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1 May 2012

Volume 111, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 093103 (2012); http://dx.doi.org/10.1063/1.4709385 (8 pages)

Ani Khachatrian, Joseph S. Melinger, and Syed B. Qadri
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back to top Magnetism and Superconductivity

Magnetization configurations of a tri-layer nanopillar ferromagnet/nonmagnetic spacer/ferromagnet

Oksana V. Sukhostavets, Gloria R. Aranda, and Konstantin Y. Guslienko

J. Appl. Phys. 111, 093901 (2012); http://dx.doi.org/10.1063/1.4706560 (10 pages)

Online Publication Date: 1 May 2012

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The equilibrium magnetization configurations of tri-layer circular nanopillar are calculated within micromagnetic approach. Nanopillar is assumed to be a vertical stack of ferromagnetic/nonmagnetic/ferromagnetic layers. The regions of geometrical parameters of nanopillar (radius and thickness), where the magnetic vortices and single domain states appear in the ground state, are calculated analytically and checked by micromagnetic simulations. The interlayer magnetostatic coupling affects essentially the formation of vortices or single domain states in both ferromagnetic layers. A considerable influence of the thicknesses of the ferromagnetic layers and spacer on the stability of vortex states is found. The results can be applied to interpret experiments on spin torque induced magnetization dynamics in nanopillars and tunnel junctions and also to estimate the nanopillar ground states.
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75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

Effect of Li-doping on the magnetic properties of ZnO with Zn vacancies

Hui-Xia Gao and Jian-Bai Xia

J. Appl. Phys. 111, 093902 (2012); http://dx.doi.org/10.1063/1.4707888 (5 pages) | Cited 2 times

Online Publication Date: 1 May 2012

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Using first-principles calculations, we investigate the electronic and magnetic properties of Zn vacancy in ZnO with and without Li-doping. It is found that the Zn vacancy can induce magnetism but the formation energy of the system is high. We also found that the Li-dopant at either the substitutional sites or the interstitial sites and both at two sites can lower the formation energy of Zn vacancy. The total magnetic moments of the system is increased after Li doping at the substitutional site, while it is decreased after Li doping at the interstitial site. In addition, the extended tails of the wave functions of Zn vacancy make long-ranged spin couplings possible. Li atoms at the substitutional sites further stabilize the long-ranged ferromagnetism induced by Zn vacancies. Thus, it is possible to tune the magnetism of ZnO through defect engineering.
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61.72.uj III-V and II-VI semiconductors
71.20.Nr Semiconductor compounds
75.30.Cr Saturation moments and magnetic susceptibilities
81.05.Dz II-VI semiconductors
61.72.jd Vacancies
61.72.jj Interstitials

Interplay between magnetism and chemical structure at spinel-spinel interfaces

B. B. Nelson-Cheeseman, R. V. Chopdekar, M. F. Toney, E. Arenholz, and Y. Suzuki

J. Appl. Phys. 111, 093903 (2012); http://dx.doi.org/10.1063/1.4707890 (6 pages) | Cited 1 time

Online Publication Date: 1 May 2012

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By utilizing a graded wedge sample geometry in combination with surface sensitive soft x-ray techniques, we explain the enhanced magnetic properties observed at the interface between two dissimilar magnetic spinel oxide thin films in terms of the chemical and magnetic character of the constituent cations. Through x-ray absorption spectroscopy and magnetic circular dichroism studies, we find that the interfacial cations exhibit chemical valences and site-occupancies which differ remarkably from the bulk of either film. This results in enhanced magnetic properties localized to the interface region. While this phenomena likely arises from cation interdiffusion of 1–2 nm near the interface due to the open spinel crystal structure, this dramatic change in the magnetic properties localized to a thin interface region may provide a route to obtaining isolated interfacial properties in other spinel-structured heterostructures.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
66.30.Ny Chemical interdiffusion; diffusion barriers
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Minimum quench power dissipation and current non-uniformity in international thermonuclear experimental reactor type NbTi cable-in-conduit conductor samples under direct current conditions

G. Rolando, E. P. A. van Lanen, and A. Nijhuis

J. Appl. Phys. 111, 093904 (2012); http://dx.doi.org/10.1063/1.4709438 (11 pages)

Online Publication Date: 2 May 2012

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The level of current non-uniformity in NbTi cable-in-conduit conductors (CICCs) sections near the joints in combination with the magnetic field profile needs attention in view of proper joint design. The strand joule power and current distribution at quench under DC conditions of two samples of ITER poloidal field coil conductors, as tested in the SULTAN facility, and of the so called PFCI model coil insert, have been analyzed with the numerical cable model JackPot. The precise trajectories of all individual strands, joint design, cabling configuration, spatial distribution of the magnetic field, sample geometry, and experimentally determined interstrand resistance distributions have been taken into account. Although unable to predict the quench point due to the lack of a thermal-hydraulic routine, the model allows to assess the instantaneous strand power at quench and its local distribution in the cable once the quench conditions in terms of current and temperature are experimentally known. The analysis points out the relation of the above mentioned factors with the DC quench stability of both short samples and coils. The possible small scale and local electrical-thermal interactions were ignored in order to examine the relevance of such effects in the overall prediction of the CICC performance. The electromagnetic code shows an excellent quantitative predictive potential for CICC transport properties, excluding any freedom for matching the results. The influence of the local thermal effects in the modeling is identified as being marginal and far less than the generally accepted temperature margin for safe operation.
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85.25.Am Superconducting device characterization, design, and modeling
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
84.71.Ba Superconducting magnets; magnetic levitation devices
84.71.Fk Superconducting cables

Electromagnetic and absorption properties of urchinlike Ni composites at microwave frequencies

T. Liu, P. H. Zhou, J. L. Xie, and L. J. Deng

J. Appl. Phys. 111, 093905 (2012); http://dx.doi.org/10.1063/1.4709727 (5 pages)

Online Publication Date: 2 May 2012

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In this paper, nearly monodispersed urchinlike Ni powders were synthesized by a simple hydrogen-thermal reduction method. Electromagnetic and absorption characteristics were then investigated at 0.5–18 GHz. The permeability spectra present four resonance peaks over the whole frequency range. The resonance absorption property was discussed by fitting the permeability spectrum using the well-known Landau-Lifshitz-Gilbert equation and Maxwell-Garnett mixing rule. Correspondingly, the magnetic loss of the first band observed is attributed to the natural resonance, while the other three bands are considered to originate from non-uniform exchange resonance in the permeability spectra. The maximum reflection loss can reach −43 dB at about 10 GHz with 2 mm in absorber thickness.
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81.10.Dn Growth from solutions
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Influence of oxygen vacancies on the electronic structure and magnetic properties of NiFe2O4 thin films

G. Hassnain Jaffari, A. K. Rumaiz, J. C. Woicik, and S. Ismat Shah

J. Appl. Phys. 111, 093906 (2012); http://dx.doi.org/10.1063/1.4704690 (6 pages) | Cited 1 time

Online Publication Date: 2 May 2012

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We report stabilization of magnetic glassy state in non-stoichiometric nickel ferrite thin films prepared by pulse laser deposition. Details of electronic structure of the films are presented and compared with stoichiometric bulk counterpart. Hard x-ray photoelectron spectroscopy shows significant amount of oxygen vacancies and enhanced cationic inversion for thin films. Films show spin glass (SG) features which is contrary to the usual ferrimagnetic response of the bulk nickel ferrite. Films exhibit spin freezing temperature which is above room temperature in low fields (0.1 T) and shifts to lower temperature (∼250 K) in the presence of a large applied field of 3 T. An exceptionally large exchange bias (EB) of 170 Oe at a significantly higher temperature (∼50 K) is measured in cooling field of 3 T. In comparison, bulk samples do not show exchange bias and magnetic irreversibility vanishes in significantly weaker fields (i.e., few kOe). Role of oxygen vacancies is to induce spin canting by destabilizing indirect super exchange interaction. Consequently, the spin-glass like behavior occurs that is coupled with huge suppression in saturation magnetization in the thin films. Observation of exchange bias is explained to be due to oxygen vacancies (hence non-stoichiometry) which generates random anisotropy in exchange coupled grains.
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75.70.Ak Magnetic properties of monolayers and thin films
71.20.Ps Other inorganic compounds
75.30.Et Exchange and superexchange interactions
79.60.Dp Adsorbed layers and thin films
75.50.Gg Ferrimagnetics
81.15.Fg Pulsed laser ablation deposition

A simulation study of magnetic force effects on solution flow during protein crystal growth

H. Okada, N. Hirota, S. Matsumoto, and H. Wada

J. Appl. Phys. 111, 093907 (2012); http://dx.doi.org/10.1063/1.4709724 (6 pages) | Cited 1 time

Online Publication Date: 3 May 2012

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We are developing a superconducting magnet system for growing high-quality protein crystals from solutions in a reduced gravity environment by magnetic force. In order to estimate a suitable reduced gravity environment by magnetic force for protein crystal growth, we propose a flow simulation model that elucidates the motion of multicomponent solutions under magnetic force. The simulation model is based on the Navier-Stokes equation and is applied to analyzing effects of different factors on the fluid flow in protein solutions. Numerical calculation results indicate that magnetic force strongly influences the protein solution flow through magnetic susceptibility distribution in fluid.
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87.15.N- Properties of solutions of macromolecules
47.10.ad Navier-Stokes equations

Interface and oxide quality of CoFeB/MgO/Si tunnel junctions

Jonathan T. Shaw, H. W. Tseng, Shantanu Rajwade, Lieh-Ting Tung, R. A. Buhrman, and Edwin C. Kan

J. Appl. Phys. 111, 093908 (2012); http://dx.doi.org/10.1063/1.4709766 (5 pages)

Online Publication Date: 3 May 2012

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CoFeB/MgO/Si MOS capacitors were characterized to study the oxide and interface quality of very thin MgO layer (< 2 nm) after various annealing protocols. The improvement in tunneling magneto-resistance (TMR) ratio of a CoFeB/MgO/CoFeB composite layer is believed to result from boron (B) diffusion into the MgO layer to form a polycrystalline Mg-B-O layer, which has a much sharper interface after annealing. By studying the stress-induced-leakage current and the oscillating component of the tunneling current in these MOS structures, we were able to monitor the trap density, interface quality, and endurance of the dielectric. With the CoFeB capping layer, the dielectric defect density is indeed smaller after annealing, which may help to explain the enhancement in TMR. While thermal annealing results in a sharper interface and superior endurance quality with the capping layer, the interface trap density is only marginally improved with annealing.
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84.32.Tt Capacitors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.40.Gh Other heat and thermomechanical treatments

Growth of sputter-deposited metamagnetic epitaxial Ni-Co-Mn-In films

R. Niemann, L. Schultz, and S. Fähler

J. Appl. Phys. 111, 093909 (2012); http://dx.doi.org/10.1063/1.4712310 (6 pages) | Cited 1 time

Online Publication Date: 4 May 2012

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Metamagnetic thin films represent a promising geometry for more efficient magnetocaloric cooling applications due to a fast heat transfer. Here, we identify suitable growth conditions to obtain epitaxial Ni-Mn-In-Co films with a metamagnetic transition in vicinity of room temperature. We show that both increased substrate temperature and target aging result in loss of indium. This can be attributed to evaporation and preferential sputtering, respectively. We present a model that treats the effect of target aging and temperature dependence of evaporation on the film composition independently and enables predictions of the film composition as a function of initial target composition, target age, and deposition temperature. Furthermore, our analysis reveals that a sufficient degree of chemical B2 order is required for a transformation, in addition to an appropriate film composition.
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81.15.Cd Deposition by sputtering
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
68.55.A- Nucleation and growth
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
81.05.Bx Metals, semimetals, and alloys

Texture-induced magnetic interactions in ferrofluids

A. Urtizberea, A. Arizaga, N. J. O. Silva, A. Millán, F. Palacio, and F. Luis

J. Appl. Phys. 111, 093910 (2012); http://dx.doi.org/10.1063/1.4709725 (6 pages) | Cited 2 times

Online Publication Date: 4 May 2012

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We report a method for reversibly controlling the strength of dipole-dipole interactions in maghemite ferrofluids. In order to induce some magnetic texture, the ferrofluid is exposed to a strong magnetic field while it is cooled from room temperature to below its freezing temperature. The experimental data show that the average strength of dipolar interactions increases with increasing texture and that the magnetic relaxation becomes slower.
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75.75.Cd Fabrication of magnetic nanostructures
75.75.Jn Dynamics of magnetic nanoparticles
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Mm Magnetic liquids
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Wx Nanopowders

Transport properties of high-performance all-Heusler Co2CrSi/Cu2CrAl/Co2CrSi giant magnetoresistance device

Z. Q. Bai, Y. H. Lu, L. Shen, V. Ko, G. C. Han, and Y. P. Feng

J. Appl. Phys. 111, 093911 (2012); http://dx.doi.org/10.1063/1.4712301 (4 pages) | Cited 1 time

Online Publication Date: 7 May 2012

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Transport properties of giant magnetoresistance (MR) junction consisting of trilayer Co2CrSi/Cu2CrAl/Co2CrSi Heusler alloys (L21) are studied using first-principles approach based on density functional theory and the non-equilibrium Green's function method. Highly conductive channels are found in almost the entire k-plane when the magnetizations of the electrodes are parallel, while they are completely blocked in the antiparallel configuration, which leads to a high magnetoresistance ratio (the pessimistic MR ratio is nearly 100%). Furthermore, the calculated I-V curve shows that the device behaves as a good spin valve with a considerable disparity in currents under the parallel and antiparallel magnetic configurations of the electrodes. The Co2CrSi/Cu2CrAl/Co2CrSi junction could be useful for high-performance all-metallic current-perpendicular-to-plane giant magnetoresistance reading head for the next generation high density magnetic storage.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Superconductivity in fluorine and yttrium co-doped SmFeAsO

K. T. Lai, F. L. Kwong, and Dickon H. L. Ng

J. Appl. Phys. 111, 093912 (2012); http://dx.doi.org/10.1063/1.4712309 (5 pages) | Cited 1 time

Online Publication Date: 7 May 2012

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Polycrystalline fluorine and yttrium co-doped SmFeAsO samples are synthesized by solid state sintering and their physical properties are studied. The lattice parameters of the Sm1−yYyFeAsO0.8F0.2 samples decrease with the increasing y due to the smaller Y ions and the stiffness of the Y-O bond. The maximum critical temperature Tc of the samples is at y = 0.05. This may be due to the fact that the strong interaction between Sm and Fe of the Fe-As bond is being re-disturbed by the doped Y ions.
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74.25.Ld Mechanical and acoustical properties, elasticity, and ultrasonic attenuation
74.62.Dh Effects of crystal defects, doping and substitution
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dq Other elastic constants
61.66.Fn Inorganic compounds

Transport and switching behaviors in magnetic tunnel junctions consisting of CoFeB/FeNiSiB hybrid free layers

D. H. Kim, D. K. Kim, J. U. Cho, S. Y. Park, S. Isogami, M. Tsunoda, M. Takahashi, E. E. Fullerton, and Y. K. Kim

J. Appl. Phys. 111, 093913 (2012); http://dx.doi.org/10.1063/1.4709738 (4 pages) | Cited 1 time

Online Publication Date: 7 May 2012

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We report the efficacy of CoFeB/FeNiSiB hybrid ferromagnetic layers as free layers in magnetic tunnel junctions. A junction with a CoFeB (2.25 nm)/FeNiSiB (0.75 nm) free layer exhibited a tunneling magnetoresistance ratio and a resistance-area product value of 130% and 25 Ωμm2, respectively. The critical current density for spin transfer torque (STT) switching was 2.3 MA/cm2. This study suggests that the addition of an amorphous FeNiSiB in the free layer enhances the magnetotransport properties.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.At Metal and metallic alloys
75.47.Np Metals and alloys
75.50.Bb Fe and its alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Magnetic properties and magnetocaloric effect in intermetallic compounds NdMn2−xCoxSi2

S. M. Yusuf, Madhumita Halder, A. K. Rajarajan, A. K. Nigam, and S. Banerjee

J. Appl. Phys. 111, 093914 (2012); http://dx.doi.org/10.1063/1.4709761 (8 pages)

Online Publication Date: 7 May 2012

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We report magnetic properties and magnetocaloric effect in intermetallic compounds NdMn2−xCoxSi2 (x = 0.2, 0.4, 0.6, 0.8, and 1). dc magnetization study shows that these compounds undergo a ferromagnetic-like transition at around 45 K. Neutron diffraction study at 5 K for the x = 0.2 sample shows a canted-ferromagnetic state at lower temperature (5 K), and a collinear antiferromagnetic state at higher temperature (above ∼50 K). At 5 K, the Nd moments are aligned along the crystallographic c-axis and the Mn moments are canted to the c-axis. At higher temperatures (50, 100, 200, and 300 K), Nd sublattice does not order but Mn sublattice orders antiferromagnetically. A magnetocaloric effect (MCE) is found with a magnetic entropy change of 14.4 and 12.4 J kg−1 K−1 for the x = 0.2 and 0.4 samples, respectively, at 47.5 K under a field variation of 50 kOe. Various interesting phenomena such as metamagnetic transitions and domain wall pinning have been observed, and their role in obtaining a large MCE and an inverse MCE, respectively, has been brought out. The hysteresis (in magnetic field dependent dc magnetization study) reduces significantly at temperatures near and above the magnetic transition temperature (TC), which makes these materials important for their practical applications in magnetic refrigeration around TC.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Thickness dependent magnetic properties of amorphous FeTaC films

Akhilesh K. Singh, Bhagaban Kisan, Debabrata Mishra, and A. Perumal

J. Appl. Phys. 111, 093915 (2012); http://dx.doi.org/10.1063/1.4710531 (7 pages)

Online Publication Date: 7 May 2012

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We report on the study of thickness and temperature dependent magnetic properties of amorphous FeTaC (t = 20–200 nm) thin films prepared on thermally oxidized Si substrate at ambient temperature. Room temperature coercivity remains constant (∼1.5 Oe) for t between 20 and 50 nm, but increases rapidly (>18 Oe) when t > 50 nm. Also, the shape of M-H loop changes from rectangular to flat loop with increasing film thickness; and at larger thicknesses (>50 nm), the central range of constant slope in the flat loop extended largely along with the enlargement of hysteresis around the origin. This is mainly due to the development of perpendicular anisotropy with increasing the film thickness causing a transition from in-plane orientations of the spins to a magnetic stripe domain structure, which degrades the magnetic properties at larger thickness. Low temperature thermomagnetization curves obtained under zero-field-cooled (ZFC) and field-cooled (FC) conditions depicts a bifurcation between ZFC and FC data at larger thickness films. With decreasing t, the bifurcation point shifted to lower temperatures and almost disappeared for t ≤ 50 nm. On the other hand, the high temperature magnetization data reveal a considerable increase in Curie temperature with decreasing film thickness and the magnetic susceptibility critical exponent γ exhibits a thickness dependent behavior. The observed results are discussed on the basis of two-layer model, and the development of perpendicular anisotropy and magnetic disorder with increasing FeTaC film thickness.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

High magnetic field study of the Gd-Co exchange interactions in GdCo12B6

O. Isnard, Y. Skourski, L. V. B. Diop, Z. Arnold, A. V. Andreev, J. Wosnitza, A. Iwasa, A. Kondo, A. Matsuo, and K. Kindo

J. Appl. Phys. 111, 093916 (2012); http://dx.doi.org/10.1063/1.4710995 (5 pages) | Cited 1 time

Online Publication Date: 7 May 2012

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Pulsed magnetic fields up to 68 Tesla have been used to determine the intersublattice coupling strength and its temperature dependence of GdCo12B6 compound. This compound exhibits ferrimagnetic behaviour below 163 ± 2 K. Two antiferromagnetically coupled sublattices cancel out at compensation temperature at about 48 K. They are carrying magnetization of typically 0.42 μB/Co atom and 7 μB/Gd. The intrinsic magnetic properties of the GdCo12B6 compound have been determined by combining low temperature magnetic measurements in both steady and pulsed magnetic field, as well as isofield studies in steady field. At 4.2 K, the magnetization curve of GdCo12B6 is found to reach the full saturation with sum of both sublattice magnetizations for an applied magnetic field of about 68 T. In addition a detailed study is presented in the whole ordered temperature range on the basis of magnetization curves recorded using pulsed magnetic field up to 60 T. This has enabled to investigate the intersublattice coupling strength and its temperature dependence, a value JCo-Gd/kB = −5.3 ± 0.3 K is derived from the magnetization curves whereas one gets much larger value for JCo-Co/kB = 108 K.
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75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Direct calculation of the attempt frequency of magnetic structures using the finite element method

G. Fiedler, J. Fidler, J. Lee, T. Schrefl, R. L. Stamps, H. B. Braun, and D. Suess

J. Appl. Phys. 111, 093917 (2012); http://dx.doi.org/10.1063/1.4712033 (7 pages) | Cited 3 times

Online Publication Date: 10 May 2012

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A numerical implementation of the transition state theory is presented which can be used to calculate the attempt frequency f0 of arbitrary shaped magnetic nanostructures. The micromagnetic equations are discretized using the finite element method. The climbing image nudged elastic band method is used to calculate the saddle point configuration, which is required for the calculation of f0. Excellent agreement of the implemented numerical model and analytical solutions is obtained for single domain particles. The developed method is applied to compare f0 for single phase and graded media grains of advanced recording media. f0 is predicted to be comparable if the maximum anisotropy is the same in these two media types.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.75.Fk Domain structures in nanoparticles
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure

Ferromagnetism in ZrFe12−xAlx and HfFe12−xAlx (x = 6.0, 6.5, 7.0)

Michael A. McGuire, Nirmal Ghimire, and David J. Singh

J. Appl. Phys. 111, 093918 (2012); http://dx.doi.org/10.1063/1.4712445 (6 pages) | Cited 1 time

Online Publication Date: 10 May 2012

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Results of crystal structure, microstructure, and magnetic properties studies of arcmelted and annealed ZrFe6Al6, ZrFe5.5Al6.5, ZrFe5Al7, HfFe6Al6, HfFe5.5Al6.5, and HfFe5Al7 are reported. These compounds adopt the ThMn12 structure-type (space group 139, I4/mmm), like their more common rare-earth analogues. Analysis of powder x-ray diffraction data show that the 8f site is occupied by Fe, the 8i site by Al, and the 8j site by a mixture of Fe and Al. All of the compounds undergo a ferromagnetic transition at temperatures ranging from 170 to 270 K. Three effects on the magnetic properties are noted as the Fe content is increased: decrease in the Curie temperature, decrease in the magnetic moment per Fe at high fields, and the development of non-monotonic temperature dependence of the low-field magnetization below the Curie temperature. First principles calculations indicate a ferromagnetic ground state, but find antiferromagnetic interactions among Fe moments on 8j sites which is likely important in understanding the observed behavior.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Dk Alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics

Diluted antiferromagnet effect on magnetic and microwave characteristics of exchange-biased multilayered thin films

Nguyen N. Phuoc and C. K. Ong

J. Appl. Phys. 111, 093919 (2012); http://dx.doi.org/10.1063/1.4712532 (7 pages) | Cited 1 time

Online Publication Date: 10 May 2012

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A comprehensive experimental study of the effect of antiferromagnetic (AF) dilution on the magnetic properties and microwave characteristics of Fe70Co30/(Mn75Ir25)1−x(Al2O3)x multilayered thin films with the variation of AF thickness was performed. Our result reveals a linear relationship between the critical AF thickness and the dilution of the AF layers providing an evidence of a volume effect in the AF layers consistent with the domain state model. The AF magnetic anisotropy deduced from the critical AF thickness was found to reduce monotonically with the AF dilution. The variations of exchange bias, rotational magnetic anisotropy, ferromagnetic resonance frequency, and effective damping factor with the AF dilution and thickness have also been presented and discussed.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.50.Ee Antiferromagnetics
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Et Exchange and superexchange interactions

Voltage response of non-uniform arrays of bi-superconductive quantum interference devices

Patrick Longhini, Susan Berggren, Anna Leese de Escobar, Antonio Palacios, Sarah Rice, Benjamin Taylor, Visarath In, Oleg A. Mukhanov, Georgy Prokopenko, Martin Nisenoff, Edmond Wong, and Marcio C. De Andrade

J. Appl. Phys. 111, 093920 (2012); http://dx.doi.org/10.1063/1.4712039 (14 pages)

Online Publication Date: 11 May 2012

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Multi-loop arrays of Josephson junctions (JJs) with non-uniform area distributions, which are known as superconducting quantum interference filters (SQIFs), are the most highly sensitive sensors of changes in applied magnetic field as well as the absolute magnitude of magnetic fields. The non-uniformity of the loop sizes allows the array to produce a unique collective voltage response that has a pronounced single peak with a large voltage swing around zero magnetic field. To obtain high linear dynamic range, which is critical for a wide variety of applications, the linearity of the slope of the anti-peak response must be improved. We propose a novel scheme for enhancing linearity—a new configuration combining the SQIF array concept with the recently introduced bi-superconductive quantum interference device (SQUID) configuration, in which each individual SQUID loop is made up of three JJs as opposed to using two JJs per loop in standard dc SQUIDs. We show, computationally, that the additional junction offers a viable linearization method for optimizing the voltage response and dynamic range of SQIF arrays. We have realized SQIF arrays based on bi-SQUID cells and present first experimental results.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)

Effects of media stray field on electromigration characteristics in current-perpendicular-to-plane giant magnetoresistance spin-valve read sensors

Ding Gui Zeng, Kyoung-il Lee, Kyung-Won Chung, and Seongtae Bae

J. Appl. Phys. 111, 093921 (2012); http://dx.doi.org/10.1063/1.4712059 (10 pages)

Online Publication Date: 11 May 2012

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Effects of magnetic stray field retrieved from both longitudinal and perpendicular magnetic recording media (denoted by “media stray field”) on electromigration (EM) characteristics of current-perpendicular-to-plane (CPP) giant magnetoresistance spin-valve (GMR SV) read sensors have been numerically studied to explore the electrical and magnetic stability of the read sensor under real operation. The mean-time-to-failure (MTTF) of the CPP GMR SV read sensors was found to have a strong dependence on the physical parameters of the recording media and recorded information status, such as the pulse width of media stray field, the bit length, and the head moving velocity. According to the numerical calculation results, it was confirmed that in the longitudinal media, the shorter the stray field pulse width (i.e., the sharper the media transition) allows for the longer MTTF of the CPP GMR SV read sensors; while in the perpendicular media, the sharper the media transition gives rise to a shorter MTTF. Interestingly, it was also revealed that the MTTF could be improved by reducing the bit length as well as increasing the head velocity in both longitudinal and perpendicular media. Furthermore, the bit distribution patterns, especially the number of consecutive ‘0’ bits strongly affected the MTTF of GMR SV read sensors. The strong dependences of MTTF on the media stray field during CPP GMR SV sensor operation are thought to be mainly attributed to the thermal cycling (temperature rise and fall) caused by the resistance change due to GMR effects.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Magnetism, magnetoresistance, and Shubnikov-de Haas oscillations in Na-implanted highly oriented pyrolitic graphite

R. F. Pires, P. Pureur, M. Behar, J. L. Pimentel, Jr., J. Schaf, and Y. Kopelevich

J. Appl. Phys. 111, 093922 (2012); http://dx.doi.org/10.1063/1.4709731 (6 pages)

Online Publication Date: 11 May 2012

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We report on magnetization, magnetoresistance, and Shubnikov-de Haas oscillations experiments in Na-implanted samples of highly oriented pyrolitic graphite (HOPG). Different ion fluences were applied so that samples with Na contents of 0.5, 1.0, 1.5, and 2.0 at. % were obtained in the implanted region. Ferromagnetic-like hysteresis was observed in magnetization experiments where the field was applied parallel to the graphene planes. The observed saturation moment increases systematically as a function of the implanted ion concentration up to Na 1 at. %, where it goes through a maximum before decreasing slightly towards Na 2 at. %. The planar magnetoresistance amplitude at fixed field and temperature closely correlates with the saturation magnetization data. This result suggests that the strong planar magnetoresistance in graphite is at least partially related to a spin dependent mechanism. The magnetoresistance experiments also reveal the occurrence of Shubnikov-de Haas oscillations. The characteristic frequencies and the effective masses could be estimated and do not depend on the Na concentration. The reported experiments show that the expressive enhancement observed in ferromagnetic-like response in Na-implanted HOPG is primarily due to point defects produced by the implantation process.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.sd Impurity concentration
61.72.up Other materials

Variation of the intersublattice exchange coupling due to hydrogen absorption in Er2Fe14B: A high-field magnetization study

E. A. Tereshina, I. S. Tereshina, M. D. Kuz’min, Y. Skourski, M. Doerr, O. D. Chistyakov, I. V. Telegina, and H. Drulis

J. Appl. Phys. 111, 093923 (2012); http://dx.doi.org/10.1063/1.4716007 (8 pages) | Cited 2 times

Online Publication Date: 14 May 2012

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Single crystals of a series of hydrides Er2Fe14BHx (x ≤ 2.5) have been produced and studied in pulsed magnetic fields up to 60 T. The magnetization curve of Er2Fe14B in the easy direction [100] features a stepwise anomaly at about 45 T, corresponding to the first-order phase transition. A similar magnetization jump is also present in the curve along [110], but at a higher field, ∼52 T. The [100] data of the parent and hydrogen-charged Er2Fe14BHx with x = 0.25, 1.5, 2.5 were used to deduce the Er-Fe molecular field Hmol as a function of hydrogen content x. After moderate initial decrease, Hmol(x) drops abruptly above x = 1.5. Hydrogenation results in a 12% reduction of the Er-Fe molecular field in Er2Fe14BH2.5 as compared to Er2Fe14B. For reference, influence of hydrogen on Hmol in an Er2Fe17-H system is also presented.
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75.30.Et Exchange and superexchange interactions
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
82.30.-b Specific chemical reactions; reaction mechanisms

Internal strain dependence of complex permeability of ball milled carbonyl iron powders in 2–18 GHz

Jinghua He, Wei Wang, and Jianguo Guan

J. Appl. Phys. 111, 093924 (2012); http://dx.doi.org/10.1063/1.4716028 (5 pages) | Cited 1 time

Online Publication Date: 15 May 2012

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A series of the flake-like and sphere-like nanocrystalline carbonyl-iron powders (CIPs) were prepared by high energy ball milling raw CIPs for different times (t). Variations of the structure, morphology, microwave complex permeability, and static magnetization with t for the two kinds of CIPs have been investigated using x-ray diffraction, scanning electron microscopy, vector network analyzer, and vibrating sample magnetometer, respectively. The results show that with prolonging t, the nature resonance frequency (fr) and internal strain (〈ɛ〉) increase monotonously for the sphere-like nanocrystalline CIPs, while those fluctuate for the flake-like nanocrystalline CIPs. These phenomena are in accordance with the increasing fr with increasing 〈ɛ〉, suggesting that 〈ɛ〉 suppresses the domain wall displacement and promotes the gyromagnetic spin rotation. As a result, the competition between the domain wall displacement and the gyromagnetic spin rotation can be effectively controlled by 〈ɛ〉 in the as-milled nanocrystalline CIPs.
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81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
75.75.Cd Fabrication of magnetic nanostructures
75.75.Fk Domain structures in nanoparticles
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.50.Tt Fine-particle systems; nanocrystalline materials

Perpendicular-magnetic-anisotropy CoFeB racetrack memory

Y. Zhang, W. S. Zhao, D. Ravelosona, J.-O. Klein, J. V. Kim, and C. Chappert

J. Appl. Phys. 111, 093925 (2012); http://dx.doi.org/10.1063/1.4716460 (5 pages) | Cited 3 times

Online Publication Date: 15 May 2012

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Current-induced domain wall motion in magnetic nanowires drives the invention of a novel ultra-dense non-volatile storage device, called “racetrack memory.” Combining with magnetic tunnel junctions write and read heads, CMOS integrability and fast data access speed can also be achieved. Recent experimental progress showed that perpendicular-magnetic anisotropy (PMA) CoFeB could be a good candidate to build up racetrack memory and promise high performance like high-density (e.g., ∼1 F2/bit), fast-speed, and low-power beyond classical spin transfer torque memories. In this paper, we first present the design of PMA CoFeB racetrack memory and a spice-compatible model to perform mixed simulation with CMOS circuits. Its area, speed, and power dissipation performance has been simulated and evaluated based on different technology nodes.
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85.75.Dd Magnetic memory using magnetic tunnel junctions
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
85.75.Bb Magnetic memory using giant magnetoresistance
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