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9 May 2005

Volume 86, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 86, 191102 (2005); http://dx.doi.org/10.1063/1.1922084 (3 pages)

Nir Dahan, Avi Niv, Gabriel Biener, Vladimir Kleiner, and Erez Hasman
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Interlayer coupling in a trilayer junction having bismuth as spacer layer

Jen-Hwa Hsu and D. R. Sahu

Appl. Phys. Lett. 86, 192501 (2005); http://dx.doi.org/10.1063/1.1925323 (3 pages) | Cited 3 times

Online Publication Date: 2 May 2005

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A trilayer system (CoFe/Bi/Co) with bismuth as a spacer layer was synthesized using dc sputtering at room temperature. Magnetization studies show that the interlayer coupling between two ferromagnetic electrodes oscillates with the thickness of Bi spacer layer at room temperature, as seen in most metallic spacers, but it has a much longer period, which is estimated to be 180 to 200 Å. Furthermore, the range of interlayer coupling between two ferromagnetic layers separated by Bi spacer can be extended up to 500 Å. As the measuring temperature is reduced, the strength of interlayer coupling increases and varies with Bi thickness in a similar way, but the oscillation amplitude decreases.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Low-resistance magnetic tunnel junctions prepared by partial remote plasma oxidation of 0.9 nm Al barriers

Ricardo Ferreira, Paulo P. Freitas, Maureen MacKenzie, and John N. Chapman

Appl. Phys. Lett. 86, 192502 (2005); http://dx.doi.org/10.1063/1.1925318 (3 pages) | Cited 6 times

Online Publication Date: 2 May 2005

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Current perpendicular to the plane read-head elements suitable for high-density magnetic storage require low resistance while maintaining a reasonable magnetoresistive (MR) signal (R×A<1 Ω μm2 and MR>20% for areal densities >200 Gb/in2). This letter shows that competitive low R×A junctions can be produced using underoxidized barriers starting from 0.9 nm thick Al layers. For as-deposited junctions, tunneling magnetoresistance (TMR) ∼ 20% for R×A ∼ 2–15 Ω μm2 is obtained, while in the R×A ∼ 60–150 Ω μm2 range, TMR values between 40% to 45% are achieved. A limited number of junctions exhibits considerably lower R×A values with respect to the average, while keeping a similar MR (down to 0.44 Ω μm2 with TMR of 20% and down to 2.2 Ω μm2 with TMR of 52%). Experimental data suggest that current confinement to small regions (barrier defects/hot spots) may explain these results.
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75.47.Np Metals and alloys
75.50.Ss Magnetic recording materials
81.65.Mq Oxidation
52.77.-j Plasma applications

Magnetic domain configurations in spark-eroded ferromagnetic shape memory Ni-Mn-Ga particles

Virgil C. Solomon, Martha R. McCartney, David J. Smith, YunJun Tang, Ami E. Berkowitz, and Robert C. O’Handley

Appl. Phys. Lett. 86, 192503 (2005); http://dx.doi.org/10.1063/1.1925319 (3 pages) | Cited 15 times

Online Publication Date: 2 May 2005

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Spherical particles of the ferromagnetic shape memory material Ni51Mn29Ga20 obtained by spark erosion transform during cooling from the high-temperature Heusler L21 cubic phase into tetragonal martensite. Using the Fresnel (i.e., Lorentz) imaging mode, magnetic domains with an average width of 100 nm are observed in the modulated martensitic phase in the absence of a magnetic field. The magnetization distribution within individual particles is determined using electron holography. The magnetic flux lines change direction when crossing boundaries between crystallographic twin variants. These boundaries, where the easy c-axis of the crystallographic variants rotate by 86.5°, coincide with quasi-90° magnetic domain walls, with thickness of approximately 17 nm. The magnetization saturation determined by electron holography is about 0.57 T.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ch Domain walls and domain structure
81.30.Kf Martensitic transformations
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
64.70.K- Solid-solid transitions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Mm Grain and twin boundaries

Impact of niobium doping upon the magnetotransport properties of the oxygen-deficient perovskite SrCo1−xNbxO3−δ

T. Motohashi, V. Caignaert, V. Pralong, M. Hervieu, A. Maignan, and B. Raveau

Appl. Phys. Lett. 86, 192504 (2005); http://dx.doi.org/10.1063/1.1925312 (3 pages) | Cited 3 times

Online Publication Date: 3 May 2005

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The oxygen-deficient perovskite cobaltite SrCo1−xNbxO3−δ was synthesized by direct solid-state reaction and its magnetotransport properties were investigated. This cobaltite exhibits an unusual ferromagnetic behavior with a transition temperature Tm = 130 to 150 K and a spin-glass-like behavior below Tm. Importantly, this phase reaches a large magnetoresistance (MR) value, MR ≡ −(ρH−ρ0)/ρ0 = 30% at 5 K in 7 T. The large MR effect is believed to be related to the disordered magnetic state induced by the Nb-for-Co substitution.
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75.47.Pq Other materials
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.up Other materials
75.50.Lk Spin glasses and other random magnets

Ru-doped La0.6Sr0.4MnO3 thin films as a coercivity tunable electrode for magnetic tunnel junctions

Hiroyuki Yamada, M. Kawasaki, and Y. Tokura

Appl. Phys. Lett. 86, 192505 (2005); http://dx.doi.org/10.1063/1.1923199 (3 pages) | Cited 16 times

Online Publication Date: 3 May 2005

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We have fabricated the epitaxial thin films of La1−xSrxMn1−yRuyO3 (x = 0.4, y = 0, 0.05, and 0.1) with an atomically flat surface by a pulsed-laser deposition method. The Ru doping enhances the coercive field from 40 Oe (y = 0) to 300 Oe (y = 0.05) and 600 Oe (y = 0.1) at 5 K. The moderate Ru doping (y = 0.05) even increases the ferromagnetic transition temperature from 340 to 355 K, while hardly affecting the highly metallic conductivity. In these remarkable features, important roles may be played by the charge-transfer reaction of Mn4++Ru4+→Mn3++Ru5+, where Mn ferromagnetic spins are coupled antiferromagnetically with Ru spins showing a large single-ion anisotropy.
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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
75.50.Ee Antiferromagnetics
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
61.72.up Other materials
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Influence of the lateral movement on the levitation and guidance force in the high-temperature superconductor maglev system

Honghai Song, Oliver de Haas, Christoph Beyer, Gernot Krabbes, Peter Verges, and Ludwig Schultz

Appl. Phys. Lett. 86, 192506 (2005); http://dx.doi.org/10.1063/1.1923190 (3 pages) | Cited 13 times

Online Publication Date: 4 May 2005

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After the levitation force relaxation was studied for different field-cooling height and working-levitation height, the high-temperature superconductor (HTS) bulk was horizontally moved in the lateral direction above the permanent magnet guideway. Both levitation and guidance force were collected by the measurement system at the same time. It was found that the decay of levitation force is dependent on both the maximum lateral displacement and the movement cycle times, while the guidance force hysteresis curve does not change after the first cycle. This work provided scientific analysis for the HTS maglev system design.
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74.72.-h Cuprate superconductors
84.71.Ba Superconducting magnets; magnetic levitation devices
85.25.Am Superconducting device characterization, design, and modeling
85.70.Rp Magnetic levitation, propulsion and control devices

Microcrack-free epitaxy of thick YBa2Cu3O7−δ films on vicinal r-cut sapphire buffered with CeO2

J. C. Nie, H. Yamasaki, Y. Nakagawa, K. Develos-Bagarinao, M. Murugesan, H. Obara, and Y. Mawatari

Appl. Phys. Lett. 86, 192507 (2005); http://dx.doi.org/10.1063/1.1926415 (3 pages) | Cited 9 times

Online Publication Date: 4 May 2005

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YBa2Cu3O7−δ (YBCO) films were fabricated by pulsed laser deposition on deliberately miscut Al2O3(1math02) buffered with CeO2. Scanning electron microscopy observations demonstrated that 1-μm-thick YBCO films were microcrack free. Characterization of the films revealed porous morphology and high crystalline quality of YBCO with CuO planes tilted vertically and terminated frequently. These features are considered to be a contributing factor to the strain-relieving mechanism responsible for the increase in film thickness without microcracking. Microcrack-free thick YBCO films revealed Tc = 90.5±0.5 K, Jc (77.3 K, 0 T) = 2.0–3.0×106 A/cm2, and a substantial enhancement of Jc×t (77.3 K, 0 T) up to 246 A/cm.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.25.Ld Mechanical and acoustical properties, elasticity, and ultrasonic attenuation
68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
61.43.Gt Powders, porous materials
81.05.Rm Porous materials; granular materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.47.Gh Oxide surfaces

The effect of growth rates on the microstructures of EuBa2Cu3O7−x films on SrTiO3 substrates

Y. Lin, H. Wang, M. E. Hawley, S. R. Foltyn, and Q. X. Jia

Appl. Phys. Lett. 86, 192508 (2005); http://dx.doi.org/10.1063/1.1906312 (3 pages) | Cited 1 time

Online Publication Date: 4 May 2005

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We report our detailed studies of the microstructures of EuBa2Cu3O7−x (Eu123) films by using high-resolution x-ray diffraction. Reciprocal space maps show that the growth rate plays an important role in nucleation of a-axis Eu123 films on SrTiO3 (STO) substrates at a given deposition temperature. It is further revealed that a pseudotetragonal distortion often occurs in Eu123 films. This distortion, however, can be eliminated by decreasing the deposition rate. The low mobility of Eu atoms on the STO substrate is suggested to be the main reason for these phenomena.
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74.78.-w Superconducting films and low-dimensional structures
68.55.A- Nucleation and growth
68.60.Wm Other nonelectronic physical properties

Selective epitaxial growth of submicron complex oxide structures by amorphous SrTiO3

P. Morales, M. DiCiano, and J. Y. T. Wei

Appl. Phys. Lett. 86, 192509 (2005); http://dx.doi.org/10.1063/1.1925781 (3 pages) | Cited 3 times

Online Publication Date: 5 May 2005

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A chemical-free technique for fabricating submicron complex oxide structures has been developed based on selective epitaxial growth. The crystallinity and hence the conductivity of the complex oxide is inhibited by amorphous SrTiO3 (STO). Using a combination of pulsed laser deposition and electron-beam lithography, amorphous STO barriers are first deposited on a single-crystal substrate. A thin film is then deposited on the patterned substrate with the amorphous STO barriers acting to electrically and physically isolate different regions of the film. Since no chemical or physical etchants come in contact with the deposited film, its integrity and stability are preserved. This technique has produced submicron YBa2Cu3O7−δ and La2/3Ca1/3MnO3 structures.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
74.72.-h Cuprate superconductors
81.16.Nd Micro- and nanolithography
75.50.Dd Nonmetallic ferromagnetic materials
68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition
61.46.-w Structure of nanoscale materials

Néel temperature enhancement in nanostructured nickel zinc ferrite

N. Ponpandian, A. Narayanasamy, C. N. Chinnasamy, N. Sivakumar, J.-M. Greneche, K. Chattopadhyay, K. Shinoda, B. Jeyadevan, and K. Tohji

Appl. Phys. Lett. 86, 192510 (2005); http://dx.doi.org/10.1063/1.1925755 (3 pages) | Cited 34 times

Online Publication Date: 5 May 2005

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The Néel temperature of Ni0.5Zn0.5Fe2O4 spinel ferrite increases significantly from 538 K in the bulk state to 592 K when the grain size is reduced to 16 nm by milling in a high-energy ball mill. This has been attributed to an increase in the AB superexchange interaction strength due to a possible enhancement in the magnetic ion concentration in the A-site on milling, as is evident from extended x-ray absorption fine structure and in-field Mössbauer measurements.
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75.50.Gg Ferrimagnetics
81.07.Bc Nanocrystalline materials
75.30.Et Exchange and superexchange interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order
61.46.-w Structure of nanoscale materials
78.70.Dm X-ray absorption spectra
76.80.+y Mössbauer effect; other γ-ray spectroscopy
81.20.Wk Machining, milling

Effects of temperature on good rectifying characteristic of manganite-based p‐n junction

Tian-Yi Cai and Zhen-Ya Li

Appl. Phys. Lett. 86, 192511 (2005); http://dx.doi.org/10.1063/1.1923171 (3 pages) | Cited 5 times

Online Publication Date: 5 May 2005

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The good rectifying characteristic of manganite-based p‐n junction are reproduced. Different from conventional p‐n junctions, the variation of electronic structure of doped manganite with temperature is considered. It is obtained that the diffusion potential of a manganite-based p‐n junction decreases with the increasing temperature. It is in good agreement with experimental results.
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73.40.Ei Rectification
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.20.Ps Other inorganic compounds
66.30.H- Self-diffusion and ionic conduction in nonmetals
75.30.Et Exchange and superexchange interactions

An interface-proximity model for switchable interfacial uncompensated antiferromagnetic spins and their role in exchange bias

Ki-Suk Lee, Young-Sang Yu, and Sang-Koog Kim

Appl. Phys. Lett. 86, 192512 (2005); http://dx.doi.org/10.1063/1.1920412 (3 pages) | Cited 4 times

Online Publication Date: 5 May 2005

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We propose an interface-proximity model that allows us to solve a longstanding puzzle regarding large discrepancies between the experimentally observed and theoretically estimated values of exchange-bias field Heb in coupled ferromagnetic∕antiferromagnetic (F∕AF) metallic films. In this proposed model, switchable uncompensated (UC) AF spins in contact with an F layer are taken into account as an additionally inserting layer that is chemically or magnetically distinguishable from each of the nominal AF and F layers. Reductions in Heb, enhancements in coercivity, and other exchange-bias behaviors typically observed in experiments are very well reproduced from this model. The switchable interfacial UC region with a sizable thickness, heretofore ignored, plays a crucial role in the exchange bias phenomenon.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Structural stability and magnetic properties of SmCo7−xGax

Yongquan Guo, Wei Li, Weichun Feng, Jun Luo, Jingkui Liang, Qijun He, and Xiaojun Yu

Appl. Phys. Lett. 86, 192513 (2005); http://dx.doi.org/10.1063/1.1926416 (3 pages) | Cited 31 times

Online Publication Date: 5 May 2005

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We have studied the structural stability and magnetic properties of SmCo7−xGax compounds using powder x-ray diffraction and magnetic measurements. Gallium as a dopant not only stabilizes the SmCo 1:7 phase but also induces a strong uniaxial magnetocrystalline anisotropy. An anisotropy field as high as 30.7 T is observed at 5 K in the SmCo6Ga compound. The strong anisotropy field might be due to the occupation of Ga atom. The structural stability of SmCo7−xGax compounds is related to the effective Sm/(Co,Ga) atomic radius ratio (RA) and the difference in electronegativity (XA) between Sm and (Co,Ga). According to our calculation, the SmCo 1:7 type structure can be stabilized in range from 1.08(5) to 1.12(9) for RA and −1.04(4) to −0.94(4) for XA.
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75.50.Ww Permanent magnets
75.30.Gw Magnetic anisotropy

Diversity of the magnetic coupling behaviors in the CoFe2/CoFe2O4 system

N. Viart, R. Sayed Hassan, C. Mény, P. Panissod, C. Ulhaq-Bouillet, J. L. Loison, G. Versini, F. Huber, and G. Pourroy

Appl. Phys. Lett. 86, 192514 (2005); http://dx.doi.org/10.1063/1.1923763 (3 pages) | Cited 8 times

Online Publication Date: 6 May 2005

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The CoFe2/CoFe2O4 system has been considered for use as hard electrodes in spin valve devices. In this letter, we focus on the nature and intensity of the magnetic exchange coupling between the two phases. CoFe2/CoFe2O4 and CoFe2O4/CoFe2 bilayers were fabricated by pulsed laser deposition from a metallic CoFe2 alloy target in a vacuum and in an O2:N2 oxidizing atmosphere for the metallic and oxide layers, respectively. Depending upon the elaboration conditions, three different coupling behaviors have been observed: Ferromagnetic, biquadratic, and antiferromagnetic. The minor loop shift and the apparent coercive field of the metal observed in the first two cases are of several hundreds of Oe for a metal thickness of 10 nm. Those very large loop shifts and coercive fields confirm the potential usefulness of this system in terms of applications.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
75.30.Et Exchange and superexchange interactions
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.70.Gm Exchange interactions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Fg Pulsed laser ablation deposition
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.50.Gg Ferrimagnetics

Spin transfer in antisymmetric exchange-biased spin-valves

Y. Jiang, G. H. Yu, Y. B. Wang, J. Teng, T. Ochiai, N. Tezuka, and K. Inomata

Appl. Phys. Lett. 86, 192515 (2005); http://dx.doi.org/10.1063/1.1927694 (3 pages) | Cited 9 times

Online Publication Date: 6 May 2005

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In this letter, we report on measurements of current-induced magnetization switching (CIMS) in current-perpendicular-to-plane exchange-biased spin-valves (ESPVs). The structures of the ESPVs are all “antisymmetric,” but with different thickness of a ruthenium (Ru) layer. It is confirmed that the “antisymmetric” structures largely enhance the spin transfer effect and therefore reduce critical current densities for the CIMS. The effect of the Ru layer on the spin transfer in the ESPVs is also systematically studied. With a decrease of the Ru layer’s thickness, the critical current densities can be further reduced. The lowest critical current we achieved in an “antisymmetric” structure is 1×106 A/cm2, which realizes a reduction of more than one order of magnitude compared with all the reported works.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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