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  • 11
    Electronic Resource
    Electronic Resource
    Highly coercive SmCo5 magnets prepared by a modified hydrogenation-disproportionation-desorption-recombination process (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5666-5668 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The hydrogenation-disproportionation-desorption-recombination (HDDR) process was applied to SmCo5 using extreme conditions, namely high hydrogen pressures and reactive milling under hydrogen. Investigations on the hydrogen absorption behavior of SmCo5 by differential scanning calorimetry under hydrogen pressures between 1 and 7 MPa showed absorption events due to an interstitial absorption at about 100 °C and a disproportionation reaction at about 600 °C. X-ray diffraction showed the disproportionation of SmCo5 into Sm hydride and fcc-Co. A favorable effect of high hydrogen pressures on the disproportionation reaction was observed which can be explained by a decrease of the free enthalpy of the samarium hydride for increasing hydrogen pressures. Reactively milled SmCo5 showed also the products of the disproportionation reaction. The recombination to the original SmCo5 phase on hydrogen desorption in a subsequent heat treatment in vacuum was successful for both methods. However, Sm2O3, Sm2Co17, and Sm2Co7 were detected as minor phases. Maximum coercivities μ0JHC of 2.1 and 4.7 T were achieved for high pressure and reactively milled HDDR powders, respectively. The high coercivities originate from the high anisotropy field of the SmCo5 phase in combination with the grain refinement due to the HDDR treatment. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369834
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  • 12
    Electronic Resource
    Electronic Resource
    Growth dynamics of aluminum nitride and aluminum oxide thin films synthesized by ion-assisted deposition (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 760-769 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Some aspects of the dynamics of thin-film synthesis of aluminum nitride and aluminum oxide produced by ion-assisted deposition have been deduced from in situ measurements by ellipsometry, photometry, and ion scattering spectroscopy. Measurements obtained during the etching of aluminum films by nitrogen and oxygen ion beams have established the thickness of the synthesized layer and the rate of compound formation. Some of these measurements have been compared with a theoretical model which predicts the time evolution of the synthesized surface layer as well as the steady-state layer thickness. The breakdown voltage and variation of capacitance with applied voltage of aluminum oxide films prepared by ion-assisted deposition are also presented. Furthermore, the optical properties of ion-assisted AlN and Al2O3 in the visible region are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340068
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  • 13
    Electronic Resource
    Electronic Resource
    Hard magnetic properties of melt-spun R(Fe,M)12 nitrides (R=Nd or Pr; M=Mo or V) (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 988-992 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The hard magnetic properties of nitrided melt-spun R(Fe,M)12 (R=Pr and Nd, M=V and Mo) ribbons have been investigated. Hard magnetic powders were prepared by vacuum annealing of ground ribbons in the temperature range from 700 to 950 °C and subsequent nitrogenation. For NdFe10.5Mo1.5Nx and PrFe10.5Mo1.5Nx powders, coercivities as high as 10.4 and 4.5 kOe at room temperature, respectively, were achieved by carefully controlling the nitrogenation process. The coercivity strongly depends on the preparation route, i.e., annealing temperature as well as nitrogenation temperature and time. By the detailed investigation of the influence of these conditions, the optimum process parameters were determined. The coercivity mechanism of melt-spun NdFe10.5Mo1.5Nx powders shows characteristics of a randomly oriented single domain particle system. Poor coercivities have been obtained for Nd(Fe,V)12 and Pr(Fe,V)12. In these cases as well as for not optimally nitrogenated Nd(Fe,Mo)12, the low coercivity of the nitrided powders is related to (i) too large grain sizes, (ii) the presence of α-Fe additional to the ThMn12-type phase, or (iii) a nonhomogeneous nitrogenation of the powder. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373766
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  • 14
    Electronic Resource
    Electronic Resource
    Weak ferromagnetism in low-dimensional cuprates Ba2Cu3O4Cl2 and Ba3Cu2O4Cl2 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6022-6024 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ba2Cu3O4Cl2 is a two-dimensional quantum antiferromagnet with two Cu sublattices showing a small spontaneous magnetization M0. A group theoretical analysis shows that M0 may be due to (i) induced magnetization in the Cu II sublattice or (ii) spin canting of the Cu I moments, i.e., weak ferromagnetism (WFM). In case (i) the interaction is of pseudodipolar type. In case (ii) the Cu I moments are subject to some kind of anisotropy. The main reason for the occurrence of M0, compared to similar high-Tc cuprates related structures, is that the center between two Cu I moments is not an inversion center. Ba3Cu2O4Cl2 behaves like a classical antiferromagnet with a spin-flop transition. For this compound our analysis shows that, in the case where the magnetic and the crystallographic unit cells are identical, the Cu moments of equivalent sites should be parallel and the antiferromagnetic order is related to opposite directions of the moments at different sites. Weak antiferromagnetism but no WFM is permitted, in agreement with the experimental results. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372600
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  • 15
    Electronic Resource
    Electronic Resource
    First order magnetization processes in Nd(Fe, M)12Cy compounds (M=V, Ti, Mo) (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5278-5280 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization measurements on Nd(Fe, M)12Cy (M=Ti, V, Mo) with ThMn12-type structure have revealed well developed first order magnetization processes (FOMPs) when an external field is applied perpendicular to the c axis. The FOMPs depend on carbon concentration, temperature, and the type of M element. The FOMPs appear at a certain carbon concentration and at temperatures below 150–100 K. The FOMP fields of NdFe12−xVxCy are independent of the V content in the range x=1.25–2.0, which is due to the small change of the anisotropy field within this range. No FOMP has been found in the nitrides of the same parent alloys. The evaluation of the crystal field (CF) parameters shows that the higher-order CF parameters of the Nd ions play a key role in producing the observed type-II FOMP. The temperature dependence of the FOMPs is due to the thermal evolution of the anisotropy constants Ki (i=1,2,3) of the carbides. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373320
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  • 16
    Electronic Resource
    Electronic Resource
    Magnetization processes in two different types of anisotropic, fully dense NdFeB hydrogenation, disproportionation, desorption, and recombination magnets (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6119-6121 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372628
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  • 17
    Electronic Resource
    Electronic Resource
    Influence of Fe and Co additions on magnetization and magnetoresistivity of MnAu2 melt-spun alloys (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5789-5791 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Melt-spun MnAu2 ribbons modified by ternary magnetic additions (Fe and Co) show a large giant magnetoresistance (GMR) effect up to a magnetoresistance ratio MR={[R(H=7T)−R(0)/R(0)]} of the order of −10% at room temperature. Pure MnAu2 samples show a transition from positive magnetoresistance at low temperatures (e.g., MR=+23% at 10 K and μ0H=5 T) to a GMR behavior with values of about −8% at 295 K and 5 T. At 135 K the resistivity is nearly independent of the applied magnetic field. The strong increase of |MR| at room temperature is only found with applied fields larger than a threshold field, where a metamagnetic transition occurs. Alloying the compound with Co or Fe this threshold field can be reduced or suppressed. This effect is due to softening of the antiferromagnetic behavior of the (Mn; Co or Fe)Au2 samples. For an alloy with 5 at. % Fe as substitutes for Mn, no metamagnetic transition is observed in the temperature range between 10 and 300 K. For both 5 at. % Co or Fe additions a GMR behavior is observed in this temperature range with higher sensitivity at low fields, e.g., (Mn0.95Fe0.05)Au2 has values of MR=−12% and −1% in a field of 1 T at 10 and 295 K, respectively. At low temperatures, an anomalous increase of resistance at higher fields (above 1–2 T) is observed for these alloys. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372523
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  • 18
    Electronic Resource
    Electronic Resource
    Magnetoresistance of polycrystalline layered manganites La2−2xSr1+2xMn2O7 (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5420-5422 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polycrystalline bulk samples of the layered manganites La2−2xSr1+2xMn2O7 showing a colossal magnetoresistance (CMR) effect were prepared for doping levels of x=0.4 and 0.5 by a solid-state reaction route. Temperature and field dependences of magnetization and of electrical resistivity have been measured between 5 K and room temperature. Ferromagnetic behavior with a Curie temperature of TC=135 K and a high value of spontaneous magnetization (64 emu g−1) was found for x=0.4. The x=0.5 compound orders antiferromagnetically near TN=215 K, showing a resistivity enhancement there. The resistivity of the x=0.4 compound shows a field dependence at low temperatures similar to that found for polycrystalline La0.7Sr0.3MnO3. The resemblance includes the presence of both a low-field and a high-field contribution to the magnetoresistance, as well as the magnitude of the low-field MR (−23% at 20 K and −15% at 77 K for H=1 kOe). The low-field MR is attributed to the effect of grain boundaries. In contrast to the grain-boundary MR of La0.7Sr0.3MnO3, it was also observed at temperatures far above the TC of the layered manganite. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369962
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  • 19
    Electronic Resource
    Electronic Resource
    On the role of Zn in Sm2Fe17Nx permanent magnets : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6044-6046 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353464
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  • 20
    Electronic Resource
    Electronic Resource
    Spatiotemporal evolution of a low-pressure glow discharge (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6694-6699 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spatiotemporal evolution of a pulsed low-pressure glow discharge is investigated theoretically and experimentally. The discharge is modelled phenomenologically by a reaction-diffusion equation in which the cathode fall and the negative glow of the discharge are described as a bistable layer. A laterally one-dimensional discharge is realized experimentally by a hollow cathode discharge in a slotted cathode. With the help of probe measurements, a homogeneous evolution with a laterally uniform current rise and an inhomogeneous evolution starting from special sites and progressing along the cathode are found. The main experimental results are reproduced by model calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349843
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