Showing papers by "Sheldon Schultz published in 1988"
TL;DR: Superconductivity at 20 K has been unambiguously observed in the Tl-Sr-Ca-Cu-O system and this observation may provide a new insight into the mechanism of oxide superconductivity.
Abstract: Superconductivity at 20 K has been unambiguously observed in the Tl-Sr-Ca-Cu-O system. Superconductivity at 70 K was also observed in the same system. These observations may provide a new insight into the mechanism of oxide superconductivity.
73 citations
TL;DR: In this article, controlled arrays of submicron permalloy particles are used as part of a program to determine the magnetic properties of verifiable single-domain particles and the effects of interactions between SDPs.
Abstract: We have prepared controlled arrays of submicron permalloy particles as part of a program to determine the magnetic properties of verifiable single‐domain particles (SDP) and the effects of interactions between SDPs. We have measured the hysteresis loops of these arrays as a function of size, aspect ratio, and spacing. The arrays are fabricated utilizing electron beam lithography and liftoff techniques. Each array consists of approximately 106 identical particles with identical spacing between the particles. Particle size and spacing [center‐to‐center distance (ccd)], vary from 5 μm×15 μm (width by length) with ccd of 25 μm to 0.07 μm×0.1 μm with ccd of 0.25 μm. The thickness of the films varied from 0.072 to 0.049 μm. Hysteresis loops are obtained utilizing a SQUID magnetometer. For well‐separated particles we observe an order of magnitude increase in Hc with decreasing particle size, and then a subsequent decrease in Hc as the ccd is reduced. However, even for the smallest particles, the ratio of the rem...
65 citations
TL;DR: The parametrization of the measured splitting in terms of an effective Hamiltonian, the microscopic origin of the interaction within the framework of a superposition model, and the effects of the crystal-field interaction on the magnetic transition are discussed.
Abstract: We report here experimental data on the crystal-field interaction of gadolinium ions with their environment in ${\mathrm{Gd}}_{x}{\mathrm{Eu}}_{1\ensuremath{-}x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$. The ESR spectrum and a Schottky anomaly in the specific heat of dilute samples ($x\ensuremath{\ll}1$) indicate the existence of a crystal-field splitting of the $^{8}S_{\frac{7}{2}}$ ground state of ${\mathrm{Gd}}^{3+}$ ions of about 1.5 K. We discuss the parametrization of the measured splitting in terms of an effective Hamiltonian, and the microscopic origin of the interaction within the framework of a superposition model. Since the single-ion energies involved are of the same order of magnitude as the energies associated with the magnetic ordering of the ${\mathrm{Gd}}^{3+}$ moments in $\mathrm{Gd}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ (${T}_{N}\ensuremath{\cong}2.24$ K), we analyze the effects of the crystal-field interaction on the magnetic transition.
31 citations
TL;DR: The anomalous Hall coefficient of the sample itself, which is proportional to the magnetization within the sample, is used to determine the magnetisation magnetization time decay measurements made with this technique, for times>10 s, agree with vibrating-sample magnometer (VSM) data taken at 77 and 300 K, but can be made as soon as 2 ms after turning off the external magnetic field used to saturate the sample as discussed by the authors.
Abstract: We have measured magnetization time decay in perpendicularly oriented Co‐Cr films over seven time decades as a function of field and temperature The anomalous Hall coefficient of the sample itself, which is proportional to the magnetization within the sample, is used to determine the magnetization Magnetization time decay measurements made with this technique, for times>10 s, agree with vibrating‐sample magnometer (VSM) data taken at 77 and 300 K, but can be made as soon as 2 ms after turning off the external magnetic field used to saturate the sample The principle features of magnetization decay in Co‐Cr are as follows: (1) The magnetization time decay in Co‐Cr films is nearly independent of external field over a range of several kG, unlike particulate media, where the magnetization decay rate is sharply peaked around the coercive field (2) At 300 K, the magnetization time decay deviates markedly from log t, with the decay per decade of time dropping by almost a factor of 2 between 10−3 and 104 s (3
25 citations
23 citations
TL;DR: In this article, the bulk saturation magnetization, the coercive field, and the rate of magnetization decay per decade of time of IBM 3480 CrO/sub 2/ tape over the temperature range 1.6 K >
Abstract: Measurements are reported of the bulk saturation magnetization, the coercive field, and the rate of magnetization decay per decade of time of IBM 3480 CrO/sub 2/ tape over the temperature range 1.6 K >
19 citations
TL;DR: In this paper, the shape of minor loops has been measured as a function of remanence for Co-coated gamma -Fe/sub 2/O/sub 3/, barium ferrite, and iron particulate media, as well as a series of particle assemblies in which particle orientation and spacing were varied.
Abstract: The shape of minor loops has been measured as a function of remanence for Co-coated gamma -Fe/sub 2/O/sub 3/, barium ferrite, and iron particulate media, as well as a series of particle assemblies in which particle orientation and spacing were varied. The width of the loops at zero field and their axial slope were used as quantitative measures of their shape. In all cases, the minor loops for the same field extrema but different values of average remanence are not congruent. According to an operator analysis of the Preisach model by I.D. Mayergoyz (1986), noncongruence indicates that the Preisach distribution is also a function of field history. This result is in agreement with other experimental investigations of this issue. Hence, noncongruence provides a confirmation of the analysis by Mayergoyz. The amount of noncongruence is used here to determine the degree to which the Preisach distributions for various types of particle assemblies depend on field history. >
15 citations
TL;DR: The measured effective g value is shifted from the free-ion value g=1.992, indicating the existence of antiferromagnetic exchange interactions with the ions of the host.
Abstract: We have measured the electron-spin-resonance spectrum of Gd3+ ions substituting for Eu ions in Eu2CuO4. The fine structure of the spectrum was partially resolved at room temperature and the individual transitions were completely separated below 100 K. The spectrum is described with a crystal-field effective Hamiltonian of tetragonal symmetry. The values obtained at low temperatures for the corresponding parameters are b20=-486(7)×10-4 cm-1, b40=-32(2)×10-4 cm-1, and |b44|=790(50)×10-4 cm-1. These parameters are only weakly temperature dependent. The measured effective g value is shifted from the free-ion value g=1.992, indicating the existence of antiferromagnetic exchange interactions with the ions of the host. © 1988 The American Physical Society.
10 citations
TL;DR: In this article, the anomalous Hall effect voltage generated within the film itself was measured via the magnetic reversal of individual magnetic columns, which correspond to abrupt reversal of magnetic moments of from 4 x 10 −14 emu to 5 x 10−12 emu.
6 citations
TL;DR: In this article, the authors measured electron paramagnetic resonance (EPR), resistivity, and dc susceptibility from 2 to 300 K for the oxide high Tc superconductors (R)Ba2Cu3Oy (R=Y,Pr,Nd,Eu,Gd,Ho,Er,Tm, or Yb).
Abstract: We have measured electron paramagnetic resonance (EPR), resistivity, and dc susceptibility from 2 to 300 K for the oxide high Tc superconductors (R)Ba2Cu3Oy (R=Y,Pr,Nd,Eu,Gd,Ho,Er,Tm, or Yb). Selected systems were doped with 3‐d ions (Cr,Mn,Fe,Ni,Co, or Zn) or 4‐f ions (Gd or Er) which presumably substitute for the Cu or R site, respectively. In the systems studied we have observed an EPR line at low temperatures (T<40 K), which exhibits an increase in intensity and decrease in field for resonance as the temperature is lowered. The ESR linewidth is also temperature dependent and exhibits a minimum at about 15 K. An additional EPR line that can be associated with a Gd3+, Mn2+ or Er3+ ion was observed for those samples where these ions were present as dilute impurities. In some of the samples another EPR signal is observed with properties that depend on sample preparation conditions. The behavior and origin of all lines will be discussed. The variation of Tc with concentration of the added impurities over t...
2 citations
TL;DR: In this article, the decay of the magnetization with time, for a given temperature, does not follow a simple log-t relation, and the role of possible nonthermal mechanisms is discussed.
Abstract: We report on magnetization time decay (MTD) data on several commercial and experimental tapes, γ‐Fe2O3 (as a function of packing fraction), Co‐doped γ‐Fe2O3, and CrO2, measured from 2 to 400 K between 1 s and 104 s. We have found that the decay of the magnetization with time, for a given temperature, does not follow a simple log t relation. At each temperature we analyze our data with an empirical model,1 which relates values of coercive field, Hc, obtained with a 60‐Hz B‐H looper to that measured with a slow VSM field cycle (i.e., over ten orders of magnitude of time). Particular emphasis will be given to the nature of the MTD in these samples when extrapolated to zero temperature. These data will be compared to that previously reported,2 and the role of possible nonthermal mechanisms will be discussed.
TL;DR: In this article, the specific heat of Gd x Eu 1−x Ba 2 Cu 3 O 7−δ (0 ≤ × ≤ 1) was measured and the data showed a λ-type anomaly at high concentrations and a broad Schottky type anomaly at intermediate and low concentrations.
Abstract: We have measured the specific heat of Gd x Eu 1−x Ba 2 Cu 3 O 7−δ (0 ≤ × ≤ 1). The data show a λ-type anomaly at high concentrations and a broad Schottky type anomaly at intermediate and low concentrations. We compare this behavior with theoretical predictions for a 2-dimensional Ising system.