Shifan Shi, David E. Nikles, and J. W. Harrell

Appl. Phys. Lett. 86, 062503 (2005); http://dx.doi.org/10.1063/1.1856698 (3 pages) | Cited 48 times

Online Publication Date: 31 January 2005

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Partially ordered Fe53Pt47 nanoparticles with size around 8 nm were prepared by the simultaneous decomposition of iron pentacarbonyl and platinum acetylacetonate. The high boiling point chemical, hexadecylamine, was used as a solvent, and 1-adamantanecarboxylic acid was used as a stabilizer. X-ray diffraction measurements reveal that as-made FePt particles were partially transformed into the ordered L10 phase with some weak superlattice peaks. The room-temperature hysteresis loop and remanence curve suggest a broad distribution of anisotropies in the partially ordered particles. By coating the partially ordered FePt nanoparticles with a polyvinylchloride polymer binder, the particles could be re-dispersed in cyclohexanone. Furthermore, the easy axis of the particles coated with the polyvinylchloride polymer binder could be aligned under an external field. Easy axis alignment was confirmed from both alternating gradient magnetometer and x-ray diffraction measurements.
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75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ww Permanent magnets
81.16.Be Chemical synthesis methods
81.05.Bx Metals, semimetals, and alloys
75.30.Gw Magnetic anisotropy
64.70.K- Solid-solid transitions
61.46.-w Structure of nanoscale materials

Electronic structure and magnetic properties of Al-doped Fe3O4 films studied by x-ray absorption and magnetic circular dichroism

C. K. Yang, J. W. Chiou, H. M. Tsai, C. W. Pao, J. C. Jan, S. C. Ray, C. L. Yeh, K. C. Huang, H. C. Hsueh, W. F. Pong, M.-H. Tsai, H. H. Hsieh, H. J. Lin, T. Y. Hou, and J. H. Hsu

Appl. Phys. Lett. 86, 062504 (2005); http://dx.doi.org/10.1063/1.1863450 (3 pages) | Cited 4 times

Online Publication Date: 1 February 2005

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The electronic structure and magnetic properties of Al-doped Fe3O4 films at various Al concentrations were investigated by Al and O K-edge x-ray absorption near-edge structure (XANES) and Fe L3,2-edge magnetic circular dichroism (MCD) measurements. The O K-edge XANES spectra reveal that the intensity of O 2p–Fe 3d hybridized states decreases linearly as the Al concentration increases, suggesting that nonmagnetic Al substitution reduces couplings of the O 2p with Fe 3d orbitals. The Fe L3-edge MCD spectra show that the intensities of MCD features decrease as the Al concentration increases, which suggests that Al substitution reduces the magnetic moments of Fe ions. The Fe L3,2 XANES spectra suggest the absence of mixed valence states in agreement with previous x-ray resonance scattering measurements.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
73.20.At Surface states, band structure, electron density of states
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Ht Other nonmetals
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
61.72.S- Impurities in crystals

Precharging strategy to accelerate spin-transfer switching below the nanosecond

T. Devolder, C. Chappert, P. Crozat, A. Tulapurkar, Y. Suzuki, J. Miltat, and K. Yagami

Appl. Phys. Lett. 86, 062505 (2005); http://dx.doi.org/10.1063/1.1853517 (3 pages) | Cited 25 times

Online Publication Date: 2 February 2005

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We compared different ways of inducing magnetization switching by spin momentum transfer in pillar shaped CoFe/Cu/CoFe trilayers using sub-ns-current pulses. In comparison with switching induced by a single sub-ns pulse, precharging the device with a bias current prior to the application of the pulse proved to lower the required peak current. Precharging is efficient for pulses ranging from 2 ns down to at least 200 ps. Simulations indicate that the bias current prepares the magnetization in a precession state that provides an enhanced susceptibility to the spin torque of the pulsed current. The precession settling time is typically 2 ns, hence the precharging strategy loses its efficiency for longer pulses, in agreement with experiments.
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75.50.Bb Fe and its alloys
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.47.De Giant magnetoresistance
75.40.Mg Numerical simulation studies

Observation of magnetization reversal in epitaxial Gd0.67Ca0.33MnO3 thin films

Yanwei Ma, M. Guilloux-Viry, P. Barahona, O. Peña, and C. Moure

Appl. Phys. Lett. 86, 062506 (2005); http://dx.doi.org/10.1063/1.1862787 (3 pages) | Cited 6 times

Online Publication Date: 3 February 2005

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High-quality epitaxial thin films ( ∼ 200 nm thick) of Gd0.67Ca0.33MnO3 have been deposited onto (100) SrTiO3 substrates by pulsed-laser deposition. Enhanced properties in comparison with bulk samples were observed. The magnetic transition temperature (Tc) of the as-grown films is much higher than the corresponding bulk values. Most interestingly, magnetization measurements performed under small applied fields, exhibit magnetization reversals below Tc, no matter whether the film is field cooled (FC) or zero-field cooled (ZFC). A rapid magnetization reversal occurs at 7 K when field cooled, while as for the ZFC process the magnetization decreases gradually with increasing temperatures, taking negative values above 7 K and changing to positive values again, above 83 K. In higher magnetic fields the magnetization does not change sign. The reversal mechanism is discussed in terms of a negative exchange f-d interaction and magnetic anisotropy, this later enhanced by strain effects induced by the lattice mismatch between the film and the substrate.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
68.55.-a Thin film structure and morphology
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Controlling magnetic moment and its fluctuations in individual semimagnetic quantum dots with different exchange interactions

P. S. Dorozhkin, V. D. Kulakovskii, A. V. Chernenko, A. S. Brichkin, S. V. Ivanov, and A. A. Toropov

Appl. Phys. Lett. 86, 062507 (2005); http://dx.doi.org/10.1063/1.1861954 (3 pages)

Online Publication Date: 4 February 2005

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The influence of exchange interaction between exciton and magnetic impurity spins on magnetic moment and its fluctuations in semimagnetic quantum dots has been investigated with the use of individual dot magnetophotoluminescence technique. In quantum dots with strong exchange interaction, both the polarization of magnetic ions and magnetic fluctuations in a dot are highly influenced by the formation of exciton magnetic polaron. In contrast, in the quantum dots with weak interaction, the localized exciton acts as a perfect noninvasive probe: it allows one to analyze the quantum-dot magnetic moment and its fluctuations with negligibly small influence on the dot magnetization. Numerical values of exchange magnetic field and magnetic polaron energy are obtained and analyzed for both types of dots.
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75.50.Pp Magnetic semiconductors
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
68.65.Ac Multilayers
73.21.La Quantum dots
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
75.30.Hx Magnetic impurity interactions
75.30.Ds Spin waves
78.55.Et II-VI semiconductors
71.38.-k Polarons and electron-phonon interactions
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