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15 Jan 2000

Volume 87, Issue 2, pp. 627-960

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Magnetization curves of plastically deformed Fe metals and alloys

S. Takahashi, J. Echigoya, and Z. Motoki

J. Appl. Phys. 87, 805 (2000); http://dx.doi.org/10.1063/1.371945 (9 pages) | Cited 21 times

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The hysteresis loop of plastically deformed Fe metals and alloys was measured for single crystals, polycrystalline iron, and A533B steel samples, and the dislocation density and structure of these samples were observed by electron microscopy. The relation between structure-sensitive properties and applied stress σ was analyzed in connection with grain boundaries and dislocations. The coercive force Hc increases with σ and is represented by one curve in all the samples. The magnetic susceptibility χc above the coercive field can be described by a simple relation to the magnetic field H. χc=c/H3 in a limited region of H. The parameter c depends only on lattice defects such as dislocations and the grain size and has a simple relation to them, but is independent of the kinds of samples or of the process of plastic deformation. The susceptibility χc is explained in comparison with the susceptibility χr in the range of approach to saturation. The magnetic properties c and Hc are discussed considering the dislocation density and its distribution including the effect of grain boundaries. These magnetic properties are useful for nondestructive tests of metal fatigue. © 2000 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
75.30.Cr Saturation moments and magnetic susceptibilities
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Large magnetoresistance of the polycrystalline metamagnetic layered manganite La1.2Nd0.2Sr1.6Mn2O7

K. Dörr, K.-H. Müller, L. Schultz, K. Ruck, and G. Krabbes

J. Appl. Phys. 87, 814 (2000); http://dx.doi.org/10.1063/1.371946 (3 pages) | Cited 1 time

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Magnetization and magnetotransport have been investigated for polycrystalline samples of the bilayer Ruddlesden–Popper compound La1.2Nd0.2Sr1.6Mn2O7 that shows the colossal magnetoresistance effect connected with ferromagnetic ordering at TC=74 K. At T2=38 K the compound reveals a transition from the ferromagnetic to an antiferromagnetic spin arrangement of alternating ferromagnetic bilayers, which undergoes a first order metamagnetic transition towards ferromagnetism in a magnetic field of ∼3.5 kOe at 20 K. In measurements of resistance vs magnetic field, this transition is accompanied by a large resistance drop of [R(5 kOe)−R(0)]/R(0)=−60% at 5 K. The tunneling-like magnetoresistance (MR) known for current transport perpendicular to the layers in (La, Nd)1.4Sr1.6Mn2O7 single crystals contributes to this large MR observed in a polycrystalline sample. While current is expected to mainly follow the bilayers within the grains due to the anisotropy of conductivity, the high value of resistivity of our sample (∼8 Ω cm at 5 K) suggests that current paths are partially directed perpendicular to the layers. © 2000 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
72.60.+g Mixed conductivity and conductivity transitions
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Microstructures and magnetic properties of Co–Al–O granular thin films

M. Ohnuma, K. Hono, H. Onodera, S. Ohnuma, H. Fujimori, and J. S. Pedersen

J. Appl. Phys. 87, 817 (2000); http://dx.doi.org/10.1063/1.371948 (7 pages) | Cited 39 times

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The microstructures of Co–Al–O thin films of wide varieties of compositions are studied by transmission electron microscopy and small angle x-ray scattering (SAXS). In the superparamagnetic specimens, high resolution electron microscope images reveal that isolated spherical Co particles are surrounded by an amorphous aluminum oxide matrix. However, in the soft ferromagnetic films, the shape of the Co particles is prolate ellipsoidal. SAXS intensities from the soft magnetic specimens decrease inversely with the wave vector, q, in a low wave-vector region, while an interparticle interference peak is observed for the superparamagnetic specimens. The scattering profiles of the soft magnetic films imply that the Co particles have a cylindrical shape and are randomly oriented. The correlation between the magnetic properties and the microstructures is discussed. © 2000 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
75.50.Tt Fine-particle systems; nanocrystalline materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
78.70.Ck X-ray scattering
75.50.Cc Other ferromagnetic metals and alloys

Study of the magnetization reversal in individual nickel nanowires

S. Pignard, G. Goglio, A. Radulescu, L. Piraux, S. Dubois, A. Declémy, and J. L. Duvail

J. Appl. Phys. 87, 824 (2000); http://dx.doi.org/10.1063/1.371947 (6 pages) | Cited 52 times

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The magnetization reversal of Ni nanowires was studied by anisotropic magnetoresistance measurements at temperatures between 15 and 300 K. The wires, synthesized by electrodeposition in a nanoporous polycarbonate membrane, are regular cylinders 22 μm long with a diameter of 75 or 35 nm. The nucleation field was measured on individual nanowires as a function of the angle between the applied field and the wire axis. The results are quantitatively analyzed using classical magnetization reversal theories. Measurements of the nucleation field first obtained as a function of temperature evidence an extra uniaxial anisotropy induced by the contraction of the membrane at low temperature. Combining SQUID measurements and x-ray diffractometry at different temperatures, a clear picture of the large magnetoelastic effect was obtained. © 2000 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.30.Gw Magnetic anisotropy
75.80.+q Magnetomechanical effects, magnetostriction

Ultrahigh frequency permeability of sputtered Fe–Co–B thin films

T. J. Klemmer, K. A. Ellis, L. H. Chen, B. van Dover, and S. Jin

J. Appl. Phys. 87, 830 (2000); http://dx.doi.org/10.1063/1.371949 (4 pages) | Cited 41 times

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Amorphous FeCoB alloys can have high resistivity and relatively high saturation magnetization which are desired for ultrahigh frequency devices such as future write heads and wireless inductors. In this study, FeCoB films are observed to have a low easy axis coercivity (1–2 Oe), a field deposited induced anisotropy of ∼35 Oe and 4πMs∼17 500 G when sputtered in a typical configuration. However, samples sputtered in an off axis arrangement are found to have an additional uniaxial anisotropy as a result of the oblique incidence of the atomic flux onto the substrate. This extra anisotropy increases with increasing oblique angle. For these same samples, there is little change in the easy axis coercivity, saturation magnetization, and the Hoffmann structure factor (S∼0.05 ergs/cm2). The obtained large anisotropy fields (>35 Oe) are found to push the ferromagnetic resonance frequency to at least above 1 GHz at the expense of the initial permeability. © 2000 American Institute of Physics.
Show PACS
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Kj Amorphous and quasicrystalline magnetic materials

Magnetic and magnetostrictive properties in amorphous (Tb0.27Dy0.73)(Fe1−xCox)2 films

N. H. Duc, K. Mackay, J. Betz, and D. Givord

J. Appl. Phys. 87, 834 (2000); http://dx.doi.org/10.1063/1.371950 (6 pages) | Cited 9 times

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Magnetic and magnetostrictive properties have been investigated for amorphous (Tb0.27Dy0.73)(Fe1−xCox)2 thin films. An increase in the 3d magnetic moment due to the enhancement of T–T interactions in substituted (Fe, Co) alloys was found. This leads to stronger R–(Fe, Co) exchange energies and then to enhancements of R–sublattice magnetization as well as magnetostriction in these amorphous R(Fe, Co) thin films. In addition, a well-defined in-plane anisotropy is created by magnetic-field annealing for the Co-rich films. A large magnetostriction of 480×10−6 developed in low fields of 0.3 T was observed for films with x=0.47 after magnetic-field annealing. The differing roles of Fe and Co atoms on the magnetization process have also been discussed. © 2000 American Institute of Physics.
Show PACS
75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Nt Magnetic annealing and temperature-hysteresis effects
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.40.Gh Other heat and thermomechanical treatments
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
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