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20 Oct 2008

Volume 93, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 161101 (2008); http://dx.doi.org/10.1063/1.3000630 (3 pages)

E. Mujagić, L. K. Hoffmann, S. Schartner, M. Nobile, W. Schrenk, M. P. Semtsiv, M. Wienold, W. T. Masselink, and G. Strasser
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Spin transfer torque switching of cobalt nanoparticles

X. J. Wang, H. Zou, and Y. Ji

Appl. Phys. Lett. 93, 162501 (2008); http://dx.doi.org/10.1063/1.3005426 (3 pages) | Cited 4 times

Online Publication Date: 20 October 2008

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Magnetization reversals of cobalt nanoparticles induced by spin transfer torque are demonstrated at 4.2 K by a mechanical point-contact made on a Co/Cu/Co trilayer thin film. The top Co layer ( ∼ 0.5 nm) is discontinuous and consists of isolated cobalt nanoparticles with a diameter of <5 nm. The number of nanoparticles underneath a point contact can be controlled by varying the size of the contact. The characteristics of spin transfer switching are qualitatively different for contacts involving a few particles (5–10) and those involving many particles (40–50).
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Jk Magnetization reversal mechanisms
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys

Topological defects in antiferromagnetically coupled multilayers with perpendicular anisotropy

N. S. Kiselev, U. K. Rößler, A. N. Bogdanov, and O. Hellwig

Appl. Phys. Lett. 93, 162502 (2008); http://dx.doi.org/10.1063/1.2993328 (3 pages) | Cited 7 times

Online Publication Date: 21 October 2008

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A rich variety of specific multidomain textures recently observed in antiferromagnetically coupled multilayers with perpendicular anisotropy include regular (equilibrium) multidomain states as well as different types of topological magnetic defects. Within a phenomenological theory we have classified and analyzed the possible magnetic defects in the antiferromagnetic ground state and determine their structures. The calculated magnetic phase diagrams show the existent regions for all types of magnetic defects. Experimental investigations of the remanent states (observed after different magnetic prehistory) in [Co/Pt]/Ru multilayers with wedged Co layers reveal a corresponding succession of different magnetic defect domain types.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics

Layered antiferromagnetism with high Neel temperature in the intermetallic compound Mn2Au

Sergii Khmelevskyi and Peter Mohn

Appl. Phys. Lett. 93, 162503 (2008); http://dx.doi.org/10.1063/1.3003878 (3 pages) | Cited 3 times

Online Publication Date: 21 October 2008

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On the basis of earlier experimental studies the intermetallic compound Mn2Au has been characterized as a nonmagnetically ordered material. Here we report the results of first-principles calculations based on local spin-density approximation that describes Mn2Au to have a narrow band ground state with rigid local moments on the Mn sites. Calculations of the interatomic exchange constants based on the magnetic force theorem and a Monte Carlo modeling of the resulting Heisenberg-like Hamiltonian predict a high Neel temperature of ∼ 1600 K. This temperature is considerably higher than for the other known high-temperature antiferromagnetic L10-type Mn based binary alloys used in magnetic storage applications.
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75.30.Et Exchange and superexchange interactions
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Ee Antiferromagnetics
71.20.Be Transition metals and alloys
71.28.+d Narrow-band systems; intermediate-valence solids
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Heteroepitaxial growth and optoelectronic properties of layered iron oxyarsenide, LaFeAsO

Hidenori Hiramatsu, Takayoshi Katase, Toshio Kamiya, Masahiro Hirano, and Hideo Hosono

Appl. Phys. Lett. 93, 162504 (2008); http://dx.doi.org/10.1063/1.2996591 (3 pages) | Cited 41 times

Online Publication Date: 22 October 2008

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The epitaxial thin films of LaFeAsO were fabricated on MgO(001) and mixed-perovskite (La,Sr)(Al,Ta)O3(001) single-crystal substrates by pulsed laser deposition using a Nd-doped yttrium aluminum garnet second harmonic source and a 10 at. % F-doped LaFeAsO disk target. Temperature dependences of the electrical resistivities showed no superconducting transition in the temperature range of 2–300 K and were similar to those of undoped polycrystalline bulk samples. The transmittance spectrum exhibited a clear peak at ∼ 0.2 eV, which is explained by ab initio calculations.
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74.78.Fk Multilayers, superlattices, heterostructures
78.30.-j Infrared and Raman spectra
74.25.F- Transport properties
74.25.Gz Optical properties
81.15.Fg Pulsed laser ablation deposition
61.72.up Other materials

Experimental study of domain wall motion in long nanostrips under the influence of a transverse field

S. Glathe, I. Berkov, T. Mikolajick, and R. Mattheis

Appl. Phys. Lett. 93, 162505 (2008); http://dx.doi.org/10.1063/1.2993329 (3 pages) | Cited 26 times

Online Publication Date: 23 October 2008

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We report the real time study of field driven domain wall (DW) motion in giant magnetoresistance nanostrips under the influence of both longitudinal and transverse fields. We have found clear evidence that transverse fields influence the DW dynamics below and above the Walker field [ N. L. Schryer and L. R. Walker, J. Appl. Phys. 45, 5406 (1974) ] drastically. We show the suppression of the Walker breakdown process and a huge enhancement in DW velocity below the Walker field. The maximum velocity reported here is 4500 m/s.
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75.60.Ch Domain walls and domain structure
75.50.Tt Fine-particle systems; nanocrystalline materials
75.47.De Giant magnetoresistance

Magnetic structure near the Co/NiO(001) interface

Elke Arenholz, Gerrit van der Laan, and Frithjof Nolting

Appl. Phys. Lett. 93, 162506 (2008); http://dx.doi.org/10.1063/1.3005643 (3 pages) | Cited 7 times

Online Publication Date: 23 October 2008

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We investigate the magnetic coupling at the Co/NiO interface using soft x-ray magnetic linear dichroism (XMLD) and circular dichroism taking explicitly into account the recently observed angular dependence of the XMLD with respect to the crystallographic axes. We find that the Co moments are aligned perpendicular to the NiO moments. We discuss the impact of the anisotropic XMLD on the intensity ratio of the two peaks at the Ni L2 edge, which is commonly employed to determine the spin orientation in antiferromagnets using XMLD.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities

Oxygen vacancy induced re-entrant spin glass behavior in multiferroic ErMnO3 thin films

S. Y. Jang, D. Lee, J.-H. Lee, T. W. Noh, Y. Jo, M.-H. Jung, and J.-S. Chung

Appl. Phys. Lett. 93, 162507 (2008); http://dx.doi.org/10.1063/1.3006325 (3 pages) | Cited 7 times

Online Publication Date: 23 October 2008

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Epitaxial thin films of hexagonal ErMnO3 fabricated on Pt(111)/Al2O3(0001) and yttria-stabilized zirconia(111) substrates exhibited both ferroelectric character and magnetic ordering at low temperatures. As the temperature was reduced, the ErMnO3 films first showed antiferromagnetism. At lower temperatures, the films deposited at lower oxygen partial pressures exhibited spin glass behavior. This re-entrant spin glass behavior was attributed to competition between an antiferromagnetic interaction in the hexagonal geometry and a ferromagnetic interaction caused by a change in Mn valence induced by excess electrons from the oxygen vacancies.
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75.50.Lk Spin glasses and other random magnets
75.50.Ee Antiferromagnetics
75.80.+q Magnetomechanical effects, magnetostriction
77.80.-e Ferroelectricity and antiferroelectricity
61.72.jd Vacancies
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Geometric dephasing-limited Hanle effect in long-distance lateral silicon spin transport devices

Biqin Huang, Hyuk-Jae Jang, and Ian Appelbaum

Appl. Phys. Lett. 93, 162508 (2008); http://dx.doi.org/10.1063/1.3006333 (3 pages) | Cited 21 times

Online Publication Date: 23 October 2008

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Evidence of spin precession and dephasing (“Hanle effect”) induced by a magnetic field is the only unequivocal proof of spin-polarized conduction electron transport in semiconductor devices. However, when spin dephasing is very strong, Hanle effect in a uniaxial magnetic field can be impossible to measure. Using a silicon device with lateral injector-detector separation of over 2 mm and geometrically induced dephasing making spin transport completely incoherent, we show experimentally and theoretically that Hanle effect can still be measured using a two-axis magnetic field.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Photoinduced magnetic softening of perpendicularly magnetized L10-FePt granular films

Z. Xu, X. D. Liu, R. X. Gao, Z. F. Chen, T. S. Lai, H. N. Hu, S. M. Zhou, X. J. Bai, and J. Du

Appl. Phys. Lett. 93, 162509 (2008); http://dx.doi.org/10.1063/1.3007977 (3 pages) | Cited 3 times

Online Publication Date: 23 October 2008

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Ultrafast spin dynamics has for the first time been studied in perpendicular magnetized granular films. For FePt continuous films and FePt–MgO and FePt–Ag granular films with femtosecond laser excitations, the coercivity HC and the saturation Kerr rotation θKS are dramatically reduced, accompanied by a sharp increase in the reflectivity R. Afterward, these physical quantities are slowly recovered. The changes in HC, θKS, and R are all different among FePt, FePt–MgO, and FePt–Ag films. The difference is caused by different film thicknesses and in particular by the surface plasmon resonance of metallic nanoparticles.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms
78.20.Ls Magneto-optical effects
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

All oxide ferromagnet/semiconductor epitaxial heterostructures

A. Nielsen, A. Brandlmaier, M. Althammer, W. Kaiser, M. Opel, J. Simon, W. Mader, S. T. B. Goennenwein, and R. Gross

Appl. Phys. Lett. 93, 162510 (2008); http://dx.doi.org/10.1063/1.2998576 (3 pages) | Cited 10 times

Online Publication Date: 24 October 2008

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Oxide based ferromagnet/semiconductor heterostructures offer substantial advantages for spin electronics. We have grown (111) oriented Fe3O4 thin films and Fe3O4/ZnO heterostructures on ZnO(0001) and Al2O3(0001) substrates by pulsed laser deposition. High quality crystalline films with mosaic spread as small as 0.03°, sharp interfaces, and rms surface roughness of 0.3 nm were achieved. Magnetization measurements show clear ferromagnetic behavior of the magnetite layers with a saturation magnetization of 3.2μB/f.u. at 300 K. Our results demonstrate that the Fe3O4/ZnO system is an intriguing and promising candidate for the realization of multifunctional heterostructures.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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