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1 Mar 2010

Volume 96, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 96, 091102 (2010); http://dx.doi.org/10.1063/1.3332591 (3 pages)

A. Schropp, P. Boye, J. M. Feldkamp, R. Hoppe, J. Patommel, D. Samberg, S. Stephan, K. Giewekemeyer, R. N. Wilke, T. Salditt, J. Gulden, A. P. Mancuso, I. A. Vartanyants, E. Weckert, S. Schöder, et al.
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Fe diffusion, oxidation, and reduction at the CoFeB/MgO interface studied by soft x-ray absorption spectroscopy and magnetic circular dichroism

A. T. Hindmarch, K. J. Dempsey, D. Ciudad, E. Negusse, D. A. Arena, and C. H. Marrows

Appl. Phys. Lett. 96, 092501 (2010); http://dx.doi.org/10.1063/1.3332576 (3 pages) | Cited 8 times

Online Publication Date: 1 March 2010

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We have studied the effect of annealing on the interface magnetization in a CoFeB/MgO structure which models the lower electrode in a magnetic tunnel junction device. We find that MgO deposition causes Fe to diffuse toward the CoFeB/MgO interface, where it preferentially bonds with oxygen to form a Fe-O-rich interfacial region with reduced magnetization. After annealing at 375 °C the compositional inhomogeneity remains; Fe is reduced back to a ferromagnetic metallic state and the full interfacial magnetization is regained.
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75.60.Nt Magnetic annealing and temperature-hysteresis effects
82.30.-b Specific chemical reactions; reaction mechanisms
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Fourfold symmetric anisotropic magnetoresistance based on magnetocrystalline anisotropy and antiphase boundaries in reactive sputtered epitaxial Fe3O4 films

P. Li, E. Y. Jiang, and H. L. Bai

Appl. Phys. Lett. 96, 092502 (2010); http://dx.doi.org/10.1063/1.3334722 (3 pages) | Cited 8 times

Online Publication Date: 1 March 2010

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The fourfold symmetric anisotropic magnetoresistance (AMR) at high fields in epitaxial Fe3O4 films, which is incompatible with the traditional twofold symmetry, was found to be independent with the current direction but associated with their magnetocrystalline anisotropy. (001)-, (110)-, and (112)-oriented Fe3O4 films show fourfold symmetry in AMR while twofold symmetry appears for (111)-oriented Fe3O4 films. The cubic magnetocrystalline anisotropy field superimposed onto the external magnetic field modifies the alignment of the spins near antiphase boundaries, leading to the oscillating scattering rate for the transport electrons across antiphase boundaries and thus the corresponding fourfold symmetry in AMR.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
72.20.My Galvanomagnetic and other magnetotransport effects
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films

The role of carriers in spin current and magnetic coupling for ZnO:Co diluted magnetic oxides

H. Chou, C. P. Lin, H. S. Hsu, and S. J. Sun

Appl. Phys. Lett. 96, 092503 (2010); http://dx.doi.org/10.1063/1.3309588 (3 pages) | Cited 7 times

Online Publication Date: 1 March 2010

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The role of carriers in the electric conduction and magnetic coupling of diluted magnetic oxides is essential to the spin current formation. This study elucidates the conduction of electrons originating from oxygen vacancies and the magnetic coupling between major doped transition ions. The findings indicate that electrons may conduct in the conduction band or by hopping within discrete localized states. Furthermore, because d-orbital of doped transition ions overlap with these localized states, only hopping electrons contribute to magnetic coupling and spin current formation. Those electrons in the conduction band have no observable effect on magnetic coupling.
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73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
75.50.Pp Magnetic semiconductors
72.20.Ee Mobility edges; hopping transport
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.25.Dk Orbital, charge, and other orders, including coupling of these orders
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Vector magnetic field microscopy using nitrogen vacancy centers in diamond

B. J. Maertz, A. P. Wijnheijmer, G. D. Fuchs, M. E. Nowakowski, and D. D. Awschalom

Appl. Phys. Lett. 96, 092504 (2010); http://dx.doi.org/10.1063/1.3337096 (3 pages) | Cited 11 times

Online Publication Date: 1 March 2010

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The localized spin triplet ground state of a nitrogen vacancy (NV) center in diamond can be used in atomic-scale detection of local magnetic fields. Here we present a technique using ensembles of these defects in diamond to image fields around magnetic structures. We extract the local magnetic field vector by probing resonant transitions of the four fixed tetrahedral NV orientations. In combination with confocal microscopy techniques, we construct a two-dimensional image of the local magnetic field vectors. Measurements are done in external fields less than 50 G and under ambient conditions.
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75.30.Hx Magnetic impurity interactions
71.35.-y Excitons and related phenomena
61.72.jd Vacancies

Interplay between crystallographic orientation and electric transport properties in La2/3Sr1/3MnO3 films

A. Tebano, A. Orsini, D. Di Castro, P. G. Medaglia, and G. Balestrino

Appl. Phys. Lett. 96, 092505 (2010); http://dx.doi.org/10.1063/1.3339872 (3 pages) | Cited 9 times

Online Publication Date: 1 March 2010

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The effect of crystallographic interface orientation on the electric transport properties of fully strained La2/3Sr1/3MnO3 films grown onto LaAlO3 substrates has been investigated. It is found that, relative to the (001) orientation, the (110) orientation strongly enhances the transport properties for film thickness in the range between 3 and 12 nm. Such an effect was ascribed to reduced [relative to the (001) substrates] tetragonal distortion induced by epitaxy onto (110)-oriented substrates. The reduced tetragonal distortion quenches the occupational imbalance between the Mn eg orbitals thus, ultimately, reinforcing the ferromagnetic double exchange transport mechanism.
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73.61.Ng Insulators
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
68.55.J- Morphology of films

Effect of antiferromagnetic order on the dielectric properties of Bi2Fe4O9

Y. A. Park, K. M. Song, K. D. Lee, C. J. Won, and N. Hur

Appl. Phys. Lett. 96, 092506 (2010); http://dx.doi.org/10.1063/1.3339880 (3 pages) | Cited 2 times

Online Publication Date: 1 March 2010

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We investigated the dielectric and magnetic properties of Bi2Fe4O9 single crystals. The dielectric anomalies observed at the magnetic transition temperature indicate that there is a strong coupling between the magnetic and dielectric properties. The anisotropic magnetic contribution of the dielectric constant is discussed in terms of the spin correlation function, 〈Si⋅Sj〉, below the antiferromagnetic transition at 240 K.
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77.22.Ch Permittivity (dielectric function)
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Ultrabroad bandwidth of single-layer electromagnetic attenuation composites with flaky fillers

Z. W. Li, Z. H. Yang, and L. B. Kong

Appl. Phys. Lett. 96, 092507 (2010); http://dx.doi.org/10.1063/1.3340460 (3 pages) | Cited 7 times

Online Publication Date: 2 March 2010

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Z-type barium ferrite flakes were prepared for use as fillers in electromagnetic attenuation composites. The composites with the flaky fillers exhibit greatly enhanced complex permeability, thus achieving an ultrabroad attenuation bandwidth. μ0′ and μmax″ are enhanced by above 150%, and the relative bandwidth WR of 6–7 can be achieved. The bandwidth achieves 75% of the theoretically maximum relative bandwidth. The composites with the flaky fillers are powerful and potential candidates as electromagnetic attenuation materials with ultrabroad bandwidth in L, C, and S bands.
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81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Mesostructural origin of stress-induced magnetic anisotropy in Fe-based nanocrystalline ribbons

Y. Z. Fang, J. J. Zheng, F. M. Wu, Q. M. Xu, J. Q. Zhang, H. Q. Ye, J. L. Zheng, and T. Y. Li

Appl. Phys. Lett. 96, 092508 (2010); http://dx.doi.org/10.1063/1.3330931 (3 pages) | Cited 3 times

Online Publication Date: 2 March 2010

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The cross-sectional mesostructure of a stress-annealed Fe-based (Fe73.5Cu1Nb3Si13.5B9) ribbon (SAR) has been investigated by atomic force microscopy. The magnetic anisotropy field was measured via the curves of the giant magnetoimpedence effect in SAR. The stress-induced magnetic anisotropy field (ΔHk) showed a linear correlation with the transverse congregating vector Kv of the agglomerated grains. This indicated that the ΔHk originated from the directional congregation of the agglomerated grains formed in SAR. A model for this directional congregation has been established. The previous diverse viewpoints on the mechanism of stress-induced magnetic anisotropy have been unified in this model.
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75.30.Gw Magnetic anisotropy
07.79.Lh Atomic force microscopes
75.47.De Giant magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
81.40.Gh Other heat and thermomechanical treatments

Large enhancement of anisotropic magnetoresistance and thermal stability in Ta/NiFe/Ta trilayers with interfacial Pt addition

Y. F. Liu, J. W. Cai, and L. Sun

Appl. Phys. Lett. 96, 092509 (2010); http://dx.doi.org/10.1063/1.3334720 (3 pages) | Cited 5 times

Online Publication Date: 3 March 2010

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Ta/NiFe/Ta trilayers, extensively used for anisotropic magnetoresistance (AMR) sensors, exhibit severely reduced MR ratio at small NiFe thickness and appreciable moment loss, especially after annealing. By inserting ultrathin Pt layers at the interfaces of the trilayers, AMR can be significantly enhanced for thin NiFe films due to the strong electron spin-orbit scattering at Pt/NiFe interfaces along with suppression of interfacial magnetic dead layers. Furthermore, the Pt layers also reduce Ta and NiFe interdiffusion and result in negligible moment loss and AMR degradation after annealing at 350 °C.
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75.47.Np Metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.30.Cr Saturation moments and magnetic susceptibilities
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Rs Electrical and magnetic properties related to treatment conditions

Strain-driven spin reorientation in magnetite/barium titanate heterostructures

G. E. Sterbinsky, B. W. Wessels, J.-W. Kim, E. Karapetrova, P. J. Ryan, and D. J. Keavney

Appl. Phys. Lett. 96, 092510 (2010); http://dx.doi.org/10.1063/1.3330890 (3 pages) | Cited 5 times

Online Publication Date: 3 March 2010

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We report spin reorientation transitions in a Fe3O4/BaTiO3 heterostructure driven by strain at the structural phase transitions of BaTiO3. These spin reorientations result from the emergence of an in-plane uniaxial magnetic anisotropy. The magnetoelastic response of Fe3O4 to the variations in epitaxial strain that occur at the BaTiO3 phase transitions gives rise to the uniaxial anisotropy. The anisotropy energies calculated from the in-plane strain are in quantitative agreement with a change in the Zeeman energy.
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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.)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Gw Magnetic anisotropy
75.80.+q Magnetomechanical effects, magnetostriction
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Co-concentration dependence of half-metallic properties in Co–Mn–Si epitaxial films

Y. Sakuraba, N. Hirose, M. Oogane, T. Nakamura, Y. Ando, and K. Takanashi

Appl. Phys. Lett. 96, 092511 (2010); http://dx.doi.org/10.1063/1.3330942 (3 pages) | Cited 3 times

Online Publication Date: 3 March 2010

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Co-enriched Co2MnSi epitaxial films, i.e., Co2(1+x)Mn1−xSi1−x (CCMS) were fabricated to investigate the Co-concentration dependence of half-metallicity in a Co–Mn–Si Heusler alloy. The tunnel magnetoresistance ratio in the magnetic tunnel junctions with a CCMS electrode slightly reduces with x from −0.02 to 0.13, then suddenly drops at x = 0.20. The half-metallic gap in the G-V curve also disappears when x becomes 0.20. The multiplet structure in x-ray magnetic circular dichroism spectra around Co L-edges, implying half-metallicity of CCMS, also vanishes at x = 0.20. These results consistently indicate the half-metallic nature of CCMS is destroyed when the Co atomic concentration is over 57 at. %.
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78.20.Ls Magneto-optical effects
68.55.-a Thin film structure and morphology
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Suppression of flux avalanches in superconducting films by electromagnetic braking

F. Colauto, E. Choi, J. Y. Lee, S. I. Lee, E. J. Patiño, M. G. Blamire, T. H. Johansen, and W. A. Ortiz

Appl. Phys. Lett. 96, 092512 (2010); http://dx.doi.org/10.1063/1.3350681 (3 pages) | Cited 4 times

Online Publication Date: 4 March 2010

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Magnetic fields perpendicular to superconducting films often trigger vortex avalanches, which always are very harmful for electronic devices and other applications. Such avalanches can be suppressed by a metal layer placed in contact with the superconductor surface, an effect that up to now has been thought to be a consequence of improved heat conduction. Here we show experimentally that the role of the metal layer is not that of a heat-sink, but rather that of an electromagnetic drag due to eddy currents induced in the metal layer during the abrupt onset of the flux avalanches. The effect is demonstrated for films of MgB2 and Nb.
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74.25.Wx Vortex pinning (includes mechanisms and flux creep)
74.78.-w Superconducting films and low-dimensional structures
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Ha Magnetic properties including vortex structures and related phenomena

Giant conductance anisotropy in magnetically coupled Ferromagnet-Superconductor-Ferromagnet structures

A. Belkin, V. Novosad, M. Iavarone, R. Divan, J. Hiller, T. Proslier, J. E. Pearson, and G. Karapetrov

Appl. Phys. Lett. 96, 092513 (2010); http://dx.doi.org/10.1063/1.3352079 (3 pages) | Cited 2 times

Online Publication Date: 5 March 2010

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We demonstrate the evolution of the anisotropic conductivity in the superconductor that is magnetically coupled with two adjacent ferromagnetic layers. Stripe magnetic domain structure in the ferromagnetic layers results in directional superconducting order parameter in the superconducting layer. The conductance anisotropy strongly depends on the period of the magnetic domains and the strength of the local magnetization. The anisotropic conductivity of up to three orders of magnitude can be achieved with spatial critical temperature modulation of 5% of Tc. The effect could be exploited in low temperature nonvolatile logic and storage elements.
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74.78.Fk Multilayers, superlattices, heterostructures
74.62.Yb Other effects
74.25.F- Transport properties
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure

Origin of anomalous hysteresis loops induced by femtosecond laser pulses in GdFeCo amorphous films

Chudong Xu, Zhifeng Chen, Daxin Chen, Shiming Zhou, and Tianshu Lai

Appl. Phys. Lett. 96, 092514 (2010); http://dx.doi.org/10.1063/1.3339878 (3 pages) | Cited 4 times

Online Publication Date: 5 March 2010

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A controllable pump-pulse-number magneto-optical Kerr technique combined with an initializing field scanning approach is developed to eliminate and identify memory and accumulation effects, respectively, from external field history and multiple pulse excitations. A series of anomalous loops of GdFeCo films are measured for different amount of pump pulses using this technique, revealing that serious memory and accumulation effects exist in continuous-pulse-pumped anomalous hysteresis loops which show illusory information of hot coercivity and degree of magnetization reversal. Single-pulse-induced anomalous loop reveals that the hot coercivity shown by continuous-pulse-pumped anomalous loops is not the minimum external field that drives real magneto-optical recording.
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78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials
75.60.Jk Magnetization reversal mechanisms
75.50.Gg Ferrimagnetics
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