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15 Feb 2012

Volume 111, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 043501 (2012); http://dx.doi.org/10.1063/1.3680881 (8 pages)

Gregory J. McGraw and Stephen R. Forrest
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back to top Magnetism and Superconductivity

Influence of the magnetization damping on dynamic hysteresis loops in single domain particles

Gabriel T. Landi

J. Appl. Phys. 111, 043901 (2012); http://dx.doi.org/10.1063/1.3684629 (13 pages) | Cited 6 times

Online Publication Date: 16 February 2012

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This article reports on the influence of the magnetization damping on dynamic hysteresis loops in single-domain particles with uniaxial anisotropy. The approach is based on the Néel–Brown theory and the hierarchy of differential recurrence relations, which follow from averaging over the realizations of the stochastic Landau–Lifshitz equation. A new method of solution is proposed, where the resulting system of differential equations is solved directly using optimized algorithms to explore its sparsity. All parameters involved in uniaxial systems are treated in detail, with particular attention given to the frequency dependence. It is shown that in the ferromagnetic resonance region, novel phenomena are observed for even moderately low values of the damping. The hysteresis loops assume remarkably unusual shapes, which are also followed by a pronounced reduction of their heights. Also demonstrated is that these features remain for randomly oriented ensembles and, moreover, are approximately independent of temperature and particle size.
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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.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.78.-n Magnetization dynamics

Evidence for low temperature glassy behavior in La0.5Sr0.5CoO3

D. Samal and P. S. Anil Kumar

J. Appl. Phys. 111, 043902 (2012); http://dx.doi.org/10.1063/1.3684610 (4 pages) | Cited 4 times

Online Publication Date: 17 February 2012

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We report the observed low temperature spin glass like feature in the optimally doped La0.5Sr0.5CoO3 ferromagnetic system. The characteristic of glassy behavior has been identified by noting (i) the frequency-dependent shift of the low temperature hump position in the out of phase ac susceptibility component; (ii) evolution of freezing temperature with dc biasing field that adheres to de Almeida–Thouless relation; (iii) memory effect; and (iv) sluggish magnetic relaxation. The results of magnetic measurements demonstrate that neither the inter-cluster interaction nor the spin disorder at the interface between ferromagnetic clusters is responsible for the manifestation of such collective glassy behavior. Rather, it is believed to arise from a distinct cluster glass like phase that possibly coexists with the dominant ferromagnetic phase.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Lk Spin glasses and other random magnets
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Sg Magnetocaloric effect, magnetic cooling

59Co nuclear magnetic resonance study of the local distribution of atoms in the Heusler compound Co2FeAl0.5Si0.5

Sabine Wurmehl, Jürgen T. Kohlhepp, Henk J. M. Swagten, and Bert Koopmans

J. Appl. Phys. 111, 043903 (2012); http://dx.doi.org/10.1063/1.3684686 (8 pages)

Online Publication Date: 17 February 2012

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In this work, the spin-echo nuclear magnetic resonance (NMR) technique is used to probe the local structure of Co2FeAl0.5Si0.5 bulk samples. The 59Co NMR spectrum of the Heusler compound Co2FeAl0.5Si0.5 consists of four main resonance lines with an underlying sub-structure. The splitting into the main resonance lines is explained by contributions of the B2 type structure. The sub-lines are attributed to a random distribution of Al and Si. By comparing the experimental results with an appropriate multinomial distribution, the fraction of the Al/Si intermixing and the ratio between the contributing structure types is assigned. The main structural contribution of as-cast bulk samples is of B2 type with 38% of L21 contributions. The L21 contribution can be enhanced to 59% by an appropriate annealing process. However, B2 contributions are still present after annealing. Additional foreign phases such as fcc-Co and Co-Al, with relative contributions of less than one percent, are also found in both as-cast and annealed samples. Resonance lines related to slight amounts of the ternary, parental Heusler compounds Co2FeAl and Co2FeSi are also observed.
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76.60.Lz Spin echoes
61.66.Dk Alloys
64.75.Ef Mixing
81.40.Gh Other heat and thermomechanical treatments

Low-temperature magnetization curves of anisotropic ferrimagnets

M. D. Kuz’min

J. Appl. Phys. 111, 043904 (2012); http://dx.doi.org/10.1063/1.3687424 (8 pages)

Online Publication Date: 21 February 2012

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Anisotropic ferrimagnets—unlike isotropic ones—exhibit a rich variety of shapes of magnetization curves. The possibilities are analyzed in an exhaustive fashion within a model with second-order anisotropy on both sublattices, limited to low temperatures and high-symmetry orientations of the applied magnetic field. It is important to discriminate between ferrimagnets with grossly unequal sublattices (when the moments differ by a factor of 2 or more) and those whose sublattice moments are relatively close, i.e., differ by less than a factor of 2. In the former case, as many as 10 different curve shapes are possible; in the latter case, only 9. For a given compound and field direction, the shape is determined by the system’s locus in the coordinate plane of reduced anisotropy parameters. For any ratio of the sublattice moments, such a diagram is obtainable by means of analytic expressions.
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75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities

The study of negative thermal expansion and magnetic evolution in antiperovskite compounds Cu0.8-xSnxMn0.2NMn3(0 ≤ x ≤ 0.3)

J. C. Lin, B. S. Wang, S. Lin, P. Tong, W. J. Lu, L. Zhang, W. H. Song, and Y. P. Sun

J. Appl. Phys. 111, 043905 (2012); http://dx.doi.org/10.1063/1.3684653 (6 pages) | Cited 1 time

Online Publication Date: 21 February 2012

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With increasing the substitution of Sn for Cu in Cu0.8-xSnxMn0.2NMn3, the initial cubic-tetragonal structural phase transition disappears for the samples x ≥ 0.10 and is replaced by a discontinuous lattice expansion with a cubic structure which has been confirmed by the measurements of variable temperature x-ray diffractions and specific heat. The discontinuous lattice expansion broadens with increasing the doping level x and the negative thermal expansion coefficient up to −64.54 ppm/K between 190 K and 235 K is found for the sample x = 0.3. Detailed magnetic measurements indicate that the magnetic ground state is meta-stable for the lower-doping level and transforms into spin-glass-like state owing to the enhancement of antiferromagnetic interaction when x is up to 0.3. Furthermore, the magnetization curves M(T) display abnormal behaviors for lower-x. For the samples x = 0.1 and 0.2, the jump of field-cooled magnetization curve MFC (defined as ΔMFC/MFC) around the lower-temperature magnetic transition is suppressed with increasing the magnetic field. These abnormalities of magnetizations are also discussed based on a simple model.
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65.40.De Thermal expansion; thermomechanical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
65.40.Ba Heat capacity
61.66.Fn Inorganic compounds
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics

Field-induced changes in polarization and magnetization in Tb0.3Dy0.7Fe2/PZT laminate composite

Hui Zhang

J. Appl. Phys. 111, 043906 (2012); http://dx.doi.org/10.1063/1.3684984 (6 pages)

Online Publication Date: 21 February 2012

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We have presented a theoretical model to describe the magnetoelectric coupling in Tb0.3Dy0.7Fe2/PZT laminate composite material. In this model, the stresses introduced by the magnetic field or electric field in the composite material are assumed to be the axial force. The magnetization of magnetostrictive phase can indirectly couple with the electrical polarization of piezoelectric phase through the stresses. The numerical results have shown that both the magnetic field and electric field can cause significant changes in the magnetization and electric polarization in the composite material.
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75.80.+q Magnetomechanical effects, magnetostriction
81.40.Lm Deformation, plasticity, and creep
77.65.Bn Piezoelectric and electrostrictive constants
77.22.Ej Polarization and depolarization
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.85.+t Magnetoelectric effects, multiferroics

Magnetic behavior of Mn-doped GaN (1math00) film from first-principles calculations

GuiQin Huang and JiXia Wang

J. Appl. Phys. 111, 043907 (2012); http://dx.doi.org/10.1063/1.3685901 (5 pages) | Cited 2 times

Online Publication Date: 21 February 2012

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Using first principles calculations based on spin-polarized density functional theory, the magnetic behavior of Mn-doped GaN (1math00) film is studied. The doping Mn atoms have an attractive pair interaction. Our results give the ground state with antiferromagnetic coupling for Mn-doped GaN (1math00) film when the nearest neighbor Ga atoms on the surface layer are replaced by Mn atoms, which is contrary to the ferromagnetic coupling when Mn is doped in the bulk GaN. However, in-plane tension and hole doping can switch the magnetic ordering from antiferromagnetism to ferromagnetism, which is important for application in semiconductor spintronics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.uj III-V and II-VI semiconductors
75.40.Mg Numerical simulation studies
75.50.Pp Magnetic semiconductors
75.50.Ee Antiferromagnetics

Axial and lateral lattice strain states under a tensile load in as-reacted and prebent CuNb/Nb3Sn wires using neutron diffraction

K. Takahashi, H. Oguro, G. Nishijima, S. Awaji, K. Watanabe, S. Harjo, and K. Aizawa

J. Appl. Phys. 111, 043908 (2012); http://dx.doi.org/10.1063/1.3686692 (5 pages)

Online Publication Date: 22 February 2012

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Internal lattice strains under a tensile load for CuNb/Nb3Sn wires with and without prebending treatment were measured directly by neutron diffraction at room temperature. In the axial direction of the wire, the residual lattice strain was changed by 0.29% to the tensile side, while, in the lateral direction, the change was 0.03% to the compressive side due to the prebending treatment. The relationships between the axial and lateral lattice strains under axial stress are almost linear with a slope of about 0.3 for both wires; however, the absolute value of the lateral lattice strain differed at the same axial lattice strain. Tensile load dependences of the axial and lateral lattice strains of Cu and Nb in the wires were also obtained. The prebending treatment was found to affect the elastic–plastic deformation behavior of Cu and to change the internal lattice strains of Nb3Sn.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
62.20.D- Elasticity
84.71.Mn Superconducting wires, fibers, and tapes
81.40.Jj Elasticity and anelasticity, stress-strain relations
74.25.Ld Mechanical and acoustical properties, elasticity, and ultrasonic attenuation

Parallel multilayer magnetoelectric composite based on (1−x)Pb(Mg1/3Nb2/3)−xPbTiO3 and Terfenol-D coupled with charge mode amplifier

Jie Jiao, Lingying Li, Bo Ren, Hao Guo, Hao Deng, Wenning Di, Xiangyong Zhao, Weiping Jing, and Haosu Luo

J. Appl. Phys. 111, 043909 (2012); http://dx.doi.org/10.1063/1.3681818 (5 pages) | Cited 1 time

Online Publication Date: 22 February 2012

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In this paper, the sources and categories of noise regarding a charge mode magnetoelectric (ME) sensor are analyzed and simulated. A series of parallel multilayer magnetoelectric composites of Terfenol-D and (1−x)Pb(Mg1/3Nb2/3)−xPbTiO3 with different numbers of layers have been developed. The high magnetoelectric charge coefficients of these composites have been measured. By coupling different parallel multilayer magnetoelectric composites with a low noise-level charge amplifier, we found that the noise equivalent magnetic induction (NEB) of the ME sensor based on the charge mode is in accordance with the theoretical prediction, and multilayers can reduce the NEB at low frequency and hardly at high frequency. At last we have established a new method of using high g31 piezoelectric material that can effectively reduce the influence of the operational amplifier voltage noise component and enhance resolution.
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07.55.-w Magnetic instruments and components
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Effect of nonmagnetic Sc ion on the intrachain coupling in spin-chain compounds Ca3Co2−xScxO6

M. Y. Ruan, Z. W. Ouyang, J. Chen, S. S. Sheng, Z. C. Xia, and L. Li

J. Appl. Phys. 111, 043910 (2012); http://dx.doi.org/10.1063/1.3686655 (4 pages) | Cited 1 time

Online Publication Date: 23 February 2012

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We have demonstrated that in Ca3Co2−xScxO6, substitution of nonmagnetic Sc3+ (S = 0) for high-spin Cotrig, even up to the solid solubility limit of x = 0.5−0.6, does not dramatically modify the intrachain ferromagnetic (FM) interaction. This is quite different from the cases of Ir- and Rh-doping, which much enhance the intrachain FM interaction, and the cases of Mn-, Fe-, and Cr-doping, which gradually reduce the intrachain FM interaction, simultaneously introducing antiferromagnetic interaction. The results of band-structure calculations of x = 0.5 are qualitatively consistent with our magnetization data.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
71.20.Ps Other inorganic compounds
61.72.up Other materials
64.75.Bc Solubility
75.50.Ee Antiferromagnetics
75.50.Dd Nonmetallic ferromagnetic materials

Influence of plastic deformation on the magnetostrictive behavior of [126]-oriented Fe–Ga alloy single crystals

Biswadeep Saha, Meenakshisundaram Ramanathan, Chai Ren, and Sivaraman Guruswamy

J. Appl. Phys. 111, 043911 (2012); http://dx.doi.org/10.1063/1.3686680 (7 pages)

Online Publication Date: 23 February 2012

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Dislocation arrays were introduced through controlled deformation of Fe–20 at. % Ga alloy single crystal samples with ⟨100⟩ and ⟨126⟩ orientations. Alloy single crystals were obtained through vertical Bridgman growth process. Magnetostriction measurements show a large decrease in magnetostriction after deforming just past the yield point when only a single slip system is operative as in the case of [126]-oriented crystal deformation. Magnetostriction values showed a much lower decrease with deformation for the case of [100]-oriented crystal deformation, where eight different slip systems were operative and consequently eight different sets of dislocation arrays are expected. The results suggest that the nature of strain modulation introduced by the dislocation arrays has a strong influence on the magnetostrictive behavior of magnetostrictive alloys.
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75.80.+q Magnetomechanical effects, magnetostriction
81.10.Fq Growth from melts; zone melting and refining
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity

Large exchange bias obtainable through zero-field cooling from an unmagnetized state in Ni-Mn-Sn alloys

B. M. Wang, Y. Liu, B. Xia, P. Ren, and L. Wang

J. Appl. Phys. 111, 043912 (2012); http://dx.doi.org/10.1063/1.3686717 (7 pages) | Cited 2 times

Online Publication Date: 24 February 2012

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We report a large unusual exchange bias effect occurred after zero-field cooling from an unmagnetized state (ZEB) in Ni-Mn-Sn alloys, in which the maximum ZEB field is about twice as large as that observed in Ni-Mn-In alloys at moderate field range (< 40 kOe). The ZEB field can be tuned by tuning the magnitude of the initial magnetization fields and its sign is strongly dependent on the direction of the initial magnetization fields. Furthermore, the ZEB effect only exists in alloys with volume fraction of superparamagnetic domains less than the percolation limitation in three-dimensional system (∼16%). The present results confirm the universality of this unusual ZEB effect and suggest that NiMn-based alloys provide a platform to obtain this unusual ZEB effect. Such ZEB effect may also exist in other systems with similar magnetic properties.
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75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.20.Ck Nonmetals
75.78.-n Magnetization dynamics
75.50.Tt Fine-particle systems; nanocrystalline materials

Effects of boron composition on tunneling magnetoresistance ratio and microstructure of CoFeB/MgO/CoFeB pseudo-spin-valve magnetic tunnel junctions

M. Kodzuka, T. Ohkubo, K. Hono, S. Ikeda, H. D. Gan, and H. Ohno

J. Appl. Phys. 111, 043913 (2012); http://dx.doi.org/10.1063/1.3688039 (3 pages) | Cited 4 times

Online Publication Date: 27 February 2012

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The effect of B concentration on the tunneling magnetoresistance (TMR) of (Co25Fe75)100−xBx/MgO/(Co25Fe75)100−xBx (x = 22 and 33) pseudo-spin-valve (P-SV) magnetic tunnel junctions (MTJs) was investigated. The TMR ratios for optimally annealed MTJs with x = 22 and 33 were 340% and 170%, respectively, at room temperature. High resolution transmission electron microscopy (HRTEM) observation showed a weaker (001) texture in the MgO barrier in the MTJ with x = 33. The bottom electrode was not fully crystallized even with a considerable amount of B in the (Co25Fe75)67B33, while good epitaxy was observed between (001) textured MgO and (Co25Fe75)78B22 electrodes.
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72.20.My Galvanomagnetic and other magnetotransport effects
82.45.-h Electrochemistry and electrophoresis
81.15.Cd Deposition by sputtering
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Composition and atomic order effects on the structural and magnetic transformations in ferromagnetic Ni–Co–Mn–Ga shape memory alloys

C. Segui and E. Cesari

J. Appl. Phys. 111, 043914 (2012); http://dx.doi.org/10.1063/1.3688019 (7 pages) | Cited 1 time

Online Publication Date: 27 February 2012

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Within a certain range of Co content, ferromagnetic Ni–Co–Mn–Ga shape memory alloys undergo martensitic transformation (MT) between ferromagnetic austenite and paramagnetic martensite. This brings about an enlarged magnetization change with respect to the ternary Ni–Mn–Ga, approaching the requirements for magnetic field-induced MT. The MT temperatures, as well as the martensite and austenite Curie temperatures, depend on composition and on the atomic order degree. Therefore, for a given composition, thermal treatments can induce different sequences of magnetic and structural transitions and consequent variation of both magnetization and transformation entropy changes. Analysis of the structural and magnetic transitions undergone by a set of selected Ni50−xCoxMn25+yGa25−y (x = 3–8, y = 5–7) alloys allows to build a phase diagram where the composition-–temperature regions for different crystallographic and magnetic states of the alloys are shown. The temperature changes produced by water quench from 1070 K and subsequent aging at 520 K modify such phase diagram, restricting the conditions under which the above-mentioned alloys show enhanced magnetization jump. Further, the effects of composition and thermal treatment on the transformation entropy change are evaluated and correlated with the magnetic contribution.
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81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
75.50.Cc Other ferromagnetic metals and alloys
75.20.En Metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Effect of site-disorder on magnetism and magneto-structural coupling in gallium ferrite: A first-principles study

Amritendu Roy, Rajendra Prasad, Sushil Auluck, and Ashish Garg

J. Appl. Phys. 111, 043915 (2012); http://dx.doi.org/10.1063/1.3688852 (7 pages) | Cited 2 times

Online Publication Date: 28 February 2012

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Show Abstract
We report a first-principles study of the magnetic properties, cation site disorder effect on magnetism and magneto-structural coupling in multiferroic gallium ferrite (GFO) using the local spin density approximation (LSDA+U) of the density functional theory. The calculation of the ground state A-type antiferromagnetic structure predicts magnetic moments consistent with the experiments while consideration of spin-orbit coupling yields a net orbital moment also in good accordance with the experiment. We find that though cation site disorder is not spontaneous in the ground state, interchange between octahedrally coordinated Fe2 and Ga2 sites is most favored in the disordered state. The results show that ferrimagnetism in GFO is primarily due to Ga-Fe site disorder such that Fe spins at Ga1 and Ga2 sites are antiferromagnetically aligned while maintaining ferromagnetic coupling between Fe spins at Ga1 and Fe1 sites as well as between Fe spins at Ga2 and Fe2 sites. Thus we are able to explain the origin of ferrimagnetism in GFO based on cation site disorder. Our calculations, further predict the presence of magneto-structural coupling in GFO which has been recently observed experimentally.
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75.85.+t Magnetoelectric effects, multiferroics
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.30.Cr Saturation moments and magnetic susceptibilities
75.40.Mg Numerical simulation studies
75.50.Ee Antiferromagnetics
75.50.Gg Ferrimagnetics
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