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  • 2000-2004  (10)
  • 1995-1999  (25)
  • 1985-1989  (15)
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  • 1
    Digitale Medien
    Digitale Medien
    Atomic ordering and magnetic properties in Nd57Fe20B8Co5Al10 solids (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 3565-3569 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Nd57Fe20B8Co5Al10 bulk cylinders and ribbons were quenched from the melt at different cooling rates using copper mold casting and melt spinning, respectively. Both the melt-spun ribbons and the cast cylinders display x-ray diffraction patterns without obvious crystalline peaks. However, the ribbons show soft magnetic properties, the cylinders are hard magnetic, and the crystallized alloys are not ferromagnetic at all. On the other hand, the cylinders show different exothermic transformation behavior than the ribbons upon heating to elevated temperatures. While the ribbons are regarded as amorphous, the structure of the cylinders prepared at slower cooling rate is considered to consist of metastable ordered clusters. This structure forms in the undercooled melt most likely due to intensive generation of ordered nuclei and slow growth kinetics. The magnetic coherence length, which is equivalent to the dimension of the ordered clusters, may be larger than the exchange length. Therefore, the cylinders shows much larger coercivity than the ribbons. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1288697
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  • 2
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.369834
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  • 3
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.369962
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  • 4
    Digitale Medien
    Digitale Medien
    Two-phase high-performance Nd–Fe–B powders prepared by mechanical milling (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 1540-1544 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Nanocrystalline two-phase NdFeB+α-Fe material was prepared by milling techniques and subsequent heat treatment. These isotropic exchange-coupled powders show excellent hard magnetic properties with enhanced remanences up to 1.20 T and energy densities (BH)max around 150 kJ/m3. The performance is based on (i) the use of grain refining additions, (ii) partial substitution of Fe by Co and (iii) the use of pre-melted master alloys. The distribution of Co among the hard and soft magnetic phases upon milling and annealing is studied via Curie temperature measurements up to 10 at. % Co substitution. The effect of Co on the intrinsic properties is estimated and clarifies the extrinsic magnetic behavior. An overview of samples prepared with different milling techniques and compositions is presented. It summarizes the above listed, three different approaches to improve the magnetic performance together with the influence of the phase ratio of hard and soft magnetic phases. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1380223
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  • 5
    Digitale Medien
    Digitale Medien
    Low-noise dc superconducting quantum interference devices in Bi2Sr2CaCu2O8+x thin films (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 6703-6709 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Low-noise dc superconducting quantum interference devices (SQUIDs) were fabricated by thin film deposition of Bi2Sr2Ca Cu2O8+x (BSCCO) on bicrystalline substrates of SrTiO3 with misorientation angles aitch-theta from 24° to 45°. An optimized dc SQUID design (βL=1) was developed for aitch-theta=24°. Therein the SQUID inductance was varied between 7 and 80 pH. Fabricated dc SQUIDs operated at 77 K as well as high-quality YBa2Cu3O7−y (YBCO) SQUIDs, especially the 1/f and white noise levels were in the lowest range of data reported so far for YBCO SQUIDs and are two orders of magnitude better than noise data published this far for BSCCO SQUIDs at 77 K. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.359084
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  • 6
    Digitale Medien
    Digitale Medien
    Formation of amorphous Zr-Al-Cu-Ni with a large supercooled liquid region by mechanical alloying (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5446-5448 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Amorphous Zr65.0Al7.5Cu17.5Ni10.0 powder has been prepared by mechanical alloying from crystalline elemental powders. The powders are characterized by x-ray diffraction and differential scanning calorimetry (DSC). The amorphous phase forms after about 50 h of milling, and exhibits a wide supercooled liquid region of up to 87 K before crystallization. The transformation to the crystalline state and the melting behavior of the crystalline alloy have been followed by isothermal and constant-rate heating DSC. The results are compared with data for melt-spun and water-quenched amorphous material. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.359239
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  • 7
    Digitale Medien
    Digitale Medien
    Low-field magnetoresistance of La0.7Sr0.3MnO3 thin films with gradually changed texture (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2218-2220 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.123806
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  • 8
    Digitale Medien
    Digitale Medien
    Phase formation in mechanically alloyed Nb-Al powders (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 1399-1401 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Nb-Al alloys have been prepared by mechanical alloying of elemental crystalline powders and investigated with x-ray diffraction and transmission electron microscopy. Crystalline equilibrium phases form for Al-rich alloys. Amorphous phase formation is observed for the Nb50Al50 composition. Mechanically alloyed powders with more than 70 at. % Nb exhibit the metastable bcc (A2) solid solution which transforms after thermal annealing into the A15 phase. Formation of the different phases can be understood by considering the free-energy curves of the amorphous and bcc phases as calculated from the phase diagram and additional thermodynamic data.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.99989
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  • 9
    Digitale Medien
    Digitale Medien
    Formation of quasicrystals by mechanical alloying (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 117-119 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Quasi-crystalline Al65Cu20Mn15 powder has been produced by mechanical alloying from crystalline elemental powders. The alloying process has been monitored by x-ray diffraction, and the resulting product has been characterized by transmission electron microscopy. The quasi-crystalline phase forms after about 90 h of milling. The crystallization temperature and enthalpy have been determined by differential scanning calorimetry. The results are compared with data for melt-spun material.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.102394
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  • 10
    Digitale Medien
    Digitale Medien
    Epitaxial growth of YBa2Cu3O7−x thin films by a laser evaporation process (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 1557-1559 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Thin films of YBa2 Cu3 O7−x have been grown epitaxially in c-axis orientation on 〈100〉 SrTiO3 by pulsed excimer laser evaporation from a stoichiometric 1-2-3 target. The substrate temperature was adjusted between 720 and 780 °C, and the oxygen partial pressure during the deposition was chosen in the range 0.1–0.3 mbar. Cooled to ambient temperature in situ for 1 h in flowing oxygen gas, the films showed complete diamagnetism and zero resistance at 90 K with a transition width of 2 K. Critical current densities of 2.2×106 A/cm2 in zero magnetic field and 1.5×105 A/cm2 at 2 T were measured at 77 K. The resistivity at 100 K was about 60 μΩ cm.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.100437
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