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10 May 2004

Volume 84, Issue 19, pp. 3723-3937

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 3933 (2004); http://dx.doi.org/10.1063/1.1745103 (3 pages)

A. Cassinese, G. M. De Luca, A. Prigiobbo, M. Salluzzo, and R. Vaglio
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Comparison of predicted ferromagnetic tendencies of Mn substituting the Ga site in III–V’s and in I–III–VI2 chalcopyrite semiconductors

Yu-Jun Zhao, Priya Mahadevan, and Alex Zunger

Appl. Phys. Lett. 84, 3753 (2004); http://dx.doi.org/10.1063/1.1737466 (3 pages) | Cited 10 times

Online Publication Date: 29 April 2004

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We report density-functional calculations of the ferromagnetic (FM) stabilization energy δ = EFM−EAFM for differently oriented Mn pairs in III–V’s (GaN, GaP, GaAs) and chalcopyrite (CuGaS2, CuGaSe2, CuGaTe2) semiconductors. Ferromagnetism is found to be the universal ground state (δ<0) in all cases. The order of FM stability in III–V’s is GaN>GaP>GaAs, whereas in chalcopyrites it is CuGaS2>CuGaSe2>CuGaTe2. Considering both groups, the order is GaN→GaP→GaAs→CuGaS2→CuGaSe2→GaSb ≈ CuGaTe2. The stronger FM stabilization in III–V’s is attributed to the stronger covalent coupling between the Mn 3d and the anion p orbitals. In contrast to expectations based on Ruderman–Kittel–(Kasuya)–Yosida, (i) all Mn–Mn pair separations show FM, with no FM to antiferromagnetic oscillations and, (ii) FM is orientationally dependent, with 〈110〉 Mn–Mn pairs being the most FM. © 2004 American Institute of Physics.
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71.20.Nr Semiconductor compounds
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Exchange bias of antiferromagnets with random anisotropies and perfectly compensated interfaces

T. Mewes and R. L. Stamps

Appl. Phys. Lett. 84, 3840 (2004); http://dx.doi.org/10.1063/1.1745112 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2004

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An alternative mechanism for exchange bias for ferromagnet/antiferromagnet bilayers with completely compensated interfaces is proposed and analyzed within the biquadratic coupling model. We show that a distribution of anisotropies in the antiferromagnet can lead to the appearance of exchange bias in a bilayer with a perfectly compensated interface without defects. The energy associated with the unidirectional anisotropy that gives rise to the shifted hysteresis curve is stored in antiferromagnetic domain walls between regions in the antiferromagnet with different anisotropy. This mechanism also leads naturally to an enhanced coercivity of the ferromagnet which is caused by the anisotropy in the antiferromagnet. © 2004 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Ee Antiferromagnetics
75.30.Et Exchange and superexchange interactions

Spin-transfer-induced precessional magnetization reversal

A. D. Kent, B. Özyilmaz, and E. del Barco

Appl. Phys. Lett. 84, 3897 (2004); http://dx.doi.org/10.1063/1.1739271 (3 pages) | Cited 35 times

Online Publication Date: 29 April 2004

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A magnetoelectronic device is proposed in which a spin-current pulse produces a rapid reversal of the magnetization of a thin film nanomagnet. A spin-transfer torque induces the reversal and the switching speed is determined by the precession frequency of the magnetization in a thin film element’s demagnetization field. Micromagnetic simulations show that this switching occurs above a threshold pulse current and can be faster than 50 ps. In contrast to present spin-transfer devices, the switching does not require an initial fluctuation or deviation of magnetic layers from collinear alignment and is far more energy efficient. This device operates at room temperature and can be realized with present-day magnetic nanostructure technology. © 2004 American Institute of Physics.
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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
75.60.Jk Magnetization reversal mechanisms
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Interface mixing and phase transformations in Xe-ion-irradiated Co/Fe bilayers

K. Zhang, R. Gupta, G. A. Müller, P. Schaaf, and K. P. Lieb

Appl. Phys. Lett. 84, 3915 (2004); http://dx.doi.org/10.1063/1.1741028 (3 pages) | Cited 13 times

Online Publication Date: 29 April 2004

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Bilayers of polycrystalline Co(37 nm)/Fe(37 nm) were deposited onto Si wafers via electron-gun evaporation and irradiated at room temperature with 200 keV Xe+ ions to fluences of 5×1014–1×1016/cm2. The magneto-optical Kerr effect, Rutherford backscattering spectroscopy and x-ray diffraction were used to characterize the magnetization and microstructure of the films. Xe fluences of up to 5×1015 ions/cm2 were found to induce a four-fold magnetic anisotropy in the originally isotropic films, as a consequence of the phase transformation of hexagonal Co to face-centered-cubic Co caused by ion irradiation. Xe fluences exceeding 7×1015 ions/cm2 produced a uniaxial magnetic texture, which is explained by strong Co/Fe interface mixing and possibly ion-induced formation of CoFe grains at the interface. © 2004 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
78.20.Ls Magneto-optical effects
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

Virgin magnetization of a magnetically shielded superconductor wire: Theory and experiment

Yu. A. Genenko, S. V. Yampolskii, and A. V. Pan

Appl. Phys. Lett. 84, 3921 (2004); http://dx.doi.org/10.1063/1.1741036 (3 pages) | Cited 8 times

Online Publication Date: 29 April 2004

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On the basis of exact solutions to the London equation, the magnetic moment of a type II superconductor filament surrounded by a soft-magnet environment is calculated and the procedure of extracting the superconductor contribution from magnetic measurements is suggested. A comparison of theoretical results with experiments on MgB2/Fe wires allows the estimation of the value of critical current for the first magnetic flux penetration. © 2004 American Institute of Physics.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Sv Critical currents
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Antiferromagnetism at the YBa2Cu3O7/La2/3Ca1/3MnO3 interface

N. Haberkorn, J. Guimpel, M. Sirena, L. B. Steren, W. Saldarriaga, E. Baca, and M. E. Gómez

Appl. Phys. Lett. 84, 3927 (2004); http://dx.doi.org/10.1063/1.1741038 (3 pages) | Cited 17 times

Online Publication Date: 29 April 2004

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The magnetic properties of a series of YBa2Cu3O7−x/La2/3Ca1/3MnO3 (YBCO/LC1/3MO) superlattices grown by dc sputtering at high oxygen pressures (3.5 mbar) show the expected ferromagnetic behavior. However, field-cooled hysteresis loops at a low temperatures show the unexpected existence of exchange bias effect associated with the existence of ferromagnetic/antiferromagnetic (AF) interfaces. The blocking temperature (TB) is found to be thickness dependent and the exchange bias field (HEB) is found to be inversely proportional to the ferromagnetic layer thickness, as expected. The presence of an AF material is probably associated with interface disorder and Mn valence shift toward Mn4+. © 2004 American Institute of Physics.
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75.50.Ee Antiferromagnetics
75.50.Dd Nonmetallic ferromagnetic materials
74.72.-h Cuprate superconductors
74.78.Fk Multilayers, superlattices, heterostructures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
74.25.Ha Magnetic properties including vortex structures and related phenomena
75.30.Et Exchange and superexchange interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Field-effect tuning of carrier density in Nd1.2Ba1.8Cu3Oy thin films

A. Cassinese, G. M. De Luca, A. Prigiobbo, M. Salluzzo, and R. Vaglio

Appl. Phys. Lett. 84, 3933 (2004); http://dx.doi.org/10.1063/1.1745103 (3 pages) | Cited 21 times

Online Publication Date: 29 April 2004

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Using a field effect device we modified the number of holes in the surface layers of 4 to 10 unit cell Nd1.2Ba1.8Cu3Oy (NBCO) epitaxial films grown on (100) SrTiO3 substrates. The results obtained on a set of 12 devices demonstrate that it is possible to induce reversible changes of the hole density of NBCO films by field effect. It is found that the field effect becomes less pronounced increasing the film thickness. Insulating–superconducting transition was observed in one 8 unit cell NBCO field effect device. © 2004 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.62.Yb Other effects
85.25.-j Superconducting devices
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