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1 Nov 2004

Volume 85, Issue 18, pp. 3959-4247

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 4142 (2004); http://dx.doi.org/10.1063/1.1811774 (3 pages)

Hong Jin Fan, Roland Scholz, Florian M. Kolb, and Margit Zacharias
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Hysteretic current–voltage characteristics and resistance switching at a rectifying Ti∕Pr0.7Ca0.3MnO3 interface

A. Sawa, T. Fujii, M. Kawasaki, and Y. Tokura

Appl. Phys. Lett. 85, 4073 (2004); http://dx.doi.org/10.1063/1.1812580 (3 pages) | Cited 299 times

Online Publication Date: 3 November 2004

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We have characterized the vertical transport properties of epitaxial layered structures composed of Pr0.7Ca0.3MnO3(PCMO) sandwiched between SrRuO3(SRO) bottom electrode and several kinds of top electrodes such as SRO, Pt, Au, Ag, and Ti. Among the layered structures, Ti∕PCMO∕SRO is distinct due to a rectifying I–V characteristic with a large hysteresis. Corresponding to the hysteresis of the I–V characteristics, the contact resistance of the Ti∕PCMO interface reversibly switches between two stable states by applying pulsed voltage stress. We propose a model for the resistance switching at the Ti∕PCMO interface, in which the width and/or height of a Schottky-like barrier are altered by trapped charge carriers in the interface states.
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73.40.Ns Metal-nonmetal contacts
73.61.Le Other inorganic semiconductors
73.40.Cg Contact resistance, contact potential
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.05.Hd Other semiconductors

Observation of ferromagnetism above 900 K in Cr–GaN and Cr–AlN

H. X. Liu, Stephen Y. Wu, R. K. Singh, Lin Gu, David J. Smith, N. Newman, N. R. Dilley, L. Montes, and M. B. Simmonds

Appl. Phys. Lett. 85, 4076 (2004); http://dx.doi.org/10.1063/1.1812581 (3 pages) | Cited 97 times

Online Publication Date: 3 November 2004

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We report ferromagnetism at over 900 K in Cr–GaN and Cr–AlN thin films. The magnetic properties vary as a function of Cr concentration with 60%, and 20%, of the Cr being magnetically active at 3% doping in GaN, and 7% in AlN, respectively. In the GaN sample with the highest magnetically active Cr (60%), channeling Rutherford backscattering indicates that over 70% of Cr impurities are located on substitutional sites. These results give indisputable evidence that substitutional Cr defects are involved in the magnetic behavior. While Cr–AlN is highly resistive, Cr–GaN exhibits properties characteristic of hopping conduction including T−1∕2 resistivity dependence and small Hall mobility (0.06 cm2∕V s). A large negative magnetoresistance is attributed to the influence of the magnetic field on the quantum interference between the many paths linking two hopping sites. The results strongly suggest that ferromagnetism in Cr–GaN and Cr–AlN can be attributed to the double exchange mechanism as a result of hopping between near-midgap substitutional Cr impurity bands.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
73.61.Ey III-V semiconductors
75.30.Cr Saturation moments and magnetic susceptibilities
61.72.S- Impurities in crystals
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.Pq Other materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Control of the magnetic anisotropy of epitaxially grown MnAs∕GaAs ferromagnet-semiconductor hybrid superlattices

J. H. Song, J. J. Lee, Y. Cui, J. B. Ketterson, and Sunglae Cho

Appl. Phys. Lett. 85, 4079 (2004); http://dx.doi.org/10.1063/1.1813630 (3 pages) | Cited 4 times

Online Publication Date: 3 November 2004

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Epitaxial hybrid structures of the ferromagnet–semiconductor superlattice MnAs∕GaAs were grown on GaAs(001) substrates by molecular-beam epitaxy and the dependence of the magnetic properties on the growth temperature and the periodicity were characterized. The magnetic anisotropy is strongly dependent on the surface reconstruction of GaAs(001) substrates. The increase of the periodicity from 5 nm∕5 nm to 10 nm∕10 nm also changes the magnetic anisotropy. These results demonstrate that the surface reconstruction of the substrate and the periodicity determine the magnetic structure of the MnAs∕GaAs superlattices.
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68.65.Cd Superlattices
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
75.30.Gw Magnetic anisotropy
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Atomic-scale structural analyses of epitaxial Co∕Re superlattices

Wentao Xu, Lance E. De Long, Timothy Charlton, Matthew Chisholm, and David Lederman

Appl. Phys. Lett. 85, 4082 (2004); http://dx.doi.org/10.1063/1.1813626 (3 pages) | Cited 1 time

Online Publication Date: 3 November 2004

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High-resolution transmission electron microscopy and scanning transmission electron microscopy (STEM) have been used to investigate atomic-scale structural properties of Co∕Re trilayers and superlattices grown via magnetron sputtering. The sample growth was epitaxial with the (10math0) plane of Co and Re parallel to the (11math0) plane of Al2O3, and the [001] direction of Re and Co coinciding with that of the Al2O3. Both low-angle and high-angle Z-contrast STEM images show a very uniform layer thickness. However, the interface roughness between the Re and Co layers monotonically increases with interface distance from the substrate. These results strongly imply that, in the epitaxial Re∕Co superlattice system, interface roughness plays a more important role in the giant magnetoresistance effect than thickness fluctuations of the spacer layer. Previous anisotropic magnetoresistance measurements can be explained in terms of the observed atomic-scale structure.
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68.65.Cd Superlattices
68.65.Ac Multilayers
75.47.De Giant magnetoresistance
72.15.Gd Galvanomagnetic and other magnetotransport effects
68.35.Ct Interface structure and roughness
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
81.15.Cd Deposition by sputtering
68.37.Lp Transmission electron microscopy (TEM)

Domain-size-dependent exchange bias in Co∕LaFeO3

A. Scholl, F. Nolting, J. W. Seo, H. Ohldag, J. Stöhr, S. Raoux, J.-P. Locquet, and J. Fompeyrine

Appl. Phys. Lett. 85, 4085 (2004); http://dx.doi.org/10.1063/1.1813633 (3 pages) | Cited 16 times

Online Publication Date: 3 November 2004

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X-ray microscopy using magnetic linear dichroism of a zero-field-grown multidomain Co∕LaFeO3 ferromagnet∕antiferromagnet sample shows a local exchange bias of random direction and magnitude. A statistical analysis of the local bias of individual micron-size magnetic domains demonstrates an increasing bias field with decreasing domain size as expected for a random distribution of pinned, uncompensated spins, which are believed to mediate the interface coupling. A linear dependence with the inverse domain diameter is found.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
68.37.Yz X-ray microscopy
75.30.Et Exchange and superexchange interactions

Flux pinning behavior of incomplete multilayered lattice structures in YBa2Cu3O7−d

Paul N. Barnes, Timothy J. Haugan, Chakrapani V. Varanasi, and Timothy A. Campbell

Appl. Phys. Lett. 85, 4088 (2004); http://dx.doi.org/10.1063/1.1809274 (3 pages) | Cited 31 times

Online Publication Date: 3 November 2004

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Magnetization results of YBa2Cu3O7−d films processed with interlayers of CeO2 inclusions are presented. Unexpected flux pinning results that are different from previous observations with nanoparticulate layered inclusions were observed. Flux pinning was found to be in some cases either slightly improved at either low fields <0.5 T or in other cases at high fields >8 T although degraded, sometimes severely, at interim magnetic fields. Most unexpectedly, the pinning performance of the various samples rapidly converges as the temperature is reduced from 77 to 65 K, causing all films to have similar Jc(H) behavior at 65 K even though dramatically different at 77 K.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Ha Magnetic properties including vortex structures and related phenomena
61.72.Qq Microscopic defects (voids, inclusions, etc.)
74.25.Sv Critical currents

Bistable superconducting quantum interference device with built-in switchable π∕2 phase shift

Henk-Jan H. Smilde, Ariando, Horst Rogalla, and Hans Hilgenkamp

Appl. Phys. Lett. 85, 4091 (2004); http://dx.doi.org/10.1063/1.1812813 (3 pages) | Cited 8 times

Online Publication Date: 3 November 2004

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Superconducting quantum interference devices (SQUIDs) have been realized with a built-in π∕2 phase shift of the superconducting wave function. Its design is inspired by the phase-shifter concept, first proposed by Ioffe et al. [Nature 398, 679 (1999)] as the key element in a solid-state qubit configuration. It exploits the dx2−y2 order parameter symmetry in the high-Tc cuprates in multilayer structures based on YBa2Cu3O7-Nb ramp-type Josephson contacts. By reversing the sign of the persistent circulating current in the phase-shifting element, the π∕2 SQUID can be controllably switched between two energetically degenerate ground states, with complementary magnetic flux dependencies.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
73.23.Ra Persistent currents
74.25.Sv Critical currents

Precession-dominated switching of synthetic antiferromagnets

Joo-Von Kim, T. Devolder, C. Chappert, C. Maufront, and R. Fournel

Appl. Phys. Lett. 85, 4094 (2004); http://dx.doi.org/10.1063/1.1812576 (3 pages) | Cited 5 times

Online Publication Date: 3 November 2004

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We present theoretical results of precession-dominated switching of synthetic antiferromagnet elements. A fast (subnanosecond) reversal mode is shown to be possible for perfectly compensated structures (zero net moment) with pulsed magnetic fields, where the antiparallel alignment is largely preserved during reversal. By using component ferromagnets with different magnetocrystalline and shape anisotropies, we show that it is possible to select the final magnetic state of the synthetic antiferromagnet with pulsed fields alone. Applications to magnetic memory devices are discussed.
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75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy

Enhancement of rare-earth–transition-metal exchange interaction in Pr2Fe17 probed by inelastic neutron scattering

N. Magnani, S. Carretta, G. Amoretti, L. Pareti, A. Paoluzi, R. Caciuffo, and J. A. Stride

Appl. Phys. Lett. 85, 4097 (2004); http://dx.doi.org/10.1063/1.1814819 (3 pages) | Cited 2 times

Online Publication Date: 3 November 2004

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The fundamental magnetic interactions of Pr2Fe17 are studied by inelastic neutron scattering and anisotropy field measurements. Data analysis confirms the presence of three magnetically inequivalent sites, and reveals an exceptionally large value of the exchange field. The unexpected importance of J-mixing effects in the description of the ground-state properties of Pr2Fe17 is shown, and possible applications of related compounds are envisaged.
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75.50.Bb Fe and its alloys
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy

Magnetic anisotropy of Fe3Pt alloy thin films

M. A. I. Nahid and Takao Suzuki

Appl. Phys. Lett. 85, 4100 (2004); http://dx.doi.org/10.1063/1.1815070 (3 pages) | Cited 6 times

Online Publication Date: 3 November 2004

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The magnetic anisotropy constants of Fe3Pt alloy thin films grown onto MgO(100) and MgO(111) substrates by electron-beam evaporation are investigated in conjunction with structure. It is observed that the orientation of the Fe3Pt films depends on the substrate. Both oriented samples exhibit very large in-plane magnetic anisotropy. The magnetic anisotropy constants K1 and K2 are found to strongly depend on the deposition temperature (TS). The maximum values of K1 and K2 obtained are about −4×106 and 2×107 erg∕cc, respectively. A close relationship is observed between the magnetic anisotropy constants and structural parameter.
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75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth

Magnetic and morphological characteristics of nickel nanoparticles films produced by femtosecond laser ablation

G. Ausanio, A. C. Barone, V. Iannotti, L. Lanotte, S. Amoruso, R. Bruzzese, and M. Vitiello

Appl. Phys. Lett. 85, 4103 (2004); http://dx.doi.org/10.1063/1.1815065 (3 pages) | Cited 24 times

Online Publication Date: 3 November 2004

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We have used the technique of femtosecond (fs) laser ablation in a vacuum to produce films of nickel nanoparticles. A peculiarity of this fs laser deposition is the significant shape and orientation anisotropy of the nanoparticles, which are oblate ellipsoids with the major axis parallel to the deposition substrate. The deposited films present unique magnetic properties, and, in specific conditions, very high remanence ratios (up to 0.7) accompanied with relatively low values of saturation and coercive fields can be obtained. We have interpreted these results in terms of the mentioned anisotropies, and of the occurrence of a thermally induced in-plane tensile stress, which is a function of the nanoparticles size.
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81.07.Wx Nanopowders
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
78.47.-p Spectroscopy of solid state dynamics
68.60.Bs Mechanical and acoustical properties
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