E. J. McNiff

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

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Publications (62)103.75 Total impact

  • MRS Online Proceeding Library 01/2011; 77. DOI:10.1557/PROC-77-145
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    ABSTRACT: We present a systematic study of the magnetotransport and magnetic properties of the half-doped La0.5Ca0.5MnO3+δ system. The solid is a metamagnet which undergoes a first-order antiferromagnet (AFM) to ferromagnet (FM) phase transition under a field or by changing temperature. Associated with the AFM–FM transition is an insulator to metal transition. A maximum 109-fold magnetoresistance ratio has been observed at 4.2 K between the least and the most conductive states. At low T (⩽50 K), we have also observed two additional metastable electronic states in the canted AFM state at certain fields. The resistivity of each state differs from one another by at least one order of magnitude. The existence of these multiple states may be related to the unique charge- and spin-ordered state of the half-doped manganite. © 1997 American Institute of Physics.
    Journal of Applied Physics 04/1997; 81(8):5324-5329. DOI:10.1063/1.364535 · 2.19 Impact Factor
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    ABSTRACT: Anomalous magnetic properties of organic coated NiFe2O4 nanoparticles have been reported previously (Berkowitz et al.).5 These properties included low magnetization with a large differential susceptibility at high fields and shifted hysteresis loops after field cooling, while Mössbauer spectra indicated that all of the material was magnetically ordered. In the present study, we find that the lack of saturation in high fields is accompanied by irreversibility (i.e., hysteresis loops are open) up to 160 kOe. In addition, the particles exhibit time dependent magnetization in 70 kOe applied field. The high field irreversibility and the loop shift both vanish above 50 K. We propose a model of the magnetization within these particles consisting of ferrimagnetically aligned core spins and a spin- glass-like surface layer. We find that qualitative features of this model are reproduced by a numerical calculation of the spin distribution. The implications of this model for possible macroscopic quantum tunneling in these materials are discussed. © 1997 American Institute of Physics.
    Journal of Applied Physics 04/1997; 81(8):5552-5557. DOI:10.1063/1.364659 · 2.19 Impact Factor
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    ABSTRACT: Hybrid III generated fields of 33.6 T in 1991 and 34.2 T in 1992, both in a room-temperature bore of 33 mm. Starting 1993 it has been operated as an FBNML facility magnet, generating either 33 T in a 33-mm bore or 22 T in a 144-mm bore. This paper describes our experience in operating Hybrid III over the past 8 months since December 1992. By the end of 1993, Hybrid III is expected to reach 23 T in the 144-mm bore and, with inserts employing superior alloys, 35 T in the 33-mm bore
    IEEE Transactions on Magnetics 08/1994; DOI:10.1109/20.305699 · 1.21 Impact Factor
  • L. G. Rubin, R. J. Weggel, E. J. McNiff, T. Vu
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    ABSTRACT: The high DC field facility of the FBNML marked its 30th year of operation in its present location. This year's group of users once again included more than 300 experimenters involved in ~ 100 programs. They exploited the advantages provided by the greatest number (32) and models (17) of high field DC magnets available anywhere in the world - and all at no charge. Bitter magnets with five different bore diameters provide a wide range of tradeoffs between bore size and maximum field. There are also both vertical and horizontal bore perpendicular access magnets. The operating characteristics of all these types will be presented.
    Physica B Condensed Matter 07/1994; 201:500-503. DOI:10.1016/0921-4526(94)91147-9 · 1.28 Impact Factor
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    ABSTRACT: We present an extensive study of the magnetization properties of high quality YBa2Cu3O7 and conventional low-temperature superconducting single crystals using a vibrating sample magnetometer. The experimental conditions cover a wide range of temperatures, applied fields (up to 30 T), and sweep rates. The experimentally measured linear relationship between the magnetization and the logarithm of the sweep rate is examined in detail. A simple picture of vortex motion as a combination of drift and diffusion components provides a particularly useful model for analyzing the experimental results.
    Physica B Condensed Matter 02/1994; 194:1827-1828. DOI:10.1016/0921-4526(94)91413-3 · 1.28 Impact Factor
  • Y. Iwasa, E.J. McNiff, R.H. Bellis, K. Sato
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    ABSTRACT: This paper presents magnetoresistivity data for silver used in silver-sheathed BiSCCO tapes over the temperature range 4.2 – 159 K for magnetic inductions up to 14 T.
    Cryogenics 08/1993; 33(8):836-837. DOI:10.1016/0011-2275(93)90199-X · 0.94 Impact Factor
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    ABSTRACT: The temperature dependence of the magnetic susceptibility for 1.5≪T≪300 K, the field dependence of the magnetization M(H), for 0≪H≪23 T and 1.5≪T≪15 K, and the temperature dependence of the heat capacity C(T), for 5≪T≪95 K are reported for the insulating distorted‐perovskite systems PrBaO 3 , TbBaO 3 , TbSrO 3 , and CeBaO 3 , and the pseudoternary system (Pr,Ce)BaO 3 . X‐ray analysis at room temperature indicates single‐phase structures for all materials. PrBaO 3 shows magnetic ordering below T N =11.7 K, possibly due to a canted antiferromagnetic structure. T N is nearly independent of applied field up to about 12 T. High‐field M(H) isotherms show a well‐defined upward sloping kink at 12.7 T, which is independent of temperature for T≪9.5 K. This is indicative of a spin‐reorientation transition. The pressure dependence of T N is negligible: dT N /dP≪0.1 K/kbar. TbBaO 3 and TbSrO 3 both show antiferromagnetic ordering, but with low‐ field hysteresis effects below 34 K. Clear C(T) anomalies at T N =11.7 and 34 K are seen for PrBaO 3 and TbBaO 3 , respectively. CeBaO 3 is paramagnetic, but shows no magnetic order down to 1.8 K, although M(H) is field dependent at 4.2 K. The results in the Pr‐based system are compared with previous work in high‐T c ‐related Pr‐based systems.
    Journal of Applied Physics 05/1991; DOI:10.1063/1.348209 · 2.19 Impact Factor
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    ABSTRACT: The values of critical temperatures for alloys of Pb- and SnMoâSâ were shown to be lower than those of the respective pure Chevrel phases. Chemical compositional analysis of the compounds revealed that the decreased {Tc} in the alloys are due to the off-stoichiometric compositions in the alloys. Although alloying slightly increased the values of the upper critical field H{sub c2} over that for PbMoâSâ, the H{sub c2} values for these specimens were substantially lower than those which have been reported for PbMoâSâ. Possible causes for these depressed values of H{sub c2} are discussed.
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    ABSTRACT: The values of critical temperatures for alloys of Pb- and SnMo{sub 6}S{sub 8} were shown to be lower than those of the respective pure Chevrel phases. Chemical compositional analysis of the compounds revealed that the decreased {Tc} in the alloys are due to the off-stoichiometric compositions in the alloys. Although alloying slightly increased the values of the upper critical field H{sub c2} over that for PbMo{sub 6}S{sub 8}, the H{sub c2} values for these specimens were substantially lower than those which have been reported for PbMo{sub 6}S{sub 8}. Possible causes for these depressed values of H{sub c2} are discussed.
    12/1990
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    ABSTRACT: The magnetic force which accounts for the newly-discovered suspension of a superconductor below a permanent magnet is determined by the magnetization of the superconductor and the magnetic-field gradient. Magnetization measurements were carried out on a series of YBa2Cu3Ox-AgO ceramic superconductors, with Tc~93 K. The samples were from the set of samples in which the magnetic-suspension phenomenon was first discovered. Magnetization data were taken at 4.2 and 77 K in magnetic fields up to 180 kOe. Hysteresis loops at low fields, up to 1.2 kOe, were also studied at 4.2, 77 and 87 to 88 K. The magnetization and hysteresis in most of the samples are among the largest observed to date in ceramic high-Tc superconductors. In most of our samples, the remanent moment at 4.2 K is about 80 emu/g, and about 3 emu/g at 77 K. The large magnetization and hysteresis indicate the presence of strong pinning forces. The strong hysteresis at 77 K results in an appreciable positive magnetization, parallel to the field, when the field H is decreased from a finite value (above~0.5 kOe). This positive magnetization increases with decreasing H. The positive magnetization can be produced by bringing a permanent magnet close to the superconductor, and then withdrawing it slowly. This leads to an attractive magnetic force between the superconductor and the permanent magnet. Calculations, based on a realistic model, show that at 77 K this magnetic attraction can be sufficiently strong to balance the gravitational force. As a result, the superconductor can be suspended below a permanent magnet. The expected damped oscillatory motion near the suspension point, following the application of a vertical impulse to the superconductor, is discussed. This motion is more complicated than that near the bottom of a conventional potential well. Some remaining problems associated with the magnetic-suspension phenomenon are outlined.
    Journal of Magnetism and Magnetic Materials 01/1989; 78(1):19-30. DOI:10.1016/0304-8853(89)90081-4 · 2.00 Impact Factor
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    ABSTRACT: Previously reported temperature increases above 4.2 K in an immersion geometry in liquid <sup>4</sup>He at fields ≫19 T have been verified and examined. Magnetic forces (B dB/dx) above a threshold level of ∼21 T<sup>2</sup>/cm were found to trap <sup>4</sup>He bubbles near the center of the field. Significant heat input to the region (from conduction, radiation, etc.) can then raise the temperature by as much as several kelvins. Thus, measurements at very high B dB/dx should not depend on vapor pressure thermometry. To assure temperature accuracy and stability, the temperature should be measured directly at the sample position.
    Review of Scientific Instruments 12/1988; 59(11-59):2474 - 2476. DOI:10.1063/1.1139931 · 1.58 Impact Factor
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    ABSTRACT: The authors have measured the magnetization M of superconducting YBaâCuâO/sub x/-AgO composites with T/sub c/ approximately equal to 92Î as a function of an applied magnetic field H at 77 and 87Î. A very pronounced M-H hysteresis loop occurs even at 87Î, indicating the presence of extremely strong pinning centers. The results of these measurements, together with a simple model, explain quantitatively why these superconductors could be suspended below a magnet.
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    ABSTRACT: The authors have measured the magnetization M of superconducting YBa/sub 2/Cu/sub 3/O/sub x/-AgO composites with T/sub c/ approximately equal to 92{Kappa} as a function of an applied magnetic field H at 77 and 87{Kappa}. A very pronounced M-H hysteresis loop occurs even at 87{Kappa}, indicating the presence of extremely strong pinning centers. The results of these measurements, together with a simple model, explain quantitatively why these superconductors could be suspended below a magnet.
    Modern Physics Letters B 01/1988; · 0.69 Impact Factor
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    ABSTRACT: Studies are reported of the upper critical fields of Nb0.53Ti0.47-Ge multilayers consisting of thick Ge layers and varying-thickness Nb0.53Ti0.47 layers. Both the angular dependence and the temperature dependence of the upper critical fields indicate a dimensional crossover at a Nb0.53Ti0.47 layer thickness near 200 Å. All the 2D samples display a cusplike upper critical field angular dependence with a sharper cusp for thinner Nb0.53Ti0.47 layers. The parallel upper critical fields are tentatively fitted with an expression combining the 2D field dependence of Rickayzen, the paramagnetic limiting behavior of Maki, and the disorder-related Coulomb interaction effects of Maekawa and Fukuyama. The perpendicular fields are fitted with the Maekawa, Ebisawa, and Fukuyama theory; better agreement is obtained for thinner Nb0.53Ti0.47 sublayers when the paramagnetic limiting effect is included.
    Journal of Low Temperature Physics 01/1987; 69(1):39-50. DOI:10.1007/BF00681622 · 1.04 Impact Factor
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    ABSTRACT: A dc magnetic field of 33.6±0.3 T was produced in a hybrid magnet whose central field was enhanced by a 3.5 T contribution from holmium pole pieces. The working (sample) volume was a 2‐mm gap between the 19‐mm‐diam×32‐mm‐long pole pieces tapered to 12‐mm‐diam faces. The magnetic field was measured with high‐field/low‐temperature Hall‐effect sensors whose reproducibility and linearity made practical an extrapolation technique for fields above 30 T. Three superconducting samples with previously measured upper critical fields were used as calibration check points.
    Applied Physics Letters 08/1986; DOI:10.1063/1.97080 · 3.52 Impact Factor
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    ABSTRACT: Superconductive wires containing 78 filaments of Nb 3-x Ta x Sn for 4–16 at. % Ta were produced using the external bronze process to yield a composite with an overall composition 21.4 wt. % Nb–Ta, 64.9 wt. % Cu, and 13.6 wt. % Sn. Reaction periods of 20 to 260 h at temperatures from 650 to 735 °C were used. Critical‐current densities over the entire wire cross section were 5×10<sup>4</sup> A/cm<sup>2</sup> at 14 T and 1×10<sup>4</sup> at 19.7 T, the measured H c2 was 27 T at 4.2 K for wires with 8 μm filaments containing approximately 4 at. % Ta. Single filament wires using a 13 wt. % bronze matrix were fabricated to determine the effect of Ta on reaction kinetics. The A15 layer thickness was approximately proportional to the square root of the reaction time and independent of tantalum concentration. The critical‐current densities are discussed in terms of A15 grain structure, stoichiometry, filament uniformity, and H c2 enhancement.
    Journal of Applied Physics 09/1984; 56(3-56):814 - 818. DOI:10.1063/1.334013 · 2.19 Impact Factor
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    ABSTRACT: Superconducting Cu‐Nb‐Sn multifilamentary composites are fabricated inexpensively on a laboratory scale. Small (40 μm) particles of Cu and Nb are compacted, placed in a suitable external jacket for containment, then elongated at room temperature to form a multifilamentary circular wire. Processing yields a multifilamentary Cu‐Nb‐Sn superconductor with high overall critical current densities J c at high magnetic fields. Measurements of the mechanical properties show no degradation of J c for strains greater than 1% for composite made with a large areal reduction ratio.
    Applied Physics Letters 12/1979; 35(10-35):810 - 812. DOI:10.1063/1.90945 · 3.52 Impact Factor
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    ABSTRACT: Cold‐powder‐metallurgy‐processed superconducting Cu‐Nb‐Sn (discontinuous) multifilamentary composites have been fabricated. Overall critical current J c comparable to the best in situ and commercial multifilamentary Nb 3 Sn (scaled for the same Nb content) have been achieved. Values of J c approximately 10<sup>5</sup> A/cm<sup>2</sup> at 12 T, 5×10<sup>4</sup> A/cm<sup>2</sup> at 14 T, and 2×10<sup>3</sup> A/cm<sup>2</sup> at 18 T are observed for a material with Cu–40 wt.% Nb–20 wt.% Sn with respect to Cu. The physical characteristics of the starting materials and some advantages of the cold‐powder‐metallurgy process are discussed.
    Applied Physics Letters 07/1979; DOI:10.1063/1.90665 · 3.52 Impact Factor
  • T. P. Orlando, McNiff, E. J., Jr, S. Foner, M. R. Beasley
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    ABSTRACT: The upper-critical-field behavior of Nb3Sn and V3Si is studied as a function of residual resistivity. The results are analyzed in the framework of the Ginzburg-Landau-Abrikosov-Gor'kov theory of type-II superconductivity including the effects of the electron-phonon interaction. The importance of the electron-phonon interaction on the Pauli paramagnetic limiting process is stressed and it is found that inclusion of the electron-phonon corrections (most importantly the electron-phonon renormalization of the normal-state parameters) is needed to sensibly fit the data. For Nb3Sn failure to include these effects leads to too high spin-orbit scattering rates. The critical-field data are also used to determine the density of states of these materials as well as several other superconducting and normal-state parameters.
    Physical Review B 05/1979; 19(9):4545-4561. DOI:10.1103/PhysRevB.19.4545 · 3.74 Impact Factor