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24 Sep 2007

Volume 91, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 91, 132501 (2007); http://dx.doi.org/10.1063/1.2786856 (3 pages)

V. Rose, X. M. Cheng, D. J. Keavney, J. W. Freeland, K. S. Buchanan, B. Ilic, and V. Metlushko
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The breakdown of the fingerprinting of vortices by hysteresis loops in circular multilayer ring arrays

V. Rose, X. M. Cheng, D. J. Keavney, J. W. Freeland, K. S. Buchanan, B. Ilic, and V. Metlushko

Appl. Phys. Lett. 91, 132501 (2007); http://dx.doi.org/10.1063/1.2786856 (3 pages) | Cited 7 times

Online Publication Date: 24 September 2007

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Microscale single-layer ferromagnetic rings typically exhibit a magnetic vortex state at remanence, characterized by a flux-closed magnetic state with zero stray fields. Magnetic reversal in such systems yields a vanishing remanent magnetization. In contrast, the authors show that in individual layers in thin rings, which alternate magnetic and nonmagnetic materials (NiFe/Cu/Co), layer-resolved hysteresis loops, measured using x-ray resonant magnetic scattering, exhibit the characteristics of a vortex formation, although photoelectron emission microscopy and micromagnetic simulations clearly prove that multidomain states are formed. This result is of considerable importance for the development of pseudo-spin-valve-type structures for applications.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure

Current-induced domain wall depinning and magnetoresistance in La0.7Sr0.3MnO3 planar spin valves

A. Ruotolo, A. Oropallo, F. Miletto Granozio, G. P. Pepe, P. Perna, U. Scotti di Uccio, and D. Pullini

Appl. Phys. Lett. 91, 132502 (2007); http://dx.doi.org/10.1063/1.2784940 (3 pages) | Cited 13 times

Online Publication Date: 24 September 2007

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The authors have performed experiments on current-induced domain wall (DW) displacement in La0.7Sr0.3MnO3 nanostructures patterned by gallium (Ga) focused-ion-beam milling. A dc current is found to assist or hinder, according to polarity, an external magnetic field in the depinning of a DW trapped in a nanoconstriction. For large enough currents, the DW depinning occurs in the absence of external magnetic field. The depinning current depends on the transverse anisotropy constant of the region toward which the DW is displaced.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ch Domain walls and domain structure
75.47.Pq Other materials
75.30.Gw Magnetic anisotropy
72.20.My Galvanomagnetic and other magnetotransport effects

Role of long range ferromagnetic order in the electronic structure of Sr1−xCaxRuO3

Ravi Shankar Singh, V. R. R. Medicherla, and Kalobaran Maiti

Appl. Phys. Lett. 91, 132503 (2007); http://dx.doi.org/10.1063/1.2789731 (3 pages) | Cited 4 times

Online Publication Date: 24 September 2007

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We investigate the role of long range ferromagnetic order in the electronic structure of Sr1−xCaxRuO3 using high resolution photoemission spectroscopy. SrRuO3 is a ferromagnetic metal but isostructural, isoelectronic CaRuO3 is an enhanced paramagnet. Surface spectra of CaRuO3 exhibit temperature induced modifications. This is not significant in other compositions. This may be attributed to the structural changes observed in previous studies. Interestingly, the bulk spectra reveal unusual spectral changes exhibiting a large decrease in the coherent feature intensity corresponding to only ferromagnetic samples, although the Ru moment is very similar in all compositions.
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75.50.Dd Nonmetallic ferromagnetic materials
71.20.Ps Other inorganic compounds
75.20.Ck Nonmetals
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

High bias voltage effect on spin-dependent conductivity and shot noise in carbon-doped Fe(001)/MgO(001)/Fe(001) magnetic tunnel junctions

R. Guerrero, D. Herranz, F. G. Aliev, F. Greullet, C. Tiusan, M. Hehn, and F. Montaigne

Appl. Phys. Lett. 91, 132504 (2007); http://dx.doi.org/10.1063/1.2793619 (3 pages) | Cited 21 times

Online Publication Date: 26 September 2007

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Low temperature (10 K) high voltage bias dynamic conductivity (up to 2.7 V) and shot noise (up to 1 V) were studied in epitaxial Fe(100)/Fe–C/MgO(100)/Fe(100) magnetic tunnel junctions as a function of the magnetic state. The junctions show large tunnel magnetoresistance (185% at 300 K and 330% at 4 K). Multiple sign inversion of the magnetoresistance is observed for bias polarity when the electrons scan the electronic structure of the bottom Fe–C interface. The shot noise shows a Poissonian character. This demonstrates a pure spin-dependent direct tunneling mechanism and validates the high structural quality of the MgO barrier.
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75.47.Np Metals and alloys
72.70.+m Noise processes and phenomena

Magnetic multilayers on porous anodized alumina for percolated perpendicular media

M. Tofizur Rahman, Nazmun Nahar Shams, Yun-Chung Wu, Chih-Huang Lai, and Dieter Suess

Appl. Phys. Lett. 91, 132505 (2007); http://dx.doi.org/10.1063/1.2790788 (3 pages) | Cited 22 times

Online Publication Date: 26 September 2007

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Co/Pt multilayers deposited on anodized alumina substrates are introduced as percolated perpendicular media. The pores act as pinning sites due to variations of thickness and anisotropy direction around the perimeters. Coercivity, domain size, and switching field can be engineered by controlling pore density. The media exhibit strong perpendicular anisotropy and the switching field remains unchanged at its minimum up to an angular deviation of 50° from the easy axis. A better tolerance of switching-field distributions can thus be achieved, which may help to achieve a high signal-to-noise ratio. The thermal stability of the proposed media is investigated by micromagnetic simulations.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Cc Other ferromagnetic metals and alloys
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
68.65.Ac Multilayers

Low temperature deposited L10 FePt–C (001) films with high coercivity and small grain size

J. S. Chen, B. C. Lim, J. F. Hu, B. Liu, G. M. Chow, and G. Ju

Appl. Phys. Lett. 91, 132506 (2007); http://dx.doi.org/10.1063/1.2789790 (3 pages) | Cited 34 times

Online Publication Date: 26 September 2007

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FePt–C films with high coercivity, (001) texture, and small grain size were deposited on MgO/CrRu/glass substrate by cosputtering FePt and carbon at 350 °C. The out-of-plane coercivity measured at room temperature increased from 9.6 to 15.1 kOe when C concentrations increased from 0% to 15%. Further increasing the C contents to 20% and 25% caused the decrease of coercivity to 13.6 and 11.8 kOe, respectively. With C doping, a two-layer structure of FePt–C films was formed and fcc-phase FePt particles were found. By optimizing the sputtering process, FePt–C (001) film with coercivity higher than 14.4 kOe and columnar FePt grains of 7.5 nm in diameter was obtained, which are suitable for ultrahigh density perpendicular recording.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Cd Deposition by sputtering
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth

Exchange shift of stripe domains in antiferromagnetically coupled multilayers

N. S. Kiselev, I. E. Dragunov, U. K. Rößler, and A. N. Bogdanov

Appl. Phys. Lett. 91, 132507 (2007); http://dx.doi.org/10.1063/1.2793626 (3 pages) | Cited 10 times

Online Publication Date: 27 September 2007

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Antiferromagnetically coupled multilayers with perpendicular anisotropy, such as [CoPt]/Ru, Co/Ir, and Fe/Au, display ferromagnetic stripe phases as the ground states. It is theoretically shown that the antiferromagnetic interlayer exchange causes a relative shift of domains in adjacent layers. This “exchange shift” is responsible for several recently observed effects: an anomalous broadening of domain walls, the formation of the so-called “tiger-tail” patterns, and a “mixed state” of antiferromagnetic and ferromagnetic domains in [CoPt]/Ru multilayers. The derived analytical relations between the values of the shift and the strength of antiferromagnetic coupling provide an effective method for a quantitative determination of the interlayer exchange interactions.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ee Antiferromagnetics
75.50.Cc Other ferromagnetic metals and alloys
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure

Nanostructure of chemically phase separated La–Ce–Mn–O thin films

C. Stingl, V. Moshnyaga, Y. Luo, B. Damaschke, K. Samwer, and M. Seibt

Appl. Phys. Lett. 91, 132508 (2007); http://dx.doi.org/10.1063/1.2790494 (3 pages) | Cited 2 times

Online Publication Date: 27 September 2007

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The perovskite compound La0.67Ce0.33MnO3 (LCeMO) is a candidate for electron doping rather than the hole doping common in manganites. However, it is not clear whether Ce, which has a smaller ionic radius than other dopants, can be incorporated into the crystal lattice. Thin LCeMO films were prepared by two different deposition techniques. In both cases, a chemical phase separation is observed, which in one case leads to a self-organized columnar nanostructure with no indication for n-type doping. In the other case, we find hole doping induced by La vacancies.
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75.70.Ak Magnetic properties of monolayers and thin films
75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
61.46.Hk Nanocrystals
64.75.-g Phase equilibria
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

The rectification of radio-frequency signal by magnetic domain wall in a single-layered ferromagnetic nanowire

A. Yamaguchi, H. Miyajima, T. Ono, Y. Suzuki, and S. Yuasa

Appl. Phys. Lett. 91, 132509 (2007); http://dx.doi.org/10.1063/1.2793620 (3 pages) | Cited 7 times

Online Publication Date: 28 September 2007

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The rectifying effect of a constant-wave radio frequency (rf) current by a magnetic domain wall (DW) in a single-layered ferromagnetic wire is presented. A direct-current (dc) voltage is generated by the spin torque diode effect, which is a consequence of magnetoresistance oscillation due to the resonant spin wave excitation induced by the spin-polarized rf current. The dc voltage spectrum strongly depends on the internal spin structure in the DW, which corresponds to the magnetic fingerprint of the spin structure in the ferromagnetic wire.
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73.40.Ei Rectification
75.60.Ch Domain walls and domain structure
75.30.Ds Spin waves
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
72.25.Mk Spin transport through interfaces
75.47.Np Metals and alloys

Element specific separation of bulk and interfacial magnetic hysteresis loops

A. K. Suszka, C. J. Kinane, C. H. Marrows, B. J. Hickey, D. A. Arena, J. Dvorak, A. Lamperti, B. K. Tanner, and S. Langridge

Appl. Phys. Lett. 91, 132510 (2007); http://dx.doi.org/10.1063/1.2790492 (3 pages) | Cited 3 times

Online Publication Date: 28 September 2007

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We have studied the reversal of the bulk and interfacial magnetizations of the free layer of a spin valve using soft x-ray resonant magnetic scattering. By dusting the interface of the NiFe free layer with a few angströms of Co, we were able to distinguish between the interfacial and bulk magnetisms by tuning the x-ray photon energy. We measured hysteresis loops of reflected x-ray intensity at selected points in reciprocal space. We find no difference in the switching fields, showing that in transition metal ferromagnets, the exchange interactions are sufficiently strong to prevent a separate interfacial coercivity from arising.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
78.70.Ck X-ray scattering

Gyrotropic linear and nonlinear motions of a magnetic vortex in soft magnetic nanodots

Ki-Suk Lee and Sang-Koog Kim

Appl. Phys. Lett. 91, 132511 (2007); http://dx.doi.org/10.1063/1.2783272 (3 pages)

Online Publication Date: 28 September 2007

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The authors investigated the gyrotropic linear and nonlinear motions of a magnetic vortex in soft magnetic cylindrical nanodots under in-plane oscillating magnetic fields of different frequencies and amplitudes, by employing both micromagnetic simulations and the numerical solutions of Thiele’s equation of motion [ Phys. Rev. Lett. 30, 230 (1973) ]. Not only noncircular elliptical vortex-core orbital trajectories in the linear regime but also complex trajectories including stadiumlike shape in the nonlinear regime were observed from the micromagnetic simulations and were in excellent agreement with the numerical solutions of the analytical equations of motion. It was verified that the numerical solutions of Thiele’s equation are promisingly applicable in order to predict and describe well such complex vortex gyrotropic linear and nonlinear motions in both the initial transient and later steady states. These results enrich the fundamental understanding of the linear and nonlinear motions of vortices in confined magnetic elements in response to oscillating driving forces.
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75.75.-c Magnetic properties of nanostructures
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.40.Mg Numerical simulation studies
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.-m Intrinsic properties of magnetically ordered materials
75.50.Bb Fe and its alloys

Small reversible axial-strain window for the critical current of a high performance Nb3Sn superconducting strand

Xi Feng Lu, Stephen Pragnell, and Damian P. Hampshire

Appl. Phys. Lett. 91, 132512 (2007); http://dx.doi.org/10.1063/1.2789696 (3 pages) | Cited 12 times

Online Publication Date: 28 September 2007

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The engineering critical current density (JC) of a Nb3Sn restacked-rod-process superconducting strand is reported as a function of magnetic field (B ⩽ 28 T), applied axial strain (−0.9% ⩽ εA ⩽ 0.2%), and temperature (4.2 K ⩽ T ⩽ 14 K). Although the strain tolerance of JC is similar to other strands, the strain range over which JC is reversible is limited in both tension and compression. Samples were partially damaged when the intrinsic strain (εI) was increased from −0.74% to −0.97% in compression and grossly damaged when εI was only 0.13% in tension.
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74.25.Sv Critical currents
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Ld Mechanical and acoustical properties, elasticity, and ultrasonic attenuation
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