Search Results - (Author, Cooperation:D. Eckert)

2015-12-04

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0028-0836

1476-4687

Biology

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2018-06-05

Rockefeller University Press

0022-1007

1540-9538

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Solid Tumors

2018-10-14

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1757-8981

1757-899X

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

1089-7550

AIP Digital Archive

Physics

Coercivities up to 1.9 T were achieved by bonding micron-size Sm2Fe17Nx particles with zinc. X-ray analysis of Zn-bonded samples indicates the presence of the ZnFe Γ phase and no unreacted Zn, after heat treatment at about 390 °C for 100 min for samples with Zn content varying from 5 to 35 wt. %. The increase of coercivity occurs only for a more intense heat treatment, e.g., at 390 °C for 300 min or 425 °C for 100 min. Differential scanning calorimetry (DSC) shows two exothermic peaks at 388 and 426 °C, but no endothermic peak related to the melting of Zn (at 419.6 °C) was observed. In dilatometric measurements two peaks were observed for the rate of length change near the same temperatures as the DSC peaks. Polarization-versus-field curves point to an additional ferromagnetic phase with (i) a Curie temperature near 180 K and (ii) 2% of the net magnetization at low temperatures. The corresponding dip in low-temperature demagnetization curves, however, is about 10% in depth. Most of the Sm2Fe17Nx grains in the demagnetized Zn-bonded magnets are multidomain. We found γ≈3.4×10−2 J/m2 and Dc≈0.3 μm for the wall energy and for the critical single-domain particle diameter, respectively.

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1089-7550

AIP Digital Archive

Physics

Two types of textured, fully dense NdFeB hydrogenation, disproportionation, desorption, and recombination (HDDR) magnets were produced. The first type was produced by hot pressing isotropic HDDR powder followed by die upsetting; the second, by hot pressing prealigned, anisotropic HDDR powder (MQA-T). Studies of the magnetization processes revealed that for isotropic HDDR powder and its hot pressed and die-upset magnets a much larger initial susceptibility is found after thermal demagnetization than after reverse dc-field demagnetization. Prealigned, hot pressed magnets made from MQA-T material showed a different virgin magnetization curve, indicating a unique coercivity mechanism. Interaction domains larger than the average grain size can be observed in both cases by Kerr microscopy, with the MQA-T type showing significantly broader interaction domains. © 2000 American Institute of Physics.

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1089-7550

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Physics

The singular point detection (SPD) technique as well as a least-mean-square procedure of fitting trial texture functions to demagnetization curves (DMC) were applied in order to determine the orientation density of the tetragonal axes of the Nd2Fe14B crystallites in sintered Nd-Fe-B magnets with different degrees of grain alignment. Both methods are less complicated than calculating the texture function from x-ray-diffraction data. The orientation densities obtained by both methods agree fairly. Analytically, they can be described as a Gaussian or a sum of cosine-power functions of the angle between the local tetragonal axis and the texture axis. This agreement is a test for the DMC method which can also be used for materials showing much larger anisotropy fields than the maximum available measuring field. The SPD and DMC methods can also be applied to measure the temperature dependence of the anisotropy field HA of the magnetic main phase in noncompletely textured polycrystalline materials. By means of the DMC method additionally the spontaneous polarization Js as well as the anisotropy constants K1 and K2 can be determined. As expected, the values of HA of our sintered Nd-Fe-B samples, measured up to 140 °C, are nearly independent of the degree of texture and are in agreement with those reported in literature. This confirms that SPD as well as DMC can be used to measure intrinsic magnetic properties for materials which can hardly be prepared as single crystals, such as interstitial compounds made by gas–solid reactions.

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1089-7550

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Physics

The effect of carbon diffusion from CH4 gas into coarse Sm2Fe17 powder on the magnetic domain structure (MDS) was studied at room temperature by means of the magneto-optical polar Kerr effect. The diffusion occurs initially along preferential paths and then through the bulk. A gradual variation in the MDS through incompletely carburized grains was observed, which reflects local changes in spontaneous magnetization and magnetic anisotropy. This suggests the existence of smooth "bathtublike'' carbon concentration profiles. An acceleration of the carburization process caused by cracking of grains during the diffusion was observed. The diffusivity R of carbon in Sm2Fe17 at 450 °C was estimated to be 2.5×10−16 m2/s. For Sm2Fe17C2.2 the domain-wall energy density is γ=3.1×10−2 J/m2, the domain-wall thickness δ=3.3 nm, the single-domain particle size Dc≈0.3 μm, and the exchange constant A=8.1×10−12 J/m.

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1089-7550

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Physics

By ball milling Sm2Fe17Nx the coercivity can be increased from 0.3 to 1.5 T. The coercivity increases continuously during milling up to a time of about 600 min, and then decreases for too intensive ball milling. This is connected to particle size reduction and other effects like the increase in oxygen content, introduction of mechanical stresses, formation of new grain boundaries, and amorphization of the material. Magnetic measurements, scanning electron microscopy, as well as domain wall observations indicate that long-time milled material is mainly constituted of single domain particles and isotropic polycrystalline particles with small grains.

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1077-3118

AIP Digital Archive

Physics

A gradual change of the grain orientation with the substrate temperature (TS) during deposition has been observed for La0.7Sr0.3MnO3 films on Y-stabilized ZrO2(100) substrates. Epitaxial growth has been found around TS(approximate)800 °C. Both the low-field and the high-field magnetoresistance (MR) observed for the ferromagnetic state of these polycrystalline colossal MR manganite films were found to systematically depend on the degree of texture. The experimental results suggest a crucial role of a highly resistive region at the grain boundaries for this MR effect. © 1999 American Institute of Physics.

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Orthorhombic Ba3Cu2O4Cl2 contains folded Cu2O4 chains along the crystallographic a direction with two different Cu sites. In single crystals of this compound the magnetization measured for a field applied parallel to the a axis shows a spin-flop transition at a threshold field of 2.6 T for temperatures below TN(approximate)20 K. Above TN a Curie–Weiss behavior is found with a paramagnetic moment of 2.0 μB per Cu atom. Parallel to the b or c axis the magnetization increases linearly with the field strength, and no metamagnetic transition was detected for these directions. It is concluded that Ba3Cu2O4Cl2 has localized magnetic moments which, at low temperatures, order antiferromagnetically parallel to the a axis. The bulklike magnetic behavior of this compound is probably caused by a strong coupling between the Cu2O4 chains. Tetragonal Ba2Cu3O4Cl2 is built up of Cu3O4 planes, also with two types of copper atoms (CuA,CuB). Its magnetization increases nearly linearly with the field. Below TNA=337 K single-crystalline Ba2Cu3O4Cl2 shows a spontaneous magnetization and ferromagnetic hysteresis for fields applied parallel to the tetragonal [100] or [110] directions. For T〈TNB(approximate)33 K, the coercive field is more than one order of magnitude larger compared to that measured in the temperature range TNB〈T〈TNA. The spontaneous magnetization observed in TNB〈T〈TNA may be attributed to weak ferromagnetism of the Dzyaloshinsky–Moriya type. The behavior of Ba2Cu3O4Cl2 at lower temperatures, T≤TNB, is not yet understood. © 1998 American Institute of Physics.

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We have investigated the magnetic properties of La0.7Sr0.3MnO3(LSMO)/SrTiO3(STO) superlattices on a number of samples with the thickness dLSMO≥dSTO in order to understand the interface magnetism and the possible interlayer magnetic coupling. A series of multilayers with several thickness combinations of dLSMO and dSTO, varying from 1.9 to 10 nm was fabricated on SrTiO3(100) substrates by pulsed laser deposition. A ferromagnetic transition was observed for all studied films and the transition temperature decreased with dLSMO, without showing a clear dependence on dSTO. The spontaneous magnetization was found to decrease with dLSMO though the decrease is not as strong as expected for a magnetically disordered surface of the LSMO layers. © 2001 American Institute of Physics.

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1077-3118

AIP Digital Archive

Physics

High coercivities μ0iHC of 1.8 and 2.0 T, twice as high as previously reported, remanences Br of 0.63 and 0.69 T, and maximum energy products (BH)max of 70 and 89 kJ/m3 at 293 K are achieved for Nd13Dy2Fe77C8−xBx ribbons with x=0 and 2 after optimum heat treatment, respectively. The samples prepared by rapid quenching and short-time vacuum annealing are of tetragonal Nd2Fe14B (2:14:1)-type structure. It was confirmed that boron addition accelerates the formation of the 2:14:1-type structure, which is formed directly from melt spinning. A very high coercivity of 2.5 T was observed for as-quenched Nd13Dy2Fe77C6B2 ribbons, however with poorer B–H-loop shape. © 2000 American Institute of Physics.

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1089-7550

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Physics

The microscopic origin of ferromagnetic ordering as well as the existence of hysteresis in TDAE-C60 are contradictorily discussed in the literature. At 1.7 K the zero-field magnetization, M(0), extrapolated from the demagnetization curve of a TDAE-C60 powder, is only a small fraction of the saturation magnetization Ms(approximate)1.2 A m2/kg (or emu/g) measured at a field of 4 MA/m. The small value of M(0)/Ms may be due to (i) a large amount of small superparamagnetic particles and/or (ii) alignment of a canted magnetic structure at high field. After leaving TDAE-C60 powder in a sealed quartz tube with He for eight weeks this ratio increased from about 8% to 65% but Ms remained unchanged. This observation points to agglomeration of superparamagnetic clusters increasing the contribution to the ferromagnetic behavior. Typical extrinsic magnetic quantities describing a ferromagnetic material, such as remanence Mr, coercivity JHc and viscosity S, have also been measured. For temperatures 10, 5, and 1.7 K typical values of Mr and JHc are 30, 90, 200 μT, and 50, 110, and 200 A/m, respectively. The values of coercivity have the order of magnitude of those of low-carbon steel (at room temperature). After leaving a pressed TDAE-C60 sample in a sealed quartz tube with He for six weeks Mr increased and JHc decreased, both by about 30%. The samples show a logarithmic time-dependence of magnetization ΔM=−S ln(1+t/t0) with large values of the viscosity S. In the remanent state (at H=0) the measured values of S/Mr are 0.025, 0.021, and 0.019 for T=10, 5, and 2.5 K, respectively. © 1997 American Institute of Physics.

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0921-4534

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

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0921-4534

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

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0921-4534

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

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0921-4534

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

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0921-4534

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0921-4534

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

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0921-4534

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

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