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6 Aug 2007

Volume 91, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 91, 063118 (2007); http://dx.doi.org/10.1063/1.2768861 (3 pages)

Douglas C. Meier, Steve Semancik, Bradley Button, Evgheni Strelcov, and Andrei Kolmakov
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Band structures, magnetic properties, and enhanced magnetoresistance in the high pressure phase of Gd and Y doped two-dimensional perovskite Sr2CoO4 compounds

X. L. Wang, E. Takayama-Muromachi, S. X. Dou, and Z. X. Cheng

Appl. Phys. Lett. 91, 062501 (2007); http://dx.doi.org/10.1063/1.2759273 (3 pages) | Cited 7 times

Online Publication Date: 6 August 2007

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The authors present their studies on the band structures and on the magnetic and magnetotransport properties of the high pressure phase of Sr2−xRExCoO4 [rare earth (RE) = Gd and Y, x = 0.1–0.5] compounds which were synthesized by a high pressure and high temperature technique. The authors found that as x increases, the magnetoresistance {(ρH−ρ0)/ρ0} increases up to −17% at 5 K and 7 T, which is 2.5 times higher than that for undoped Sr2CoO4, although the ferromagnetic transition drops from 255 to 200 K for the Gd doping with x = 0.3. The saturation moments at low temperature are significantly enhanced for the Gd doped Sr2CoO4. Observation of a close correlation between resistance and field revealed a strong spin-dependent tunneling magnetoresistance. First-principles band structure calculations indicate that high spin polarization is present for both undoped and doped compounds.
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75.47.Pq Other materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
71.20.Ps Other inorganic compounds
61.72.up Other materials

Nonreciprocal spin wave spectroscopy of thin Ni–Fe stripes

Pedram Khalili Amiri, Behzad Rejaei, Marina Vroubel, and Yan Zhuang

Appl. Phys. Lett. 91, 062502 (2007); http://dx.doi.org/10.1063/1.2766842 (3 pages) | Cited 8 times

Online Publication Date: 6 August 2007

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The authors report on the observation of nonreciprocal spin wave propagation in a thin ( ∼ 200 nm) patterned Ni–Fe stripe. The spin wave transmission spectrum is measured using a pair of microstrip lines as antennas. The nonreciprocity of surface wave dispersion brought about by an adjacent aluminum ground leads to a nonreciprocal coupling of the antennas. The effects of Ni–Fe film conductivity, thickness, and reflections caused by the lateral confinement of the magnetic stripe are discussed. The nonreciprocity observed in this structure can potentially be used to realize nonreciprocal microwave devices on silicon.
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75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
73.61.At Metal and metallic alloys

Magnetic field effects on the manganite junction with different electronic processes

D. J. Wang, J. R. Sun, Y. W. Xie, W. M. Lü, S. Liang, T. Y. Zhao, and B. G. Shen

Appl. Phys. Lett. 91, 062503 (2007); http://dx.doi.org/10.1063/1.2766847 (3 pages) | Cited 9 times

Online Publication Date: 6 August 2007

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A manganite junction with two distinguishable electronic processes has been fabricated and its rectifying properties are experimentally studied. The current-voltage characteristics of the junctions are found to be dominated by leakage current and thermal current under low and high bias voltages, respectively. The responses of these two processes to magnetic field are found to be different, and the magnetoresistance (MR) of the junction arises mainly from the modification of magnetic field to leakage current. Although the MR shows a monotonic decrease with bias voltage (V), the MR-V dependence is different for the two processes. An approximately linear, yet slow, decrease of MR with V is observed for the leakage process, while an exponential reduction for the thermal one. These results show that the electronic processes undergoing in the junction can be identified based on the analysis of the MR-V relations.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
73.40.Ei Rectification
75.47.Gk Colossal magnetoresistance

Monocrystalline NbN nanofilms on a 3C-SiC/Si substrate

J. R. Gao, M. Hajenius, F. D. Tichelaar, T. M. Klapwijk, B. Voronov, E. Grishin, G. Gol’tsman, C. A. Zorman, and M. Mehregany

Appl. Phys. Lett. 91, 062504 (2007); http://dx.doi.org/10.1063/1.2766963 (3 pages) | Cited 12 times

Online Publication Date: 6 August 2007

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The authors have realized NbN (100) nanofilms on a 3C-SiC (100)/Si(100) substrate by dc reactive magnetron sputtering at 800 °C. High-resolution transmission electron microscopy (HRTEM) is used to characterize the films, showing a monocrystalline structure and confirming epitaxial growth on the 3C-SiC layer. A film ranging in thickness from 3.4 to 4.1 nm shows a superconducting transition temperature of 11.8 K, which is the highest reported for NbN films of comparable thickness. The NbN nano-films on 3C-SiC offer a promising alternative to improve terahertz detectors. For comparison, NbN nanofilms grown directly on Si substrates are also studied by HRTEM.
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74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth

Transverse rectification in superconducting thin films with arrays of asymmetric defects

E. M. Gonzalez, N. O. Nunez, J. V. Anguita, and J. L. Vicent

Appl. Phys. Lett. 91, 062505 (2007); http://dx.doi.org/10.1063/1.2767199 (3 pages) | Cited 14 times

Online Publication Date: 7 August 2007

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Superconducting Nb films have been grown on top of arrays of Cu nanotriangles. These asymmetric pinning centers strongly modify the vortex lattice dynamics. Two rectification effects have been observed: (i) longitudinal ratchet effect when the input currents are injected perpendicular to the triangle reflection symmetry axis and (ii) transverse rectification effect when the input currents are injected parallel to the triangle reflection symmetry axis and the output voltage drop occurs perpendicular to the triangle reflection symmetry axis. Increasing the applied magnetic field, the former shows a change of the output voltage polarity, the transverse output voltage does not show any polarity reversal.
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74.25.F- Transport properties
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.-w Superconducting films and low-dimensional structures

Interface effects at a half-metal/ferroelectric junction

Kunihiko Yamauchi, Biplab Sanyal, and Silvia Picozzi

Appl. Phys. Lett. 91, 062506 (2007); http://dx.doi.org/10.1063/1.2767776 (3 pages) | Cited 23 times

Online Publication Date: 7 August 2007

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Magnetoelectric effects are investigated ab initio at the interface between half-metallic and ferroelectric prototypes: Heusler Co2MnSi and perovskite BaTiO3. For the Co-termination ferroelectricity develops in BaTiO3 down to nanometer thicknesses, whereas for the MnSi termination a paraelectric and a ferroelectric state energetically compete, calling for a full experimental control over the junction atomic configuration whenever a ferroelectric barrier is needed. Switch of the electric polarization largely affects magnetism in Co2MnSi, with magnetoelectric coupling due to electronic hybridization at the MnSi termination and to the structural effects at the Co-termination. Half metallicity is lost at the interface, but recovered already in the subsurface layer.
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77.80.Fm Switching phenomena
75.80.+q Magnetomechanical effects, magnetostriction
77.22.Ej Polarization and depolarization
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Cc Other ferromagnetic metals and alloys

Spin-torque ferromagnetic resonance measurements of damping in nanomagnets

G. D. Fuchs, J. C. Sankey, V. S. Pribiag, L. Qian, P. M. Braganca, A. G. F. Garcia, E. M. Ryan, Zhi-Pan Li, O. Ozatay, D. C. Ralph, and R. A. Buhrman

Appl. Phys. Lett. 91, 062507 (2007); http://dx.doi.org/10.1063/1.2768000 (3 pages) | Cited 35 times

Online Publication Date: 7 August 2007

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The authors directly measure the magnetic damping parameter α in thin-film CoFeB and Permalloy (Py) nanomagnets at room temperature using a recently developed ferromagnetic resonance technique where the precessional mode of an individual nanomagnet can be excited by microwave-frequency spin-transfer torque and detected by the giant magnetoresistance effect. The authors obtain αCoFeB = 0.014±0.003 and αPy = 0.010±0.002, values comparable to measurements for extended thin films, establishing that patterned nanomagnets can exhibit magnetic damping that is consistent with that of unpatterned bulk material.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
75.30.Ds Spin waves
75.47.De Giant magnetoresistance
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Magnetocaloric effect in MnSi

Parul Arora, M. K. Chattopadhyay, and S. B. Roy

Appl. Phys. Lett. 91, 062508 (2007); http://dx.doi.org/10.1063/1.2768005 (3 pages) | Cited 5 times

Online Publication Date: 7 August 2007

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The temperature dependence of heat capacity of MnSi has been measured in the presence of different values of magnetic field. When the magnetic field is applied, an appreciable adiabatic temperature change is observed in the compound. The entropy change due to isothermal change of magnetic field is found to be significant well above the ordering temperature of the compound. This produces a large refrigerant capacity in MnSi, making it important for applications in refrigeration cycles.
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75.30.Sg Magnetocaloric effect, magnetic cooling
65.40.G- Other thermodynamical quantities
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

Controllable nanocrystallization in amorphous Nd9Fe85B6 via combined application of severe plastic deformation and thermal annealing

Wei Li, Lanlan Li, Yun Nan, Xiaohong Li, Xiangyi Zhang, D. V. Gunderov, V. V. Stolyarov, and A. G. Popov

Appl. Phys. Lett. 91, 062509 (2007); http://dx.doi.org/10.1063/1.2768023 (3 pages) | Cited 15 times

Online Publication Date: 7 August 2007

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The control of nanocrystal formation in amorphous alloys is of particular importance for the development of advanced nanocrystalline materials. In the present study, the authors succeeded in controlling α-Fe and Nd2Fe14B nanocrystallization processes in amorphous Nd9Fe85B6 by a combination of severe plastic deformation at room temperature and subsequent thermal annealing. The α-Fe/Nd2Fe14B nanocomposite magnets prepared by this approach possess homogeneously distributed nanocrystals with a small size, 15 nm for α-Fe phase and 26 nm for Nd2Fe14B, and therefore show enhanced magnetic properties as compared to those prepared by directly annealing amorphous Nd9Fe85B6.
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81.16.-c Methods of micro- and nanofabrication and processing
81.40.Gh Other heat and thermomechanical treatments
81.40.Lm Deformation, plasticity, and creep
75.50.Ww Permanent magnets
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials

Ferromagnetism in nanoscale BiFeO3

R. Mazumder, P. Sujatha Devi, Dipten Bhattacharya, P. Choudhury, A. Sen, and M. Raja

Appl. Phys. Lett. 91, 062510 (2007); http://dx.doi.org/10.1063/1.2768201 (3 pages) | Cited 91 times

Online Publication Date: 7 August 2007

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A remarkably high saturation magnetization of ∼ 0.4μB/Fe along with room temperature ferromagnetic hysteresis loop has been observed in nanoscale (4–40 nm) multiferroic BiFeO3 which in bulk form exhibits weak magnetization ( ∼ 0.02μB/Fe) and an antiferromagnetic order. The magnetic hysteresis loops exhibit exchange bias and vertical asymmetry which could be because of spin pinning at the boundaries between ferromagnetic and antiferromagnetic domains. Interestingly, both the calorimetric and dielectric permittivity data in nanoscale BiFeO3 exhibit characteristic features at the magnetic transition point. These features establish the formation of a true ferromagnetic-ferroelectric system with a coupling between the respective order parameters in nanoscale BiFeO3.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Tuned permeability in terahertz split-ring resonators for devices and sensors

T. Driscoll, G. O. Andreev, D. N. Basov, S. Palit, S. Y. Cho, N. M. Jokerst, and D. R. Smith

Appl. Phys. Lett. 91, 062511 (2007); http://dx.doi.org/10.1063/1.2768300 (3 pages) | Cited 49 times

Online Publication Date: 7 August 2007

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A process is demonstrated for tuning the magnetic resonance frequency of a fixed split-ring resonator array, by way of adding material near the split-ring elements. Applying drops of a silicon-nanospheres/ethanol solution to the surface of the sample decreases the magnetic resonance frequency of the split-ring array in incremental steps of 0.03 THz. This fine tuning is done post fabrication and is demonstrated to be reversible. The exhibited sensitivity of the split-ring resonance frequency to the presence of silicon nanospheres also suggests further application possibilities as a sensor device.
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07.55.-w Magnetic instruments and components
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
84.40.-x Radiowave and microwave (including millimeter wave) technology

Current-induced magnetization switching in asymmetric necked wires

S. Lepadatu, J. Wu, and Y. B. Xu

Appl. Phys. Lett. 91, 062512 (2007); http://dx.doi.org/10.1063/1.2768301 (3 pages) | Cited 3 times

Online Publication Date: 7 August 2007

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The authors have studied the current-induced domain wall movement mechanism in Ni80Fe20 wires patterned with a nanoconstriction and asymmetric arm widths using transport and focused magneto-optic Kerr effect (MOKE) measurements. Using dc current, the trapped domain wall is removed from the constriction at a current density greater than 1011 A/m2 and the direction of domain wall displacement is detected using focused MOKE measurements. At zero field, the current-induced domain wall displacement is in the direction of the current carriers while at the nucleation field of the domain wall the displacement direction is set by the direction of the applied field, independent of the current direction.
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75.60.Ch Domain walls and domain structure
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
78.20.Ls Magneto-optical effects

Effect of ferromagnetic nanoparticles on the transport properties of a GaMnAs microbridge

M. V. Sapozhnikov, A. A. Fraerman, S. N. Vdovichev, B. A. Gribkov, S. A. Gusev, A. Yu. Klimov, V. V. Rogov, Joonyeon Chang, Hyungjun Kim, Hyun Cheol Koo, Suk-Hee Han, and S. H. Chun

Appl. Phys. Lett. 91, 062513 (2007); http://dx.doi.org/10.1063/1.2768304 (3 pages) | Cited 1 time

Online Publication Date: 7 August 2007

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A chain of Co nanoparticles was formed along a GaMnAs microbridge by electron beam lithography. The magnetic state of the particles was manipulated by a magnetic force microscope probe. It was found that resistance of the microbridge depended on the state of the particles and was different for the particles in the single-domain and vortex states. The resistance exhibited steplike behavior in an external magnetic field. This behavior was the result of the effect of the inhomogeneous stray fields of the particles on the microbridge resistance. The observed phenomenon can be used as an alternative way to control GaMnAs transport properties.
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73.63.-b Electronic transport in nanoscale materials and structures
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
75.50.Pp Magnetic semiconductors
75.60.Ch Domain walls and domain structure

Unusual resistivity hysteresis in a bulk magnetoresistive ferromagnetic/ferrimagnetic composite (La0.7Ca0.3MnO3/Mn3O4): Role of demagnetization effects

B. Vertruyen, R. Cloots, M. Ausloos, J.-F. Fagnard, and Ph. Vanderbemden

Appl. Phys. Lett. 91, 062514 (2007); http://dx.doi.org/10.1063/1.2768883 (3 pages) | Cited 5 times

Online Publication Date: 8 August 2007

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The authors report an intriguing resistivity versus magnetic field dependence in polycrystalline composite samples containing a magnetoresistive manganite (ferromagnetic/conducting La0.7Ca0.3MnO3) and a magnetic manganese oxide (ferrimagnetic/insulating Mn3O4). At 10 K, when the magnetic field is scanned from positive to negative values, the resistance peak occurs at positive magnetic field, instead of zero or negative field as usually observed in polycrystalline manganite samples. The position of the resistance peak agrees well with the cancellation of the internal magnetic field, suggesting that the demagnetization effects are responsible for this behavior.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Gg Ferrimagnetics
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Asymmetric magnetization reversal behavior in exchange-biased NiFe/MnPt bilayers in two different anisotropy regimes: Close and far from critical thickness

D. Spenato, V. Castel, S. P. Pogossian, D. T. Dekadjevi, and J. Ben Youssef

Appl. Phys. Lett. 91, 062515 (2007); http://dx.doi.org/10.1063/1.2768896 (3 pages) | Cited 12 times

Online Publication Date: 9 August 2007

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The effect of the ratio between the uniaxial and unidirectional anisotropy on magnetization reversal in NiFe/MnPt bilayers has been systematically studied using vectorial vibrating magnetometer. Depending on the balance between these two anisotropies the magnetization reverses either in the opposite or the same semicircles during the ascending and descending branches of the hysteresis loop. A simple modified coherent rotation model provides a good description of the magnetization reversal in these bilayers.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.60.Jk Magnetization reversal mechanisms

Spatially resolved electron energy-loss spectroscopy of electron-beam grown and sputtered CoFeB/MgO/CoFeB magnetic tunnel junctions

Judy J. Cha, J. C. Read, R. A. Buhrman, and David A. Muller

Appl. Phys. Lett. 91, 062516 (2007); http://dx.doi.org/10.1063/1.2769753 (3 pages) | Cited 24 times

Online Publication Date: 10 August 2007

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Electron energy-loss spectroscopy at subnanometer resolution is used to investigate CoFeB/MgO/CoFeB magnetic tunnel junctions grown by electron-beam evaporation and radio frequency (rf) sputtering before and after annealing. Gap states were observed in the MgO layer for both growth methods although the rf-sputtered MgO layer showed significantly more gap states. Asymmetry in oxygen bonding between the top and bottom CoFeB/MgO interfaces was also observed. Moreover, significant amounts of diffused B as BOx were observed in the rf-sputtered MgO layer. A Mg underlayer between the MgO layer and the bottom electrode greatly reduced BOx formation in the barrier upon annealing.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
79.20.-m Impact phenomena (including electron spectra and sputtering)
79.20.Uv Electron energy loss spectroscopy
81.15.Cd Deposition by sputtering
81.40.Gh Other heat and thermomechanical treatments

Magnetic properties of nanocrystalline Fe82.65Cu1.35SixB16−x alloys (x = 0–7)

Motoki Ohta and Yoshihito Yoshizawa

Appl. Phys. Lett. 91, 062517 (2007); http://dx.doi.org/10.1063/1.2769956 (3 pages) | Cited 20 times

Online Publication Date: 10 August 2007

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The Si content dependences of the magnetic properties of the Fe82.65Cu1.35SixB16−x alloys prepared by melt spinning were studied. The maximum Bs and minimum Hc were observed at around x = 2 for the annealed Fe82.65Cu1.35SixB16−x alloys. The Bs and Hc of the annealed Fe82.65Cu1.35Si2B14 alloy were 1.84 T and 6.5 A/m, respectively. The average grain size of the bcc Fe nanocrystal in the annealed alloys with x ⩽ 2 was about 20 nm, it increased with x at x>2. The annealing temperature range without the precipitation of o-Fe3B expanded with Si content.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.Hk Nanocrystals
81.40.Gh Other heat and thermomechanical treatments
81.30.Mh Solid-phase precipitation
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