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8 May 2006

Volume 88, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 88, 193113 (2006); http://dx.doi.org/10.1063/1.2202003 (3 pages)

Fa-Quan He and Ya-Pu Zhao
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Magnetic properties and microstructures of FePt/Ti bilayer films sputter deposited onto glass amorphous substrates

H. Y. Sun, J. L. Xu, S. Z. Feng, Z. F. Su, J. Hu, and Y. P. Sun

Appl. Phys. Lett. 88, 192501 (2006); http://dx.doi.org/10.1063/1.2195781 (3 pages) | Cited 6 times

Online Publication Date: 8 May 2006

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FePt/Ti granular films were fabricated onto glass amorphous substrates using a dc facing-target magnetron sputtering system at various Ti underlayer thickness, then annealed at temperature Ta ranging from 200 to 700 °C. In the FePt (30 nm)/Ti (1 nm) film annealed at 600 °C, the coercivity about 12 kOe is obtained. The results of x-ray diffraction indicate that a ternary FePtTi alloy is formed. Thus, the formation of the ternary FePtTi alloy is considered to play an important role in magnetic properties.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Carrier-mediated ferromagnetism in vanadium-doped (Sb1−xBix)2Te3 solid solutions

Zhenhua Zhou, Ctirad Uher, Marek Zabcik, and Petr Lostak

Appl. Phys. Lett. 88, 192502 (2006); http://dx.doi.org/10.1063/1.2200738 (3 pages) | Cited 1 time

Online Publication Date: 8 May 2006

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Ferromagnetism in tetradymite-type diluted magnetic semiconductors (Sb1−xBix)1.98V0.02Te3 (0 ⩽ x ⩽ 1) is revealed to be of hole-mediated nature. The increasing replacement of antimony with bismuth results in a monotonous decrease of the hole concentration and the Curie temperature while the electrical resistivity increases. The value of the Curie temperature shows a linear dependence of Np1/3, where N is the vanadium concentration and p is the concentration of hole. This trend agrees with the mean-field theory predictions.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.S- Impurities in crystals
61.72.up Other materials

Field-induced percolation transition and 100% low-field magnetoresistance in aligned half-metallic nanoparticle arrays

Tian-Yi Cai, Sheng Ju, and Zhen-Ya Li

Appl. Phys. Lett. 88, 192503 (2006); http://dx.doi.org/10.1063/1.2202103 (3 pages) | Cited 6 times

Online Publication Date: 9 May 2006

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A Monte Carlo simulation is performed to study the relationship between magnetization reversal and magnetotransport in half-metallic nanoparticle arrays. It is found that both the absolute magnitude of low-field magnetoresistance and the switching effect are significantly enhanced when the magnetic anisotropic axes of nanoparticles are aligned along the same direction. Compared with conventional granular ferromagnets, a percolation mechanism is found to dominate, leading to a 100% low-field magnetoresistance in two-dimensional half-metallic nanoparticle arrays. These results also give a deeper insight into the experimental findings, where optimized magnetoresistive effects are found in CrO2 composites with field-aligned CrO2 particles.
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75.47.Pq Other materials
64.60.A- Specific approaches applied to studies of phase transitions
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials

Robust Ti4+ states in SrTiO3 layers of La0.6Sr0.4MnO3/SrTiO3/La0.6Sr0.4MnO3 junctions

H. Kumigashira, A. Chikamatsu, R. Hashimoto, M. Oshima, T. Ohnishi, M. Lippmaa, H. Wadati, A. Fujimori, K. Ono, M. Kawasaki, and H. Koinuma

Appl. Phys. Lett. 88, 192504 (2006); http://dx.doi.org/10.1063/1.2202118 (3 pages) | Cited 20 times

Online Publication Date: 9 May 2006

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We have investigated the interfacial electronic structure of La0.6Sr0.4MnO3 (LSMO)/SrTiO3 (STO)/LSMO heterojunctions utilizing the elemental selectivity of photoemission spectroscopy. The Ti 2p core-level spectra clearly show Ti4+ states and do not exhibit any indication of Ti3+ states in TiO2 layers irrespective of a different kind of adjacent atomic layer with different chemical carrier concentration. This result indicates that the Ti ions in the TiO2 atomic layers preserve their tetravalent states even in the vicinity of the valence-mismatched interface between LSMO and STO, reflecting the chemical stability of the Ti4+ states.
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73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
79.60.Jv Interfaces; heterostructures; nanostructures

Monodispersed and highly ordered L10 FePt nanoparticles prepared in the gas phase

Jiao-Ming Qiu and Jian-Ping Wang

Appl. Phys. Lett. 88, 192505 (2006); http://dx.doi.org/10.1063/1.2202130 (3 pages) | Cited 31 times

Online Publication Date: 9 May 2006

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We report the direct preparation of monodispersed L10 phase FePt nanoparticles by controlled nucleation and growth using a gas phase aggregation source. These FePt nanoparticles became ordered during their growth in an argon gas flow. They are octahedron faceted with an average size of 5.8 nm and a standard size distribution of 11%, as illustrated by transmission electron microscope. Magnetic measurements show that these FePt nanoparticles have coercivities of 8.25 kOe at room temperature and 26.5 kOe at 50 K. This technique provides a novel approach for fabricating nanomaterials with controllable phase and shape in general.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.07.Bc Nanocrystalline materials
81.07.Wx Nanopowders
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Surface electronic structure in transition-metal (Cr and Mn) doped GaAs (001) studied by in situ photoemission spectroscopy

K. Kanai, J. Okabayashi, S. Toyoda, M. Oshima, and K. Ono

Appl. Phys. Lett. 88, 192506 (2006); http://dx.doi.org/10.1063/1.2202388 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2006

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As 3d and Ga 3d photoemission spectra were probed in order to investigate the surface states in transition-metal doped GaAs (001) as spintronics materials. The growth mechanism and chemical bonding states at the surface of III–V-based diluted magnetic semiconductors, Ga1−xMnxAs and Ga1−xCrxAs, have been investigated by angular-dependent in situ photoemission spectroscopy. On low-temperature GaAs grown at 200 °C, the difference in core-level photoemission spectra of Ga1−xMnxAs and Ga1−xCrxAs is well related to that in the reflection high-energy electron-diffraction patterns, suggesting that not only As ions but also Ga ions are modulated in Ga1−xMnxAs.
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81.05.Ea III-V semiconductors
73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
75.50.Pp Magnetic semiconductors

Current-driven microwave oscillations in current perpendicular-to-plane spin-valve nanopillars

Q. Mistral, Joo-Von Kim, T. Devolder, P. Crozat, C. Chappert, J. A. Katine, M. J. Carey, and K. Ito

Appl. Phys. Lett. 88, 192507 (2006); http://dx.doi.org/10.1063/1.2201897 (3 pages) | Cited 23 times

Online Publication Date: 9 May 2006

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We study the current and temperature dependences of the microwave voltage emission of spin-valve nanopillars subjected to an in-plane magnetic field and a perpendicular-to-plane current. Despite the complex multilayer geometry, clear microwave emission is observed for current densities in the interval of 9×107–13×107 A cm−2. The emission frequency stays near 12 GHz when I<Ired = 11.2×107 A cm−2, then redshifts with a slope gradually reaching −350 MHz/mA for 16×107 A cm−2. The linewidth narrows exponentially to 3.8 MHz at 150 K for I<Ired, then broadens again as the emitted voltage redshifts. The temperature dependence of the linewidth exhibits a curvature change around the linewidth minimum.
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72.30.+q High-frequency effects; plasma effects
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.47.Np Metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Jk Magnetization reversal mechanisms

Giant tunneling magnetoresistance in Co2MnSi/Al–O/Co2MnSi magnetic tunnel junctions

Y. Sakuraba, M. Hattori, M. Oogane, Y. Ando, H. Kato, A. Sakuma, T. Miyazaki, and H. Kubota

Appl. Phys. Lett. 88, 192508 (2006); http://dx.doi.org/10.1063/1.2202724 (3 pages) | Cited 224 times

Online Publication Date: 10 May 2006

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Magnetic tunnel junctions (MTJs) with a stacking structure of Co2MnSi/Al–O/Co2MnSi were fabricated using magnetron sputtering system. Fabricated MTJ exhibited an extremely large tunneling magnetoresistance (TMR) ratio of 570% at low temperature, which is the highest TMR ratio reported to date for an amorphous Al–O tunneling barrier. The observed dependence of tunneling conductance on bias voltage clearly reveals the half-metallic energy gap of Co2MnSi. The origins of large temperature dependence of TMR ratio were discussed on the basis of the present results.
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75.47.De Giant magnetoresistance
75.47.Np Metals and alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Cd Deposition by sputtering
71.20.Gj Other metals and alloys
75.50.Cc Other ferromagnetic metals and alloys

Antiferromagnetic coupling and enhanced magnetization in all-ferromagnetic superlattices

P. Padhan, W. Prellier, and R. C. Budhani

Appl. Phys. Lett. 88, 192509 (2006); http://dx.doi.org/10.1063/1.2202690 (3 pages) | Cited 19 times

Online Publication Date: 11 May 2006

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The structural and magnetic properties of a series of superlattices consisting of two ferromagnetic metals La0.7Sr0.3MnO3 (LSMO) and SrRuO3 (SRO) grown on (001) oriented SrTiO3 are studied. Superlattices with a fixed LSMO layer thickness of 20 unit cells and varying SRO layer thickness show a sudden drop in magnetization on cooling through a temperature where both LSMO and SRO layers are ferromagnetic. This behavior suggests an antiferromagnetic coupling between the layers. In addition, the samples having thinner SRO layers (n<6) exhibit enhanced saturation magnetization at 10 K. These observations are attributed to the possible modification in the stereochemistry of the Ru and Mn ions in the interfacial region.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics

Orthogonal exchange bias field directions in exchange bias microstructures

P. Candeloro, H. Schultheiß, H. T. Nembach, B. Hillebrands, S. Trellenkamp, C. Dautermann, and S. Wolff

Appl. Phys. Lett. 88, 192510 (2006); http://dx.doi.org/10.1063/1.2202743 (3 pages) | Cited 1 time

Online Publication Date: 11 May 2006

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We report on the realization of microstructures exhibiting the coexistence of two exchange bias fields with orthogonal directions. The microstructures are made of Fe50Mn50/Ni81Fe19 bilayers and have L-like and crosslike shapes. Above the Néel temperature the magnetic elements are initially saturated along the diagonal of the structures and then cooled down in zero external field. This causes the exchange bias field to be initialized along two different axes. Magneto-optical measurements confirm the simultaneous presence of orthogonal biasing directions.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
78.20.Ls Magneto-optical effects

Magnetocaloric properties of Ni2Mn1−xCuxGa

Shane Stadler, Mahmud Khan, Joseph Mitchell, Naushad Ali, Angelo M. Gomes, Igor Dubenko, Armando Y. Takeuchi, and Alberto P. Guimarães

Appl. Phys. Lett. 88, 192511 (2006); http://dx.doi.org/10.1063/1.2202751 (3 pages) | Cited 69 times

Online Publication Date: 11 May 2006

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We present the magnetocaloric properties of the substituted Heusler alloy Ni2Mn1−xCuxGa, which shows a maximum magnetic entropy change of ΔSM ≈ −64 J/Kg K = −532 mJ/cm3 K at 308 K for a magnetic field change ΔH = 5 T. The dependence of ΔSM on ΔH is approximately linear and does not reach saturation at 5 T. It is demonstrated that the temperature at which ΔSM occurs can be tuned through subtle variations in composition.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
65.40.G- Other thermodynamical quantities

Strong pinning enhancement in MgB2 using very small Dy2O3 additions

S. K. Chen, M. Wei, and J. L. MacManus-Driscoll

Appl. Phys. Lett. 88, 192512 (2006); http://dx.doi.org/10.1063/1.2203209 (3 pages) | Cited 40 times

Online Publication Date: 11 May 2006

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0.5–5.0 wt % Dy2O3 was in situ reacted with Mg+B to form pinned MgB2. While Tc remained largely unchanged, Jc was strongly enhanced. The best sample (only 0.5 wt % Dy2O3) had a Jc ∼ 6.5×105 A cm−2 at 6 K, 1 T and 3.5×105 A cm−2 at 20 K, 1 T, around a factor of 4 higher compared to the pure sample, and equivalent to hot-pressed or nano-Si-added MgB2 at ⩽ 1 T. Even distributions of nanoscale precipitates of DyB4 and MgO were observed within the grains. The room temperature resistivity decreased with Dy2O3 indicative of improved grain connectivity.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.Na Mesoscopic and nanoscale systems
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.F- Transport properties

Metamagnetic shape memory effect in a Heusler-type Ni43Co7Mn39Sn11 polycrystalline alloy

R. Kainuma, Y. Imano, W. Ito, H. Morito, Y. Sutou, K. Oikawa, A. Fujita, K. Ishida, S. Okamoto, O. Kitakami, and T. Kanomata

Appl. Phys. Lett. 88, 192513 (2006); http://dx.doi.org/10.1063/1.2203211 (3 pages) | Cited 100 times

Online Publication Date: 11 May 2006

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Shape memory and magnetic properties of a Ni43Co7Mn39Sn11 Heusler polycrystalline alloy were investigated by differential scanning calorimetry, the sample extraction method, and the three-terminal capacitance method. A unique martensitic transformation from the ferromagnetic parent phase to the antiferromagneticlike martensite phase was detected and magnetic-field-induced “reverse” transition was confirmed in a high magnetic field. In addition, a large magnetic-field-induced shape recovery strain of about 1.0% was observed to accompany reverse martensitic transformation, and the metamagnetic shape memory effect, which was firstly reported in a Ni45Co5Mn36.7In13.3 Heusler single crystal, was confirmed in a polycrystalline specimen.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.30.Kf Martensitic transformations

Low field magnetotransport properties of (La0.7Sr0.3MnO3)0.5:(ZnO)0.5 nanocomposite films

B. S. Kang, H. Wang, J. L. MacManus-Driscoll, Y. Li, Q. X. Jia, I. Mihut, and J. B. Betts

Appl. Phys. Lett. 88, 192514 (2006); http://dx.doi.org/10.1063/1.2197317 (3 pages) | Cited 22 times

Online Publication Date: 11 May 2006

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(La0.7Sr0.3MnO3)0.5:(ZnO)0.5 nanocomposite thin films were deposited on c-cut sapphire substrates via pulsed laser deposition. The as-grown films were composed of fine grains of 20–50 nm size. The epitaxial orientation relationships between the La0.7Sr0.3MnO3 (LSMO) and the sapphire was (111)LSMO//(0003)Al2O3 and 〈11math〉LSMO//〈10math0〉Al2O3. A low field magnetoresistance (LFMR) of ∼ 12% was achieved at an external magnetic field of H = 1 T at 77 K, possibly due to enhanced grain boundary effects. The postannealed film had columnar structures with well-crystallized large grains ( ∼ 200 nm), and showed a low resistivity and consequently negligible LFMR similar to that of single crystal LSMO.
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75.47.Lx Magnetic oxides
75.47.Gk Colossal magnetoresistance
61.72.Mm Grain and twin boundaries

Switching spin valves using rf currents

K. Rivkin and J. B. Ketterson

Appl. Phys. Lett. 88, 192515 (2006); http://dx.doi.org/10.1063/1.2199456 (3 pages) | Cited 9 times

Online Publication Date: 12 May 2006

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We show that magnetization reversal in spin-injection devices can be significantly faster when using a chirped rf current, rather than a dc, pulse. Although one can use a simple sinusoidal rf pulse, an optimized series of alternating, equal-amplitude, pulses of varying width (a digitized approximation to a chirped rf pulse) produces more efficient switching.
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75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.-b Spin polarized transport
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