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6 Jun 2011

Volume 98, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 233101 (2011); http://dx.doi.org/10.1063/1.3597211 (3 pages)

Yu-Jung Lu (呂宥蓉), Hon-Way Lin (林弘偉), Hung-Ying Chen (陳虹穎), Yu-Chen Yang (楊右丞), and Shangjr Gwo (果尚志)
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Epitaxial growth of the high temperature ferromagnetic semiconductor Fe1.5Ti0.5O3 on silicon-compatible substrate

Ali Hamie, Elena Popova, Yves Dumont, Ekaterina Chikoidze, Bénédicte Warot-Fonrose, Bruno Berini, and Niels Keller

Appl. Phys. Lett. 98, 232501 (2011); http://dx.doi.org/10.1063/1.3595271 (3 pages) | Cited 2 times

Online Publication Date: 6 June 2011

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The ilmenite-hematite (IH) solid solution Fe1.5Ti0.5O3 thin films with rhombohedral symmetry were epitaxially grown on silicon-compatible cubic SrTiO3(001) substrates. Ordered (R-3 symmetry) and disordered (R-3c symmetry) cation arrangement along the film c axis was obtained for different oxygen pressure during the IH growth. Drastic changes in magnetic properties of the films were observed as a function of the cation order. The IH thin films with R-3 symmetry have relatively high conductivity and saturation magnetization at 300 K (6 Ω−1 cm−1 and 0.4 μB/Fe respectively), and Curie temperature of 415 K, making IH a promising material for room-temperature spintronics applications.
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68.55.ag Semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Anisotropy induced large exchange bias behavior in ball milled Ni–Co–Mn–Sb alloys

Ajaya K. Nayak, Roshnee Sahoo, K. G. Suresh, A. K. Nigam, X. Chen, and R. V. Ramanujan

Appl. Phys. Lett. 98, 232502 (2011); http://dx.doi.org/10.1063/1.3597305 (3 pages) | Cited 3 times

Online Publication Date: 6 June 2011

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We report the effect of decrease in the grain size on the structural, magnetic and exchange bias (EB) behavior in ball milled Ni50−xCoxMn38Sb12 (x = 0 and 5) Heusler alloys. The existence of a wide range of grain sizes in the ball milled samples results in dramatic changes in the structural and magnetic properties. For x = 0, a large EB field of 3.2 kOe is observed in the ball milled sample, compared to a value of 245 Oe of the bulk sample. This increase is attributed to the enhanced exchange coupling between the soft and hard magnetic particles.
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75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
81.05.Bx Metals, semimetals, and alloys
81.20.Wk Machining, milling

Significant spin polarization of Co2MnGa Heusler thin films on MgO(100) measured by ultraviolet photoemission spectroscopy

Michaela Hahn, Gerd Schönhense, Elena Arbelo Jorge, and Martin Jourdan

Appl. Phys. Lett. 98, 232503 (2011); http://dx.doi.org/10.1063/1.3597315 (3 pages) | Cited 1 time

Online Publication Date: 6 June 2011

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The spin dependent valence band structure of the Heusler compound Co2MnGa grown on MgO(100) is investigated by spin resolved ultraviolet photoemission spectroscopy (SRUPS). Using a vacuum suitcase, epitaxial thin film samples are transferred from a deposition chamber into an SRUPS chamber with a highly efficient spin detector. The transport results only in weak oxidation of the moderately reactive compound Co2MnGa. A spin polarization of 34% is obtained at the Fermi energy. The energy dependence of the spin polarization including a sign change at E−EF = −0.6 eV is in good agreement with theoretical predictions of the bulk properties of the Heusler compound.
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73.20.At Surface states, band structure, electron density of states

Finite tunnel magnetoresistance at the compensation point of Sm1−xGdxAl2, a ferromagnetic electrode with zero magnetization

M. Da Silva, K. Dumesnil, C. Dufour, M. Hehn, D. Pierre, D. Lacour, F. Montaigne, G. Lengaigne, and S. Robert

Appl. Phys. Lett. 98, 232504 (2011); http://dx.doi.org/10.1063/1.3597625 (3 pages)

Online Publication Date: 6 June 2011

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A tunnel magnetoresistance effect is observed in magnetic tunnel junctions with an original zero magnetization ferromagnetic electrode composed of Sm1−xGdxAl2. A finite tunnel magnetoresistance is measured when the Sm1−xGdxAl2 electrode is in a magnetic compensated state proving that Sm1−xGdxAl2 with zero magnetization is able to give rise to a spin-polarized current. The temperature dependence of tunnel magnetoresistance reveals that this effect is related to the relative orientation of spin contributions to magnetic moment in both electrodes and that the tunnel polarization of the Sm1−xGdxAl2 electrode is negative.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.50.Cc Other ferromagnetic metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.76.+j Spin transport effects
75.30.Cr Saturation moments and magnetic susceptibilities

Power generation transducer from magnetostrictive materials

Hui Zhang

Appl. Phys. Lett. 98, 232505 (2011); http://dx.doi.org/10.1063/1.3597222 (3 pages) | Cited 3 times

Online Publication Date: 8 June 2011

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In this letter, on the basis of Stoner-Wohlfarth model, the changes in magnetization of Tb0.3Dy0.7Fe2 alloy have been calculated with a compressive stress along the [111] and [112] axes. The results have shown that the significant change in magnetization for Tb0.3Dy0.7Fe2 alloy can be induced by the compressive stress. A feasible application of power generation floor which can convert the energy from the vibration created by a walking person on it into electric energy has been proposed, and its structure and performance also have been revealed.
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85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
75.80.+q Magnetomechanical effects, magnetostriction
84.60.-h Direct energy conversion and storage

Enhanced magnetoresistance in naturally oxidized MgO-based magnetic tunnel junctions with ferromagnetic CoFe/CoFeB bilayers

D. K. Schreiber, Y-S Choi, Yuzi Liu, Ann N. Chiaramonti, David N. Seidman, and A. K. Petford-Long

Appl. Phys. Lett. 98, 232506 (2011); http://dx.doi.org/10.1063/1.3597224 (3 pages) | Cited 1 time

Online Publication Date: 8 June 2011

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Three-dimensional elemental distributions in magnetic tunnel junctions containing naturally oxidized MgO tunnel barriers are characterized using atom-probe tomography. Replacing the CoFeB free layer (reference layer) with a CoFe/CoFeB (CoFeB/CoFe) bilayer increases the magnetoresistance from 105% to 192% and decreases the resistance-area product from 14.5 to 3.4 Ω μm2. The CoFe/CoFeB bilayer improves the compositional uniformity within the free layer by nucleating CoFeB crystals across the entire layer, resulting in a homogeneous barrier/free layer interface. In contrast, the simple CoFeB free layer partially crystallizes with composition differences from grain to grain (5–30 nm), degrading the tunnel junction performance.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys

Coercivity of ordered arrays of magnetic Co nanowires with controlled variable lengths

L. G. Vivas, R. Yanes, O. Chubykalo-Fesenko, and M. Vazquez

Appl. Phys. Lett. 98, 232507 (2011); http://dx.doi.org/10.1063/1.3597227 (3 pages) | Cited 8 times

Online Publication Date: 8 June 2011

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Ordered hexagonal arrays of Co nanowires were prepared using anodic aluminum oxide templates, varying the nanowire length in a controlled way. The measured coercivity values were shown to decrease with the increase in the nanowire aspect ratio, in contrast to the behavior expected from the shape anisotropy. The measurements were interpreted considering the change in the preferred crystalline structure, from fcc cubic to hcp hexagonal in small and high aspect ratio nanowires, respectively. The experimental evolution of coercivity with nanowires length is interpreted considering micromagnetic simulations taking into account the change in their crystalline structure.
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75.75.Cd Fabrication of magnetic nanostructures
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
81.07.Gf Nanowires

Strongly quadrature-dependent noise in superconducting microresonators measured at the vacuum-noise limit

J. Gao, L. R. Vale, J. A. B. Mates, D. R. Schmidt, G. C. Hilton, K. D. Irwin, F. Mallet, M. A. Castellanos-Beltran, K. W. Lehnert, J. Zmuidzinas, and H. G. Leduc

Appl. Phys. Lett. 98, 232508 (2011); http://dx.doi.org/10.1063/1.3597156 (3 pages) | Cited 5 times

Online Publication Date: 9 June 2011

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We measure frequency- and dissipation-quadrature noise in superconducting microresonators with sensitivity near the vacuum noise level using a Josephson parametric amplifier. At an excitation power of 100 nW, frequency noise rises orders of magnitude above the vacuum noise, but no excess dissipation-quadrature noise is observed above the vacuum noise level. Our results suggest that using quantum amplifiers in dissipation measurement may greatly improve the sensitivity of microresonator readout, which has important implications for applications such as detectors, qubits, and nanomechanical oscillators.
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85.25.Cp Josephson devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
84.30.Le Amplifiers

Magnetocaloric effect in layered NdMn2Ge0.4Si1.6

J. L. Wang, S. J. Campbell, J. M. Cadogan, A. J. Studer, R. Zeng, and S. X. Dou

Appl. Phys. Lett. 98, 232509 (2011); http://dx.doi.org/10.1063/1.3599456 (3 pages) | Cited 8 times

Online Publication Date: 9 June 2011

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A giant magnetocaloric effect has been observed in NdMn2Ge0.4Si1.6 associated with the first-order magnetic phase transition from antiferromagnetism to ferromagnetism around TC = 36 K. The magnetic entropy change –ΔSM and adiabatic temperature change ΔTad have been determined from magnetization and specific heat measurements (B = 0–5 T) with –ΔSM calculated by the Maxwell relation and Clausius–Clapeyron method. The values –ΔSMmax = 12.3 J kg−1 K−1 and refrigerant capacity ∼ 95 J/kg for ΔB = 0–2 T as derived from the Maxwell relation, together with the small hysteresis (thermal <0.5 K; magnetic field <0.1 T), indicate the potential of NdMn2Ge0.4Si1.6 for refrigeration applications.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ee Antiferromagnetics
75.50.Cc Other ferromagnetic metals and alloys

Large change in perpendicular magnetic anisotropy induced by an electric field in FePd ultrathin films

F. Bonell, S. Murakami, Y. Shiota, T. Nozaki, T. Shinjo, and Y. Suzuki

Appl. Phys. Lett. 98, 232510 (2011); http://dx.doi.org/10.1063/1.3599492 (3 pages) | Cited 12 times

Online Publication Date: 9 June 2011

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The magnetic properties of FePd ultrathin films and their variation under the influence of an electric field are investigated by magneto-optical Kerr effect (MOKE) measurements. L10-ordered FePd shows a spin reorientation transition when varying the thickness. The easy axis of magnetization is found to be normal to the plane at thicknesses above 9 monolayers (MLs) and in-plane below 9 ML. The coercive field, the perpendicular magnetic anisotropy and the MOKE signal at saturation vary with the applied electric field. The sensitivity of the interface magnetic anisotropy is estimated to be 602 fJ/V m.
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75.70.Ak Magnetic properties of monolayers and thin films
78.66.Bz Metals and metallic alloys
75.30.Gw Magnetic anisotropy
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Direct observation of antiferromagnetically oriented spin vortex states in magnetic multilayer elements

S. Wintz, T. Strache, M. Körner, M. Fritzsche, D. Markó, I. Mönch, R. Mattheis, J. Raabe, C. Quitmann, J. McCord, A. Erbe, and J. Fassbender

Appl. Phys. Lett. 98, 232511 (2011); http://dx.doi.org/10.1063/1.3597297 (3 pages) | Cited 2 times

Online Publication Date: 9 June 2011

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We report on the coupling of spin vortices in magnetic multilayer elements. The magnetization distribution in thin film disks consisting of two ferromagnetic layers separated by a nonmagnetic spacer is imaged layer-resolved by using x-ray microscopy. We directly observe two fundamentally different vortex coupling states, namely antiferromagnetic and ferromagnetic orientation of the flux directions. It is found that these states are predetermined for systems that involve a sufficiently strong interlayer exchange coupling, whereas for the case of a purely dipolar interaction both states are transformable into each other.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Asymmetric domain wall depinning under current in spin valves with perpendicular anisotropy

S. Park, N. M. Nguyen, C. Burrowes, E. E. Fullerton, C. Chappert, L. Prejebeanu, F. Garcia-Sanchez, and D. Ravelosona

Appl. Phys. Lett. 98, 232512 (2011); http://dx.doi.org/10.1063/1.3592844 (3 pages) | Cited 2 times

Online Publication Date: 10 June 2011

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We have studied the current induced domain wall depinning from an artificial constriction in Co/Ni multilayer spin valves with perpendicular magnetic anisotropy. We find that the variation in the depinning field under current is strongly dependent on the direction of propagation of the domain wall. This asymmetry arises from the stray dipolar fields generated by the reference layer, which plays an important role in influencing the magnetization reversal process under current. In particular, it can favor a nucleation process instead of domain wall motion, which may be amplified by the current.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
75.47.Np Metals and alloys

Switching of saturation magnetization by carrier injection in YBa2Cu3O7−δ/α-Fe2O3/Nb–SrTiO3 junctions

Yuansha Chen, Guijun Lian, Guangcheng Xiong, and T. Venkatesan

Appl. Phys. Lett. 98, 232513 (2011); http://dx.doi.org/10.1063/1.3589351 (3 pages) | Cited 3 times

Online Publication Date: 10 June 2011

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Ferromagnetic (FM) α-Fe2O3 layers were deposited on n-type oxide semiconductor substrates of Nb-doped SrTiO3 (NSTO) to form YBa2Cu3O7−δ/α-Fe2O3/NSTO junctions. Multilevel resistance switching behavior was observed in YBa2Cu3O7−δ/α-Fe2O3/NSTO junctions with stable resistive states. The saturation magnetization MS of the YBa2Cu3O7−δ/α-Fe2O3/NSTO junctions was modulated by carrier injection and correlated with the conductivity of the switched state. This is the first report of simultaneous modulation of intrinsic magnetic and transport properties for FM oxide devices by using carrier injection.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.78.-n Magnetization dynamics
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