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1 Apr 2012

Volume 111, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 071101 (2012); http://dx.doi.org/10.1063/1.3694674 (23 pages)

Shunfeng Li and Andreas Waag
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back to top New Magnetic Materials, Instrumentation, and Measurement Techniques

Structural, magnetic, and electron transport properties of MnBi:Fe thin films

P. Kharel, X. Z. Li, V. R. Shah, N. Al-Aqtash, K. Tarawneh, R. F. Sabirianov, R. Skomski, and D. J. Sellmyer

J. Appl. Phys. 111, 07E326 (2012); http://dx.doi.org/10.1063/1.3675615 (3 pages) | Cited 2 times

Online Publication Date: 1 March 2012

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The structural, magnetic, and electron transport properties of Mn55−xFexBi45 (x = 0, 2, 4, 5, 8, 11, 13, 16) films prepared by multilayer deposition and annealing using e-beam evaporation have been investigated. Fe doping has produced a significant change in the magnetic properties of the samples including the decrease in saturation magnetization and magnetocrystalline anisotropy and increase in coercivity. Although the magnetization shows a smooth decrease with increasing Fe concentration, the coercivity jumps abruptly from 8.5 kOe to 22 kOe as Fe content changes from 4% to 5%, but the change in coercivity is small as the concentration goes beyond 5%. The temperature dependence of resistivity shows that the samples with low Fe concentration (≤4%) are metallic, but the resistivity increases unexpectedly as the concentration reaches 5%, where the resistance increases with decreasing temperature below 300 K. First-principle calculations suggest that the observed magnetic properties can be understood as the consequences of competing ferromagnetic and antiferromagnetic exchange interactions between the interstitial atom and the rest of the MnBi lattice.
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75.70.Ak Magnetic properties of monolayers and thin films
81.05.Bx Metals, semimetals, and alloys
68.55.A- Nucleation and growth
81.15.Dj E-beam and hot filament evaporation deposition
73.61.At Metal and metallic alloys
75.30.Gw Magnetic anisotropy

Structural and electrical properties of half-Heusler La-Pt-Bi thin films grown by 3-source magnetron co-sputtering

Tetsuya Miyawaki, Nozomi Sugimoto, Naoto Fukatani, Tatsuhiko Yoshihara, Kenji Ueda, Nobuo Tanaka, and Hidefumi Asano

J. Appl. Phys. 111, 07E327 (2012); http://dx.doi.org/10.1063/1.3675986 (3 pages) | Cited 3 times

Online Publication Date: 1 March 2012

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Half-Heusler La-Pt-Bi thin films have been deposited on YAlO3(001) substrate by 3-source magnetron co-sputtering. Control of the Bi content was the critical factor to obtain single phase, c-axis-oriented thin films. Generation of secondary phases was effectively prevented by precise control of the deposition rate for separate targets as well as adjustment of the deposition temperature. The realization of single-phase LaPtBi thin films will provide new potential applications to topological insulating devices based on Heusler alloys.
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73.61.At Metal and metallic alloys
81.15.Cd Deposition by sputtering
68.55.at Other materials

Single-core fluxgate gradiometer with simultaneous gradient and homogeneous feedback operation

Michal Janosek, Pavel Ripka, Frank Ludwig, and Meinhard Schilling

J. Appl. Phys. 111, 07E328 (2012); http://dx.doi.org/10.1063/1.3676238 (3 pages)

Online Publication Date: 6 March 2012

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A novel configuration of a single-core gradiometer, utilizing both homogeneous and gradient feedback operation, is presented. The fluxgate gradiometer comprises of a standard pick-up/ feedback coil and an additional gradient pickup/feedback coil with two separate electronic blocks. The 40-mm-long gradient coil is concentric and coaxial with the homogeneous pickup/feedback coil: the gradient coil assembly was slipped over an already existing race-track fluxgate sensor. The gradient coil works as a pick-up coil and it also generates the compensating field which well approximates a first-order gradient field with zero spatial-mean value. Together with the compensating field from the homogeneous feedback coil, it is thus always possible to measure in two independent feedback loops the homogeneous and gradient field components. The 1/f gradient noise is 4 nT/m/√Hz @ 1 Hz, and it can be further improved by separating the gradient feedback and compensating coil.
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07.55.Ge Magnetometers for magnetic field measurements
84.32.Hh Inductors and coils; wiring

Loss characterization of Mo-doped FeNi flake for DC-to-DC converter and MHz frequency applications

Yang Zhou, Xiaoming Kou, Mingkai Mu, Brandon M. McLaughlin, Xing Chen, Paul E. Parsons, Hao Zhu, Alex Ji, Fred C. Lee, and John Q. Xiao

J. Appl. Phys. 111, 07E329 (2012); http://dx.doi.org/10.1063/1.3677310 (3 pages) | Cited 1 time

Online Publication Date: 7 March 2012

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Magnetic core materials with low loss, high magnetic induction, large permeability, and high working frequencies above 1 MHz are in high demand in the next generation of miniaturized power electronic devices. Magnetic flake based composite materials have been developed to take advantage of high operating frequency ranges, low eddy current losses, high magnetic induction, and low cost fabrication methods. In this study, Mo-doped FeNi flakes with thicknesses of 0.4 ± 0.2 μm to 1.6 ± 0.5 μm have been successfully fabricated with high energy ball milling. The lateral size of the flake is around 100 μm. After being hot-pressed with polymers, all of the samples show initial permeability higher than 40 in the frequency range up to 10 MHz and a loss tangent lower than 0.1. At high excitations, the composite materials show core losses 5 times lower than that of Fe flakes at 800 kHz.
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84.30.Jc Power electronics; power supply circuits
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

Ultra low power processor using perpendicular-STT-MRAM/SRAM based hybrid cache toward next generation normally-off computers

Kumiko Nomura, Keiko Abe, Hiroaki Yoda, and Shinobu Fujita

J. Appl. Phys. 111, 07E330 (2012); http://dx.doi.org/10.1063/1.3677444 (3 pages) | Cited 1 time

Online Publication Date: 7 March 2012

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This paper presents novel processor architecture for HP-processor with MRAM/SRAM-based hybrid cache memory. By simulations of HP-processor using MTJs, it has been clarified that total power of the HP-processor using perpendicular-(p-)STT-MRAM [H. Yoda, et al., Current Appl. Phys. 10, e87 (2010)] can be reduced by 50.2% without any degradation of operation speed. This is the first report on effectively decreasing total power of HP-processors with no degradation of performance using magnetic memory. The presented architecture will be the first step to realize the next generation “normally-off computers.”
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84.30.Sk Pulse and digital circuits
85.75.Bb Magnetic memory using giant magnetoresistance

Magneto-optical Kerr effect measurements on highly ordered nanomagnet arrays

Sachin Pathak and Manish Sharma

J. Appl. Phys. 111, 07E331 (2012); http://dx.doi.org/10.1063/1.3677647 (3 pages) | Cited 1 time

Online Publication Date: 7 March 2012

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In magnetic nanostructures, anisotropy directly influences formation of domains and their evolution with external field. Magneto-optic Kerr effect (MOKE) was used to study samples fabricated by templated electrodeposition of Cobalt into anodic aluminum oxide (AAO) templates. With proper conditions, both Co solid nanowire, as well as hollow nanotubule arrays, were formed. The morphology of the samples was investigated using SEM and AFM. Since as-deposited samples have high surface roughness, chemical mechanical polishing was used to polish the samples to achieve an optically flat surface. MOKE data show that shape anisotropy dominates along the long dimension and interaction effects between nanowires are important. A marked difference is seen between solid nanowires and hollow nanotubule samples, the latter showing formation of vortices.
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75.75.-c Magnetic properties of nanostructures
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms

A study of the perpendicular magnetic microstructure of the L10 FePt epitaxial film using electron holography

J. K. Park, W. H. Lee, J. H. Yoo, and J. M. Yang

J. Appl. Phys. 111, 07E332 (2012); http://dx.doi.org/10.1063/1.3677649 (3 pages)

Online Publication Date: 7 March 2012

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The magnetic microstructure of the L10 FePt perpendicular magnetic film, grown epitaxially on MgO substrate, was studied using high-resolution electron holography. It was shown that the hologram-fringe information of stray-fields can be used to determine the sense of stray-fields and thus, the sense of perpendicular magnetizations inside the film. Furthermore, we were able to directly reveal the detailed perpendicular magnetic structure of L10 FePt epitaxial film by constructing unwrapped phase-image and induction mapping. The perpendicular induction-strength was varying with the domain size. The variation of induction-strength was due to a variation of the degree of ordering in the weakly ordered film.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
42.40.My Applications
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic and magnetocaloric properties of the new rare-earth–transition-metal intermetallic compound Gd3Co29Ge4B10

P. Hill, Igor Dubenko, Tapas Samanta, Abdiel Quetz, and Naushad Ali

J. Appl. Phys. 111, 07E333 (2012); http://dx.doi.org/10.1063/1.3677658 (3 pages) | Cited 1 time

Online Publication Date: 7 March 2012

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The compounds Gd3-xYxCo29Ge4B10 (x = 0, 0.5, 1.0, 1.5, and 3.0), Gd3Co29Al4B10, and Gd3Co29Al4B10 were synthesized by arc melting, and their magnetic properties investigated as a function of temperature and applied magnetic field. X-ray measurements showed primarily single-phase samples with the tetragonal crystal structure P4/nmm. It was found that Gd3Co29Ge4B10 orders ferromagnetically at TC = 212 K and shows a compensation point at 128 K, indicating a ferrimagnetic ordering of the Co and Gd moments. An entropy change of −ΔS = 0.5 J/kgK was observed in a 5-T field at TC for this sample, while a change in sign for this quantity was observed both at the maximum value of magnetization (around 200 K) and then again at the compensation point. Substitution of Y for Gd in Gd3Co29Ge4B10 does not affect the Curie temperature, but shifts the compensation point to lower temperatures. This indicates that a decrease in Gd concentration does not affect the d-d exchange interaction, but has a pronounced effect on the f-d exchange interaction.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Cc Other ferromagnetic metals and alloys
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Dk Alloys
75.30.Cr Saturation moments and magnetic susceptibilities

Structural properties and magnetic phase transition in HoNi2Mn (57Fe)

J. L. Wang, S. J. Campbell, M. Hofmann, M. Hoelzel, R. Zeng, S. X. Dou, and S. J. Kennedy

J. Appl. Phys. 111, 07E334 (2012); http://dx.doi.org/10.1063/1.3677666 (3 pages) | Cited 1 time

Online Publication Date: 7 March 2012

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The structural and magnetic properties of HoNi2Mn(57Fe) have been investigated. The 57Fe-doped HoNi2Mn compound crystallizes in the MgCu2-type structure with Fd-3m space group similar to HoNi2 and HoMn2. HoNi2Mn(57Fe) exhibits ferrimagnetic ordering below a Curie temperature of TC ∼ 60 K—significantly higher than the corresponding values for HoNi2 (TC = 15 K) and HoMn2 (TC = 24 K)—with analyses of dc magnetization and ac susceptibility results confirming that the magnetic transition at TC is second order. The Mössbauer spectra above TC are described well by two sub-spectra representing the 8a and 16d sites while below TC the spectra have been fitted using a site model comprising three sub-spectra. The Debye temperature, θD = 190(20) K, has been determined.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.80.+y Mössbauer effect; other γ-ray spectroscopy
61.66.Dk Alloys

Synthesis, structure, and magnetic properties of M(N3)2(bpy)

Dušan Danilović, Youcef Hamida, C. L. Lin, Tan Yuen, Kunhao Li, and Jing Li

J. Appl. Phys. 111, 07E335 (2012); http://dx.doi.org/10.1063/1.3677774 (3 pages) | Cited 1 time

Online Publication Date: 8 March 2012

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Powder crystalline metal-organic frameworks (MOF), M(N3)2(bpy) (where M = Ni, Co, Cu, and bpy = 4,4′-bipyridine), were successfully synthesized by mixing M(II) salts with solutions of 4,4′-bipyridine and NaN3. All three MOFs crystallize in an orthorhombic crystal system with the space group Cmmm (No. 65), which is isostructural to that of 2D-Fe(N3)2(bpy). The M(II) ions are coordinated with four azide ligands (N3) in equatorial plane forming linear magnetic chains. Isothermal magnetization, magnetic susceptibility, and heat capacity measurements were performed. No clear phase transitions were observed. The intra-chain magnetic interaction was found to be ferromagnetic for the Co and Ni compounds, and antiferromagnetic for the Cu compound. The data were fit to theoretical models, and the variation in the exchange interactions was interpreted in terms of the geometric distortions on the octahedral M(II) sites.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Hq Organic compounds
75.30.Cr Saturation moments and magnetic susceptibilities
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics

Design of a 270ps-access 7-transistor/2-magnetic-tunnel-junction cell circuit for a high-speed-search nonvolatile ternary content-addressable memory

Shoun Matsunaga, Akira Katsumata, Masanori Natsui, Tetsuo Endoh, Hideo Ohno, and Takahiro Hanyu

J. Appl. Phys. 111, 07E336 (2012); http://dx.doi.org/10.1063/1.3677875 (3 pages) | Cited 1 time

Online Publication Date: 8 March 2012

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A novel 7-transistor/2-magnetic-tunnel-junction (7 T-2MTJ) cell circuit is proposed for a high-speed and compact nonvolatile ternary content-addressable memory (TCAM). Since critical path for switching in the TCAM cell circuit, which determines the performance of the TCAM, is only a single MOS transistor, switching delay of the TCAM word circuit is minimized. As a result, 270 ps of switching delay in 144-bit TCAM word circuit is achieved under a 90 nm CMOS/MTJ technology with magneto-resistance ratio of 100%, which is about two times faster than a conventional CMOS-based TCAM.
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85.75.Dd Magnetic memory using magnetic tunnel junctions
84.30.Sk Pulse and digital circuits
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices

Clocking magnetic field-coupled devices by domain walls

György Csaba, Josef Kiermaier, Markus Becherer, Stephan Breitkreutz, Xueming Ju, Paolo Lugli, Doris Schmitt-Landsiedel, and Wolfgang Porod

J. Appl. Phys. 111, 07E337 (2012); http://dx.doi.org/10.1063/1.3677879 (3 pages)

Online Publication Date: 8 March 2012

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We study the interaction between propagating domain walls in permalloy nanowires and nanomagnetic dots made of Co/Pt multilayers. The magnetic behavior of dots placed above/below the domain wall conductor is strongly influenced by the field of the wall. Using micromagnetic simulations we show that the field generated by the domain wall can switch the coupled dots to their magnetically ordered ground state. This effect can be exploited for clocking magnetic field-coupled devices and possibly substitute electrical clocking structures.
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75.30.-m Intrinsic properties of magnetically ordered materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.-d Domain effects, magnetization curves, and hysteresis
75.75.Fk Domain structures in nanoparticles
75.78.Cd Micromagnetic simulations
73.21.Ac Multilayers

Atomic structure and magnetic properties of Fe1–xCox alloys

Manh Cuong Nguyen, Xin Zhao, Min Ji, Cai-Zhuang Wang, Bruce Harmon, and Kai-Ming Ho

J. Appl. Phys. 111, 07E338 (2012); http://dx.doi.org/10.1063/1.3677929 (3 pages)

Online Publication Date: 9 March 2012

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Using genetic algorithm with first-principle calculations, we searched for low-energy crystal structures of Fe1−xCox alloys. We found that Fe1−xCox alloys are highly configurationally degenerate with many additional off-stoichiometric stable structures to the well-known B2 structure. The average magnetic moment of Fe atom increases with concentration of Co in the alloy, while that of Co atom is almost constant, which are consistent with experiments and earlier studies. The magnetic moment of Fe atom is strongly dependent on the number of Co nearest neighbor and it increases with this number.
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75.30.Cr Saturation moments and magnetic susceptibilities
61.66.Bi Elemental solids
61.66.Dk Alloys
71.15.-m Methods of electronic structure calculations
71.20.Be Transition metals and alloys

Influence of magnetic material composition of Fe100−xBx coated tip on the spatial resolution of magnetic force microscopy

Mitsuru Ohtake (大竹充), Kazuki Soneta (椊田和希), and Masaaki Futamoto (二本正昭)

J. Appl. Phys. 111, 07E339 (2012); http://dx.doi.org/10.1063/1.3678298 (3 pages) | Cited 2 times

Online Publication Date: 9 March 2012

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Magnetic force microscope (MFM) tips are prepared by coating Si tips of 3 nm radius with 20-nm-thick Fe100−xBx (x = 0, 8, 18, and 34 at. %) alloys. As the B composition increases, the wettability of Fe-B alloy material to Si surface increases and a sharper and smoother MFM tip is obtained. The remanent magnetization of Fe-B alloy material decreases with increasing the B composition, which degrades the MFM signal detection sensitivity. The MFM resolution is influenced by both the tip sharpness and the remanent magnetization of coated Fe-B alloy material. Resolutions of 10.2, 9.2, 7.3, and 9.3 nm are obtained with tips coated with Fe, Fe92B8, Fe82B18, and Fe66B34 materials, respectively. Magnetic bits of 14.9 nm in length of a perpendicular magnetic medium recorded at 1700 kfci are distinguishable in the MFM image observed by using an Fe82B18-alloy coated tip. Fe-B coated tips are suitable to observe the magnetization structures of future high-density recording media. © 2012 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.65.-b Surface treatments
75.50.Tt Fine-particle systems; nanocrystalline materials

Magnetostriction measurement of a giant magnetoresistance film on a practical substrate covered by a shield layer

Kazuhiko Okita, Kazushi Ishiyama, and Hideo Miura

J. Appl. Phys. 111, 07E340 (2012); http://dx.doi.org/10.1063/1.3678445 (3 pages) | Cited 1 time

Online Publication Date: 9 March 2012

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Magnetostriction constant of a magnetic thin film is conventionally measured by detecting the deformation of a coupon sample that consists of the magnetic film deposited on a thin glass substrate (e.g., cover glass of size 10 mm × 25 mm) under an applied field using a laser beam [A. C. Tam and H. Schroeder, J. Appl. Phys. 64, 5422 (1988)]. This method, however, cannot be applied to films deposited on actual large-size substrates (wafers) with diameter from 3 to 6 in. or more. In a previous paper [Okita et al., J. Phys.: Conf. Ser. 200, 112008 (2010)], the authors presented a method for measuring magnetostriction of a magnetic thin film deposited on an actual substrate by detecting the change of magnetic anisotropy field, Hk, under mechanical bending of the substrate. It was validated that the method is very effective for measuring the magnetostriction constant of a free layer on the actual substrate. However, since a Ni-Fe shield layer usually covers a magnetic head used for a hard disk drive, this shield layer disturbs the effective measurement of R-H curve under minor loop. Therefore, a high magnetic field that can saturate the magnetic material in the shield layer should be applied to the head in order to measure the magnetostriction constant of a pinned layer under the shield layer. In this paper, this method was applied to the measurement of the magnetostriction constant of a pinned layer under the shield layer by using a high magnetic field up to 320 kA/m (4 kOe).
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75.80.+q Magnetomechanical effects, magnetostriction
81.40.Lm Deformation, plasticity, and creep
68.55.aj Insulators
75.30.Gw Magnetic anisotropy
75.47.De Giant magnetoresistance
75.70.Ak Magnetic properties of monolayers and thin films

Electrical input structures for nanomagnetic logic devices

J. Kiermaier, S. Breitkreutz, G. Csaba, D. Schmitt-Landsiedel, and M. Becherer

J. Appl. Phys. 111, 07E341 (2012); http://dx.doi.org/10.1063/1.3678584 (3 pages) | Cited 1 time

Online Publication Date: 9 March 2012

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Co/Pt nanomagnets close to a current driven wire are proposed as an electrical input interface for nanomagnetic logic. Their switching field shows a significant dependence of the external magnetic field sweep rate and the temperature, which can be modeled by the calibrated Sharrock formula, realizing coercivity extrapolations in the µs time scale. The influence of the current pulse in the wire is modeled as a generated Oersted field and an additional temperature rise in the structure. The models are used to simulate the current pulse characteristics sufficient to control the input magnet. Oersted switching experiments verify the proposed modeling, visualize controlled nanomagnets in close vicinity of the wire and thereby demonstrate the functionality of the input device.
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85.70.-w Magnetic devices
84.30.Sk Pulse and digital circuits

Structural and magnetic properties of planar nanowire arrays of Co grown on oxidized vicinal silicon (111) templates

S. K. Arora, B. J. O’Dowd, C. Nistor, T. Balashov, B. Ballesteros, A. Lodi Rizzini, J. J. Kavich, S. S. Dhesi, P. Gambardella, and I. V. Shvets

J. Appl. Phys. 111, 07E342 (2012); http://dx.doi.org/10.1063/1.3679033 (3 pages)

Online Publication Date: 9 March 2012

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We fabricated planar arrays of Co nanowires (NWs) on oxidized step-bunched Si (111) templates using shallow angle deposition. These planar NW arrays exhibit ferromagnetic behavior at room temperature for NW widths down to 25 nm. The NWs possess polycrystalline character with hcp-crystal structure, and present a lightly oxidized interface when capped with MgO. The magnetic anisotropy of the NW array is dominated by the shape anisotropy, which keeps the magnetization in-plane with easy axis parallel to the wires. By reducing the inter-wire separation, we obtain NW arrays with reduced coercivity demonstrating the importance of magneto-static interactions in determining the magnetic properties of the NWs.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.Cd Fabrication of magnetic nanostructures
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Restoration the domain structure from magnetic force microscopy image

Dongping Wu, Yuanfu Lou, Fulin Wei, and Dan Wei

J. Appl. Phys. 111, 07E343 (2012); http://dx.doi.org/10.1063/1.3679389 (3 pages)

Online Publication Date: 12 March 2012

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This contribution gives an approximation method to calculate the stray field of the scanning plane from the magnetic force microscopy (MFM) force gradient image. Before calculation, a Butterworth low-pass filter has been used to remove a part of the noise of the image. The discrete Fourier transform (DFT) method has been used to calculate the magnetic potential of the film surface. It shows that the potential is not correct because the low-frequency noise has been enlarged. The approximation method gives a better result of the potential and proves that the MFM force gradient of the perpendicular component image also gives the perpendicular component of the stray field. Supposing that the distance between the tip and the sample is as small as near zero, the force gradient image also gives the magnetic charge distribution of the film surface. So if the orientation of the film from hysteresis loop is known, then the domain structure of the film can be determined. For perpendicular orientation, the absolution value of the perpendicular component of stray field gives the domain and domain wall position. For in-plane orientation, the absolution value of in-plane component of stray field gives the domain and domain wall position.
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75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
68.37.Rt Magnetic force microscopy (MFM)

A model-assisted technique for characterization of in-plane magnetic anisotropy

B. Fan and C. C. H. Lo

J. Appl. Phys. 111, 07E344 (2012); http://dx.doi.org/10.1063/1.3679435 (3 pages)

Online Publication Date: 12 March 2012

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This paper describes a novel technique for characterizing in-plane magnetic anisotropy, such as stress anisotropy. The method involves applying a radially spreading ac field to a test sample, and detects simultaneously the field signals emanating from the sample surface along different directions using an angular array of Hall effect sensors. The technique was applied to detect the stress-induced anisotropy in an annealed Fe plate. Under uniaxial tension, the field signal measured along the stress axis increases while that along the transverse axis decreases. The stress sensitivity of the technique was characterized in terms of the ratio of the field signals measured along and perpendicular to the stress axis. The ratios measured at both the first- and third-order harmonic frequencies increase monotonically with stress, with the latter showing a higher stress sensitivity. The stress dependence of the field signal ratio was modeled based on the magnetomechanical effect theory, and was found to agree with the experimental results.
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75.30.Gw Magnetic anisotropy
75.80.+q Magnetomechanical effects, magnetostriction
81.40.Gh Other heat and thermomechanical treatments

Ultrahard magnetic nanostructures

P. K. Sahota, Y. Liu, R. Skomski, P. Manchanda, R. Zhang, M. Franchin, H. Fangohr, G. C. Hadjipanayis, A. Kashyap, and D. J. Sellmyer

J. Appl. Phys. 111, 07E345 (2012); http://dx.doi.org/10.1063/1.3679453 (3 pages) | Cited 2 times

Online Publication Date: 13 March 2012

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The performance of hard-magnetic nanostructures is investigated by analyzing the size and geometry dependence of thin-film hysteresis loops. Compared to bulk magnets, weight and volume are much less important, but we find that the energy product remains the main figure of merit down to very small features sizes. However, hysteresis loops are much easier to control on small length scales, as epitomized by Fe-Co-Pt thin films with magnetizations of up to 1.78 T and coercivities of up to 2.52 T. Our numerical and analytical calculations show that the feature size and geometry have a big effect on the hysteresis loop. Layered soft regions, especially if they have a free surface, are more harmful to coercivity and energy product than spherical inclusions. In hard-soft nanocomposites, an additional complication is provided by the physical properties of the hard phases. For a given soft phase, the performance of a hard-soft composite is determined by the parameter (Ms - Mh)/Kh.
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75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Vv High coercivity materials
75.50.Ww Permanent magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Characteristics of magnetic force microscopy magnetics on high moment perpendicular magnetic recording writers with high coercivity probes

Feng Liu, Shaoping Li, Daniel Bai, James Wang, Zhanjie Li, Dehua Han, Tao Pan, and Sining Mao

J. Appl. Phys. 111, 07E346 (2012); http://dx.doi.org/10.1063/1.3679557 (3 pages)

Online Publication Date: 13 March 2012

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High resolution magnetic force microscopy (MFM) imaging with high coercivity probes on perpendicular magnetic recording (PMR) writers directly characterizes magnetic field contour for the writer main pole as well as its shields’ magnetic state. Evolution of write bubble and return field was analyzed by MFM imaging in dynamic phase detection scheme. Different write field components and their out of plane second order derivatives were calculated via finite element modeling. The MFM imaged write field distribution correlates well with the PMR writer out of plane write field component. Magnetic responses of the PMR writer main pole, trailing and side shields are quantified. The trailing and side shields exhibit complicated magnetic saturation behaviors comparing with the PMR writer pole. The side shield’s magnetic response is dependent upon its initial equilibrium state.
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75.50.Ww Permanent magnets

Analysis of effective permeability behaviors of magnetic hollow fibers filled in composite

Baekil Nam, Jongryoul Kim, and Kim Ki Hyeon

J. Appl. Phys. 111, 07E347 (2012); http://dx.doi.org/10.1063/1.3679579 (3 pages)

Online Publication Date: 13 March 2012

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In order to predict the permeability behaviors of magnetic hollow fibers and their composites in the high frequency region, we proposed a simple hollow approximation method for hollow shaped magnetic particles using the modified demagnetizing factors of Sato’s and Aharoni’s cylindrical approximation methods. The obtained demagnetizing factors of the hollow magnetic particle by the proposed simple hollow approximation were not distinguished from those of the Beleggia’s complicated analytical results. The effective permeability of the magnetic hollow fiber filled in composite was evaluated using the effective medium theory and self-consistent iteration method using the simple hollow approximation. As the hollow ratio increased, the resonance frequency of the permeability shifted to a higher frequency region for the hollow fiber composite as well as for the single hollow fiber. The results of the calculated permeability using the proposed simple hollow approximation were in good agreement with Beleggia’s complicated analytical results.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials

Effect of packing fraction on ferromagnetic resonance in NiFe2O4 nanocomposites

Han Song, Sam Mulley, Nathan Coussens, Pallavi Dhagat, Albrecht Jander, and Alexandre Yokochi

J. Appl. Phys. 111, 07E348 (2012); http://dx.doi.org/10.1063/1.3679635 (3 pages) | Cited 1 time

Online Publication Date: 13 March 2012

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Magnetic nanocomposites, composed of magnetic nanoparticles in an insulating matrix, can have properties not achievable in bulk, single-phase materials. This work reports on ferromagnetic resonance (FMR) measurements as a tool to investigate the internal magnetic field in nanocomposite samples of varying particle packing fractions. The ferromagnetic resonance frequency changes with particle packing fraction due to increased inter-particle interaction and demagnetizing field within the sample. Experimental results obtained on NiFe2O4 nanocomposite samples are compared to published theoretical models, and found to be consistent with the predicted trends. Extrapolation of the results to the limit of isolated particles indicates an average internal anisotropy field of 0.041 T for the NiFe2O4 nanoparticles.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.75.-c Magnetic properties of nanostructures
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.-d Domain effects, magnetization curves, and hysteresis

Development and validation of a 10 kHz–1 MHz magnetic susceptometer with constant excitation field

Javier Tafur, Adriana P. Herrera, Carlos Rinaldi, and Eduardo J. Juan

J. Appl. Phys. 111, 07E349 (2012); http://dx.doi.org/10.1063/1.3680200 (3 pages)

Online Publication Date: 13 March 2012

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The design and validation of a mutual inductance AC susceptometer with constant excitation field of up to 4.25 Oe, operating at frequencies from 10 kHz to 1 MHz, is presented. Considerations such as parasitic capacitances between wire turns and sensing bridge electronics were taken into account in order to extend the operating frequency range. An 18AWG wire with considerable insulator thickness was used for coil construction to keep parasitic capacitive reactance negligible relative to coil inductive reactance, and to obtain controlled field operation. A high speed instrumentation amplifier (slew rate over 33 V/μs) was designed and constructed using voltage feedback LM7171 operational amplifiers. The system was calibrated with Dy2O3 to account for mismatches in signal amplitude and phase shifts due to the electronics, coil coupling and imperfections, and external disturbances. AC susceptometer operation in the 10 kHz–1 MHz frequency range was validated by measuring the complex susceptibility of cobalt ferrite nanoparticles suspended in solvents of different viscosities. Good agreement was found between the experimental Brownian relaxation times and those predicted theoretically from the viscosity of the suspending media and the hydrodynamic diameter of the nanoparticles.
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07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
84.30.Le Amplifiers
07.68.+m Photography, photographic instruments; xerography

A hybrid magnetic/complementary metal oxide semiconductor process design kit for the design of low-power non-volatile logic circuits

G. Di Pendina, G. Prenat, B. Dieny, and K. Torki

J. Appl. Phys. 111, 07E350 (2012); http://dx.doi.org/10.1063/1.3680013 (3 pages)

Online Publication Date: 21 March 2012

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Since the advent of the MOS transistor, the performance of microelectronic circuits has followed Moore’s law, stating that their speed and density would double every 18 months. Today, this trend tends to get out of breath: the continuously decreasing size of devices and increasing operation frequency result in power consumption and heating issues. Among the solutions investigated to circumvent these limitations, the use of non-volatile devices appears particularly promising. It allows easing, for example, the power gating technique, which consists in cutting-off the power supply of inactive blocks without losing information, drastically reducing the standby power consumption. In this approach, the advantages of magnetic tunnel junctions (MTJs) compared with other non-volatile devices allow one to design hybrid CMOS/magnetic circuits with high performance and new functionalities. Designing such circuits requires integrating MTJs in standard microelectronics design suites. This is performed by means of a process design kit (PDK) for the hybrid CMOS/magnetic technology. We present here a full magnetic PDK, which contains a compact model of the MTJ for electrical simulation, technology files for layout and physical verifications, and standard cells for the design of complex logic circuits and which is compatible with standard design suites. This PDK allows designers to accurately and comfortably design high-performance hybrid CMOS/magnetic logic circuits in the same way as standard CMOS circuits.
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84.30.Sk Pulse and digital circuits
85.30.De Semiconductor-device characterization, design, and modeling
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