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  • 1
    Electronic Resource
    Electronic Resource
    Magnetic properties of monodomain Nd-Fe-B-C nanoparticles : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5293-5295 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nanoparticles of Nd-Fe-B-C with their crystal structure similar to the Nd2Fe14B phase were generated in a carbon arc. With an average diameter of less than 40 nm, they are monodomain. They have a smaller room-temperature coercivity than would be predicted from the bulk magnetocrystalline anisotropy. However, their coercivity is greater than was previously observed in particles 〈5 μm prepared by spark erosion. While the carbon arc process is useful for making small carbon-coated particles which resist oxidation, here dispersion of excess Nd in the carbon matrix results in a significant paramagnetic signal. The dc demagnetization curves enable the paramagnetic and ferromagnetic contributions to be distinguished. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361355
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  • 2
    Electronic Resource
    Electronic Resource
    Calculation of magnetic moments in Ho2C3 nanocrystals : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6307-6309 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A general approach to the computation of effective magnetic moments in rare-earth carbides is described, and details of this calculation for Ho3+ ions in Ho2C3 are presented. This calculation is designed to explain the reduced magnetic moments, relative to free ion values, measured by dc SQUID magnetometry for Ho2C3 nanocrystals. Crystal-field splittings of the rare-earth ion in a particular symmetry site are determined by the operator equivalent method. Using the eigenvalues and eigenfunctions of the crystal-field Hamiltonian, the effective magnetic moment is then determined. For Ho3+ ions in Ho2C3, this method predicts a reduced magnetic moment, but the degree of reduction depends on the energy-level splittings and, therefore, the temperature. This magnetic moment is compared with previous experimental results, and the implications of the formal carbon charge, screening, and temperature are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358535
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic properties of carbon-coated rare-earth carbide nanocrystallites produced by a carbon arc method : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5879-5881 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Carbon-coated gadolinum and holmium carbide nanocrystallites have been generated using a modification of the Huffman-Krätschmer carbon arc process. Bulk amounts of these particles were isolated from the other by-products using a magnetic field gradient. Transmission electron microscopy revealed the presence of 10–50 nm diameter crystallites coated with numerous graphitic layers. The nanocrystallite phases were identified as Gd2C3 and Ho2C3, respectively, by x-ray and electron diffraction. Magnetization measurements were performed using a superconducting quantum interference device magnetometer between ±5 T at temperatures ranging from 4 to 200 K. The magnetization curves were shown to scale as a function of H/T. The RE3+ sites in RE2C3 have C3 site symmetry. For Gd2C3 the universal curve was fit with a Brillouin function consistent with the Gd3+ free-ion ground-state values of J=7/2 and g=2. The 5I8 Ho3+ free-ion ground state is split, presumably due to a C3 symmetry crystal field. Consequently, for Ho2C3 the Ho3+ free-ion parameters could not be used to fit the experimental data. Empirical fits to the Brillouin function yield a reduced moment of 7.5μB, compared to the free-ion value of 10.6μB. A similarly reduced moment was observed in holmium-containing endohedral fullerenes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355547
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic properties of carbon-coated, ferromagnetic nanoparticles produced by a carbon-arc method : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5882-5884 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Krätschmer–Huffman carbon-arc method of preparing fullerenes has been used to generate carbon-coated transition metal (TM) and TM-carbide nanocrystallites. The magnetic nanocrystallites were extracted from the soot with a magnetic gradient field technique. For TM=Co the majority of nanocrystals exist as nominally spherical particles, 0.5–5 nm in radius. Hysteretic and temperature-dependent magnetic response, in randomly and magnetically aligned powder samples frozen in epoxy, correspond to fine particle magnetism associated with monodomain TM particles. The magnetization exhibits a unique functional dependence on H/T, and hysteresis below a blocking temperature TB. Below TB, the temperature dependence of the coercivity can be expressed as Hc=Hc0[1−(T/TB)1/2], where Hc0 is the 0 K coercivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355548
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  • 5
    Electronic Resource
    Electronic Resource
    Monolayer magnetism of 3d transition metals in Ag, Au, Pd, and Pt hosts: Systematics of local moment variation : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5932-5934 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electronic and magnetic properties of T/Aun, T/Agn (T=Cr, Mn, Fe, Co, and Ni), Fe/Pdn and Fe/Ptn multilayers and sandwiches have been computed using the layer Korringa–Kohn–Rostoker (LKKR) band-structure technique. Enhanced (as compared with bulk) 2D T magnetism is observed in all Cr, Mn, and Fe/host configurations, consistent with weak coupling between Cr, Mn, and Fe d bands and those of the noble metal (NM) hosts and consequently d bandwidths which are exceeded by the exchange splitting. Fe and Cr moments vary systematically with the number of mediating Ag or Au planes and the Fermi energy of the system. These systematics are explained by considering the variation of the Fermi energy (EF) with composition as well as constraints of charge neutrality and strong (single-band) ferromagnetism. For Fe in Pt and Pd hosts, d-d hybridization leads to a nearly invariant Fe moment as a function of the number of mediating Pd or Pt planes but with large induced moments on the host.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350109
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  • 6
    Electronic Resource
    Electronic Resource
    Time-dependent response and the de Almeida–Thouless line in R 1:2:3 superconductors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5058-5060 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: As shown recently, the time-dependent response in high-temperature superconductors can be well evaluated on the basis of the classical theory of first-order relaxation processes, if the temperature is low enough. In this article we extend our investigation to the high-temperature limit and show that the decrease of the logarithmic relaxation rate is an experimental consequence of the relaxation model and not a critical slowing down. On the basis of a comparison of the different classical relaxation processes and superconductive time-dependent response the special features of the superconductor can be interpreted. It is shown that all irreversible relaxation results in thermal hysteresis as a consequence of the difference between the time scale of the relaxation and the experiment. This feature introduces difficulties into the experimental determination of the de Almeida–Thouless lines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344669
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  • 7
    Electronic Resource
    Electronic Resource
    Properties of rapidly quenched Ti(Ni,Fe)Si alloys (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5885-5887 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Alloys of the series Ti56Ni28−xFexSi16 (x=0,...,20) can be prepared either in the amorphous phase or as single phase quasicrystals by rapid solidification. Here electrical resistivity and magnetic susceptibility measurements are reported. All amorphous alloys and quasicrystalline samples with x≥10 reveal Curie-like magnetic susceptibility and electrical resistivity dominated by structural scattering. The quasicrystalline samples with x〈10 demonstrate nonCurie susceptibility and a minimum in ρ(T) where Tmin varies inversely with Fe content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346003
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of Fe on the ferromagnetic properties of Al-Mn-based quasicrystals (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5879-5881 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization and Mössbauer-effect studies of ferromagnetic Al-Mn-Si and Al-Mn-Cu-Ge quasicrystals are presented. All alloys show paramagnetic or spin-glass behavior in addition to ferromagnetism at low temperatures. The effects of Fe substitution on the magnetic properties were investigated. Possible models for ferromagnetic order in quasicrystals are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346001
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  • 9
    Electronic Resource
    Electronic Resource
    Melting and solidification behavior of YBa2Cu3O7−x (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3662-3666 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have prepared the superconducting compound YBa2Cu3O7−x through a melt process. Solidification of this material at cooling rates 〈105 K/s yields BaCuO2 and a previously unreported metastable phase which indexes to a cubic pattern with a lattice constant of 0.701 nm. Faster solidification rates yield only the cubic phase and glassy materials. Annealing these materials in O2 gives rise to a single-phase material of the YBa2Cu3O7−x orthorhombic structure. The material has zero resistance at 91.6 K with a transition width of 1.4 K. The grain size of the materials after annealing averages 10 μm in length and 2–3 μm in width, and the grains are compositionally homogeneous. Twins are seen with spacings on the order of 20 nm. The irreversibility of the magnetization curve at low temperatures can be ascribed to strong flux pinning mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342591
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetic properties and microstructural observations of oxide coated FeCo nanocrystals before and after compaction (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4406-4408 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A radio frequency (rf) plasma torch has been used to produce FeCo nanoparticles with a thin protective oxide coating from metal powder precursors. Structural characterization by conventional and synchrotron x-ray diffraction indicated a disordered bcc α-FeCo phase. High resolution transmission electron microscopy revealed spherical particles with several monolayer thick protective oxide coatings. Thermomagnetic measurements were carried out using a superconducting quantum interference device magnetometer and a vibrating sample magnetometer at temperatures between 5 and 1050 K. Antiferromagnetic (exchange bias) coupling was observed due to the presence of the oxide layer. Relatively high coercivities were observed (280 Oe at 5 K and 250 Oe at room temperature). Néel's surface (interface) anisotropy model was employed to explain the origin of the observed coercivities. As produced powders were hot isostatically pressed at 1023 K and 22 ksi for 2 h. Dense structures were observed and compacted particles revealed coercivities as low as 25 Oe at room temperature. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369799
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