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14 Feb 2005

Volume 86, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 86, 071101 (2005); http://dx.doi.org/10.1063/1.1862756 (3 pages)

Robert Horvath, Henrik C. Pedersen, Nina Skivesen, David Selmeczi, and Niels B. Larsen
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Reversal behavior of exchange-biased submicron dots

Zhi-Pan Li, Oleg Petracic, Johannes Eisenmenger, and Ivan K. Schuller

Appl. Phys. Lett. 86, 072501 (2005); http://dx.doi.org/10.1063/1.1863449 (3 pages) | Cited 21 times

Online Publication Date: 7 February 2005

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Nanostructured Fe dots were prepared on antiferromagnetic FeF2 thin films and investigated by magneto-optical Kerr effect (MOKE). We studied the influence of dot sizes on the magnetic hysteresis and compared the result with both continuous thin film bilayers and nanostructured Fe/FeF2 pillars. Hysteresis loops were measured at temperatures below and above (10 and 90 K, respectively) the Néel temperature of the antiferromagnet. A vortex state is found for dots of 300 nm diameter, where the exchange bias field is reduced compared to larger dot system and the continuous bilayer. Micromagnetic simulations including the interaction with the antiferromagnet show qualitatively similar behavior.
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75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films
75.75.-c Magnetic properties of nanostructures
75.60.Jk Magnetization reversal mechanisms
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
78.20.Ls Magneto-optical effects

Transmission of single-flux-quantum pulse between superconductor chips

Yoshihito Hashimoto, Shinichi Yorozu, and Toshiyuki Miyazaki

Appl. Phys. Lett. 86, 072502 (2005); http://dx.doi.org/10.1063/1.1864239 (3 pages) | Cited 5 times

Online Publication Date: 7 February 2005

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Single-flux-quantum (SFQ) pulse transmission between superconductor chips mounted on a passive microstrip carrier is reported. In contrast to the earlier work based on a double-flux-quantum (DFQ) driver, we used an SFQ driver; that is, the simplest driver. To deal with transmission loss at solder-bump bonds, we improved the receiver’s sensitivity by reducing its critical current, and optimized the SFQ driver to have as large an output amplitude as possible with a sufficient bias margin. Chip-to-chip transmission on a passive microstrip carrier with 50 μm solder-bump bonds up to 60 Gbps has been achieved at a junction critical current density of 2.5 KA/cm2.
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85.25.Cp Josephson devices
85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits
84.40.Az Waveguides, transmission lines, striplines
74.25.Sv Critical currents

Correlations between low-field microwave absorption and magnetoimpedance in Co-based amorphous ribbons

H. Montiel, G. Alvarez, I. Betancourt, R. Zamorano, and R. Valenzuela

Appl. Phys. Lett. 86, 072503 (2005); http://dx.doi.org/10.1063/1.1861959 (3 pages) | Cited 14 times

Online Publication Date: 7 February 2005

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Microwave power absorption measurements at 9.4 GHz were carried out on as-cast amorphous ribbons of nominal composition Co66Fe4B12Si13Nb4Cu. Two absorptions were observed: a small signal at a low dc field (<0.01 T) and another one at a high dc field ( ∼ 0.1682 T). The high-field signal shows all the features corresponding to ferromagnetic resonance. The low-field absorption (LFA) signal exhibits different characteristics such as hysteresis and a minimum in power absorption at zero magnetic field. A correlation between this LFA signal and magnetoimpedance measurements showed that both electromagnetic processes are associated with the same phenomenon.
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75.50.Bb Fe and its alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
72.15.Gd Galvanomagnetic and other magnetotransport effects
78.70.Gq Microwave and radio-frequency interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Np Metals and alloys
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Excellent magnetocaloric properties of La0.7Ca0.3−xSrxMnO3 (0.05 ⩽ x ⩽ 0.25) single crystals

Manh-Huong Phan, Seong-Cho Yu, and Nam Hwi Hur

Appl. Phys. Lett. 86, 072504 (2005); http://dx.doi.org/10.1063/1.1867564 (3 pages) | Cited 39 times

Online Publication Date: 8 February 2005

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This letter reports on the superior magnetocaloric properties of La0.7Ca0.3−xSrxMnO3 (x = 0.05, 0.10, 0.20, and 0.25) single crystals. Upon 50 kOe applied field, the magnetic entropy changes (ΔSM) reach values of ∼ 10.5, 7.45, 6.97, and 6.86 J/kg K for x = 0.05, 0.10, 0.20, and 0.25 compositions, respectively. The large magnetic entropy changes have been found to occur around 300 K, thus allowing magnetic refrigeration at room temperature. Due to the absence of grains in the single crystals, the ΔSM distribution here is much more uniform than that of gadolinium and polycrystalline manganites, which is desirable for an Ericson-cycle magnetic refrigerator. The single crystals have the large magnetic entropy changes induced by low magnetic field change, which is beneficial for the household application of active magnetic refrigerant (AMR) materials. These results indicate that the present single crystals are excellent candidates as working materials for AMR.
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75.50.Dd Nonmetallic ferromagnetic materials
75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
65.40.G- Other thermodynamical quantities
75.60.Nt Magnetic annealing and temperature-hysteresis effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Local environment of ferromagnetically ordered Mn in epitaxial InMnAs

P. T. Chiu, B. W. Wessels, D. J. Keavney, and J. W. Freeland

Appl. Phys. Lett. 86, 072505 (2005); http://dx.doi.org/10.1063/1.1855427 (3 pages) | Cited 10 times

Online Publication Date: 9 February 2005

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The magnetic properties of the ferromagnetic semiconductor In0.98Mn0.02As were characterized by x-ray absorption spectroscopy and x-ray magnetic circular dichroism. The Mn exhibits an atomic-like L2,3 absorption spectrum that indicates that the 3d states are highly localized. In addition, a large dichroism at the Mn L2,3 edge was observed from 5 to 300 K at an applied field of 2T. A calculated spectrum assuming atomic Mn2+ yields the best agreement with the experimental InMnAs spectrum. A comparison of the dichroism spectra of MnAs and InMnAs shows clear differences suggesting that the ferromagnetism observed in InMnAs is not due to hexagonal MnAs clusters. The temperature dependence of the dichroism indicates the presence of two ferromagnetic species, one with a transition temperature of 30 K and another with a transition temperature in excess of 300 K. The dichroism spectra are consistent with the assignment of the low temperature species to random substitutional Mn and the high temperature species to Mn near-neighbor pairs.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
78.70.Dm X-ray absorption spectra

Effects of capping on the Ga1−xMnxAs magnetic depth profile

B. J. Kirby, J. A. Borchers, J. J. Rhyne, K. V. O’Donovan, T. Wojtowicz, X. Liu, Z. Ge, S. Shen, and J. K. Furdyna

Appl. Phys. Lett. 86, 072506 (2005); http://dx.doi.org/10.1063/1.1867292 (3 pages) | Cited 8 times

Online Publication Date: 9 February 2005

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Annealing can increase the Curie temperature and net magnetization in uncapped Ga1−xMnxAs films, effects that are suppressed when the films are capped with GaAs. Previous polarized neutron reflectometry (PNR) studies of uncapped Ga1−xMnxAs revealed a pronounced magnetization gradient that was reduced after annealing. We have extended this study to Ga1−xMnxAs capped with GaAs. We observe no increase in Curie temperature or net magnetization upon annealing. Furthermore, PNR measurements indicate that annealing produces minimal differences in the depth-dependent magnetization, as both as-grown and annealed films feature a significant magnetization gradient. These results suggest that the GaAs cap inhibits redistribution of interstitial Mn impurities during annealing.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.05.Ea III-V semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
61.72.Cc Kinetics of defect formation and annealing
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Rs Electrical and magnetic properties related to treatment conditions
61.72.J- Point defects and defect clusters
61.72.S- Impurities in crystals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Magnetoresistance of single magnetic vortices

P. Vavassori, M. Grimsditch, V. Metlushko, N. Zaluzec, and B. Ilic

Appl. Phys. Lett. 86, 072507 (2005); http://dx.doi.org/10.1063/1.1866212 (3 pages) | Cited 26 times

Online Publication Date: 9 February 2005

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The magnetoresistance in a 1 μm Permalloy disk, that develops a vortex state during reversal, has been experimentally measured and modeled. The agreement between measurements and numerical simulations shows that the conventional anisotropic magnetoresistance effect is the main source of magnetoresistance. The results demonstrate that magnetoresistance can be used to determine the chirality of the vortex thereby improving the chances that patterned dot arrays could be used in data storage technology.
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75.50.Bb Fe and its alloys
75.50.Ss Magnetic recording materials
75.47.Np Metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Electrochemical control and selection of the structural and magnetic properties of cobalt nanowires

M. Darques, L. Piraux, A. Encinas, P. Bayle-Guillemaud, A. Popa, and U. Ebels

Appl. Phys. Lett. 86, 072508 (2005); http://dx.doi.org/10.1063/1.1866636 (3 pages) | Cited 31 times

Online Publication Date: 10 February 2005

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In this letter we present a convenient way of controlling the direction of the uniaxial magnetocrystalline anisotropy in arrays of electrodeposited hcp Co nanowires. Combining electron microscopy and ferromagnetic resonance measurements, it is shown that using an appropriate pH of the electrolytic solution, the hcp c axis can be oriented parallel or perpendicular to the wires axes simply by changing the deposition current density or deposition rate. This reorientation of the c axis leads to a drastic change in overall magnetic anisotropy as the crystal anisotropy either competes for perpendicular oriented c axis or adds to the shape anisotropy for parallel oriented c axis.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
75.30.Gw Magnetic anisotropy
82.45.Yz Nanostructured materials in electrochemistry
61.46.-w Structure of nanoscale materials
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
82.45.Gj Electrolytes
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.37.Lp Transmission electron microscopy (TEM)

Magnetization losses in multifilament coated superconductors

G. A. Levin, P. N. Barnes, N. Amemiya, S. Kasai, K. Yoda, and Z. Jiang

Appl. Phys. Lett. 86, 072509 (2005); http://dx.doi.org/10.1063/1.1861955 (3 pages) | Cited 16 times

Online Publication Date: 10 February 2005

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We report the results of a study of the magnetization losses in experimental multifilament, as well as control (uniform) coated superconductors exposed to time-varying magnetic fields of various frequencies. Both the hysteresis loss, proportional to the sweep rate of the applied magnetic field, and the coupling loss, proportional to the square of the sweep rate, have been observed. A scaling is found that allows us to quantify each of these contributions and extrapolate the results of the experiment beyond the envelope of accessible field amplitude and frequency. The combined loss in the multifilament conductor is reduced by about 90% in comparison with the uniform conductor at full field penetration at a sweep rate as high as 3 T/s.
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74.72.-h Cuprate superconductors
84.71.Mn Superconducting wires, fibers, and tapes
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.25.Ha Magnetic properties including vortex structures and related phenomena

Large low-field magnetoresistance effect in Sr2FeMoO6 homocomposites

Y. H. Huang, J. Lindén, H. Yamauchi, and M. Karppinen

Appl. Phys. Lett. 86, 072510 (2005); http://dx.doi.org/10.1063/1.1864241 (3 pages) | Cited 5 times

Online Publication Date: 10 February 2005

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Homocomposites consisting of two single-phase Sr2FeMoO6 components with different grain sizes were prepared by a sol-gel method. Large low-field magnetoresistance (LFMR) effect was achieved for the composites. Experimental results show that the LFMR strongly depends on both the relative amounts of the two components and their grain sizes. The magnetoresistance value is found to be proportional to the square of the relative magnetization (M/Ms). We suggest that the LFMR enhancement in the homocomposites compared with parent Sr2FeMoO6 has its origin in the enhanced intergranular effects.
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75.50.Dd Nonmetallic ferromagnetic materials
81.05.Mh Cermets, ceramic and refractory composites
72.20.My Galvanomagnetic and other magnetotransport effects
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
61.72.Mm Grain and twin boundaries
75.47.Pq Other materials
72.25.-b Spin polarized transport
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Ferromagnetic properties of epitaxial SrRuO3 films on SiO2/Si using biaxially oriented MgO as templates

B. S. Kang, Jang-Sik Lee, L. Stan, L. Civale, R. F. DePaula, P. N. Arendt, and Q. X. Jia

Appl. Phys. Lett. 86, 072511 (2005); http://dx.doi.org/10.1063/1.1865335 (3 pages) | Cited 3 times

Online Publication Date: 10 February 2005

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We have deposited epitaxial SrRuO3 (SRO) thin films on SiO2/Si substrates using biaxially oriented MgO templates produced by ion-beam-assisted deposition. The strain states of the SRO films are strongly affected by the crystallinity of the templates: the better the in-plane texture of the template is, the more in-plane tensile stress the films are subjected to. On the other hand, SRO films are relatively loosely strained with lattice parameters closer to bulk property if the templates have a broad in-plane alignment. The magnetization of the SRO films is well described by Bloch’s T3/2 law at low temperatures, which is well known as the result of spin wave excitation: M(T)/M(0) = 1−AT3/2. The strained films show larger spin wave parameter A values, reflecting larger magnetization suppression. The suppression of magnetization in the strained films is attributed to the change in the magnetic coupling since this coupling is very sensitive to the interatomic distance.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Ds Spin waves
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
68.60.Bs Mechanical and acoustical properties

All-MgB2 tunnel junctions with aluminum nitride barriers

Hisashi Shimakage, Kazuya Tsujimoto, Zhen Wang, and Masayoshi Tonouchi

Appl. Phys. Lett. 86, 072512 (2005); http://dx.doi.org/10.1063/1.1868871 (3 pages) | Cited 31 times

Online Publication Date: 11 February 2005

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All-MgB2 tunnel junctions were fabricated on a C-plane sapphire substrate. The current-voltage characteristics showed both quasiparticle and Josephson tunneling currents and a clear gap structure. The current density was 115 A/cm2 for a 20×20 μm2 junction with a 0.14-nm-thick AlN layer, and the ratio of the subgap resistance and normal resistance was 3.3. The gap voltages of lower and upper MgB2 electrodes were estimated to be 2.2 and 1.5 mV, respectively. The temperature dependence of the Josephson current indicated that a normal layer existed between the AlN and the MgB2 electrodes. The Josephson tunneling currents were clearly modulated by applying an external magnetic field.
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74.78.Fk Multilayers, superlattices, heterostructures
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.50.+r Tunneling phenomena; Josephson effects
74.25.F- Transport properties
74.25.Sv Critical currents

Enhanced sensitivity due to current redistribution in the Hall effect of semiconductor-metal hybrid structures

Matthias Holz, Oliver Kronenwerth, and Dirk Grundler

Appl. Phys. Lett. 86, 072513 (2005); http://dx.doi.org/10.1063/1.1862326 (3 pages) | Cited 8 times

Online Publication Date: 11 February 2005

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Experimental and theoretical studies have shown that nonmagnetic semiconductor-metal hybrid structures can exhibit a very large magnetoresistance effect, the so-called extraordinary magnetoresistance (EMR) effect. The EMR can be useful in magnetic-field sensors and read heads. We show that the sensitivity of a linear hybrid structure can be further enlarged by using an optimized configuration of current leads and voltage probes. Strikingly, we find that the EMR and the Hall effect cooperate and thereby improve the performance. Our findings also explain the origin of the recently reported sensitivity increase in a nanostructured EMR device obtained via interchanging one lead and one probe [ J. Moussa et al., J. Appl. Phys. 94, 1110 (2003) ].
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72.20.My Galvanomagnetic and other magnetotransport effects
73.43.Qt Magnetoresistance
73.40.Ns Metal-nonmetal contacts
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Room temperature ferromagnetism in bulk Mn-Doped Cu2O

M. Wei, N. Braddon, D. Zhi, P. A. Midgley, S. K. Chen, M. G. Blamire, and J. L. MacManus-Driscoll

Appl. Phys. Lett. 86, 072514 (2005); http://dx.doi.org/10.1063/1.1869547 (3 pages) | Cited 54 times

Online Publication Date: 11 February 2005

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Bulk Mn-doped Cu2O samples were produced by reacting Cu2O and Mn2O3 powders in Ar gas at 650 and 800 °C to give a nominal composition of 1.7 at.% Mn-doped Cu2O. From x-ray energy dispersive spectrum analysis, the actual doping level was lower at 0.3–0.5 at.% Mn. Room temperature ferromagnetism with a coercive field of 50 Oe was found in the 650 °C samples. The Curie temperature (TC) of samples sintered at 650 °C was above 300 K, whereas for 800 °C samples it was 215±5 K. Using the nominal doping level, the magnetization saturation value was calculated to be ∼ 0.4μB/Mn at 10 K.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.S- Impurities in crystals
75.30.Cr Saturation moments and magnetic susceptibilities
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
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