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  • 1
    Electronic Resource
    Electronic Resource
    Observations of magnetization reversal and magnetic clusters in copper ferrite films : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6822-6824 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The observation of a magnetization reversal and a superparamagnetic behavior are reported for films of copper ferrite sputtered in an oxygen atmosphere. X-ray diffraction studies indicate the presence of 14-nm nanoscale crystals of CuFe2O4 in the films. Data on the temperature dependence of the film magnetization M for zero-field-cooled (ZFC) and field-cooled (FC) show that ZFC and FC curves separate at a temperature Tf and that Tf decreases with increasing static field strength. For T〈Tf, M vs T data for low fields indicate the presence of a compensation point in virgin samples. For T(approximately-greater-than)Tf, a superparamagnetic character is evident form the high-field magnetization data. An average cluster size of 16 nm obtained from such data is in excellent agreement with the results of x-ray diffraction studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356819
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic and magnetoresistance studies on radio frequency sputtered La–Pb–Mn–O films : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5185-5187 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results on structural and magnetic characterization of radio frequency sputtered thin films of La0.74Pb0.26MnOz on (100) Si are presented. Stoichiometric films with a thickness of 0.6 μm showing (110) textured growth were deposited in a mixed argon–oxygen atmosphere. The low temperature magnetization is 10% smaller than the expected value for a collinear ferromagnetic order in the oxide. Zero-field resistivity data show a metal-to-semiconductor transition centered at Tms=250 K. Data on magnetoresistance (MR)=[ρ(0)−ρ(H)]/ρ(0) versus temperature reveal the following important features: (i) a maximum value of 22% for H=2 T at the metal-to-insulator transition temperature, (ii) MR value of 15%–22% over the entire temperature range 4.2–300 K, and (iii) a substantial MR, ∼10% even at temperatures as high as 380 K, well above the Curie temperature. Data on the temperature dependence of ferromagnetic resonance linewidth at 9.4 GHz show a discontinuity at Tms. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361333
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetism and spin dynamics of nanoscale FeOOH particles : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5873-5875 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nature of magnetism and electron paramagnetic resonance (EPR) spin dynamics in 30 A(ring) particles of FeOOH have been investigated in the range 5–350 K. X-ray diffraction shows that the particles are neither α-Fe2O3 nor α-FeOOH based and they convert to Fe3O4 (α-Fe2O3) on heating to 800 K in vacuum (air). Magnetization M vs T data show a blocking temperature TB in the range 40 K〈TB〈100 K so that for T≥100 K, scaling of M with H/T for H up to 50 kOe verifies superparamagnetism. In EPR, both the linewidth ΔH and the g value decreases upon increasing T so that near 300 K, g(approximately-equal-to)2.05 (characteristic of Fe3+). A model of motional narrowing is used to explain the ΔH vs T behavior. The dramatic changes in M, ΔH, g value, and the recoilless fraction of Mössbauer spectroscopy observed near 50 K are all related to the thermal motion of the superparamagnetic nanoscale particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355545
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic properties of amorphous BiFeO3-PbZrO3 sputtered films : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5463-5465 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous thin films of (1−x)BiFeO3-xPbZrO3 for x=0.1–0.9 have been prepared by the technique of rf sputtering and the effects of sputtering conditions and annealing at high temperatures on magnetic properties of such films have been studied through magnetization measurements. A sintered polycrystalline target was used to sputter 0.2–1.4-μm-thick films in oxygen, argon, and mixed oxygen and argon atmospheres onto glass and silicon substrates. As-sputtered films are x-ray amorphous and show paramagnetism at room temperature. A hard-ferromagnetlike character with remanence is observed in films annealed at temperatures Ta above 500 °C. The room-temperature magnetization increases with further increase in Ta and shows a maximum for Ta = 650 °C. A partial crystallization occurs for Ta (approximately-greater-than) 650 °C and is accompanied by a decrease in the magnetization. The magnetization for annealed samples shows a dependence on x, with a minimum of 0.6 emu/g for x=0.9 and a maximum of 40 emu/g for x=0.5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348010
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  • 5
    Electronic Resource
    Electronic Resource
    Magnetic properties of radio frequency sputtered thin films of La–Pb–Mn oxides (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2090-2092 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the synthesis by radio frequency sputtering and characterization of thin films of La0.74Pb0.26MnOz on Si, the substrate of choice for device integration. Textured films with (110) orientation were grown on (100) Si and the films are ferromagnetic below 325 K. Resistivity ρ data show a metal-to-semiconductor transition at Tms=250 K. The ferromagnetic resonance linewidth shows a discontinuity at Tms. Data on magnetoresistance MR=[ρ(0)−ρ(H)]/ρ(0) versus temperature indicate a maximum value of 22% at Tms for a static magnetic field of 2 T and MR values of 15%–22% are observed over the entire temperature range 5–300 K. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115088
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  • 6
    Electronic Resource
    Electronic Resource
    Mössbauer and magnetic-susceptibility studies on MmNi4.15Fe0.85 and its hydride (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5873-5875 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results are reported on MmNi5−xFex (x=0.85) (Mm=mischmetal) and its hydride from magnetic susceptibility (χ), Mössbauer, and scanning-electron-microscopy studies. The magnitude of χ, the shape of the χ-vs-T curve (50–300 K), and the magnitude of Tc ((approximately-equal-to)200 K) are all close to the values reported for LaNi4Fe. The magnetic properties are significantly changed by the hydriding process. χ (at 100 Oe) above Tc is increased by 100%, whereas at 77 K, χ is lowered by 25%, although Tc is unaffected. The Mössbauer spectra above Tc yield a paramagnetic doublet (isomer shift −0.13±0.01 mm s−1); however, as the temperature decreases, the doublet disappears at 125 K. Hydriding causes only a very small change in the isomer shift.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345999
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  • 7
    Electronic Resource
    Electronic Resource
    Antiferromagnetic states in CopMg1−pO (abstract) (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5990-5990 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: CopMg1−pO offers an excellent prototypical example for the study of antiferromagnetism in diluted fcc lattices. The system retains the same crystallographic structure (NaCl type) over the entire 0≤p≤1 range. The Co2+ ions form a randomly diluted fcc spin lattice with predominantly next-nearest-neighbor antiferromagnetic (AF) exchange coupling. No significant changes in J are expected with magnetic dilution, since the lattice parameter changes only slightly (∼1%) between p=1 and p=0. The χ(p,T) data1 for the system reveal a distinct crossover effect at p≈0.45. A similar behavior of the χ(p,T) curve was observed in an isostructural system EupSr1−pTe, and was interpreted as an AF→SG (SG=spin glass) transition.2 Recently, we have reported low-T neutron-diffraction data3 from CopMg1−pO samples with various p, showing a breakdown of the type-II AF long-range order (LRO) in the system at p≈0.47. In this paper we present the results of measurements of the temperature dependence of magnetic peak intensities and widths which provide a further evidence for a sharp LRO-SRO (short-range order) phase boundary in the system. However, neutron-diffraction data alone cannot answer the question of whether the SRO phase is a SG state. In order to obtain a closer understanding of the LRO-SRO transition in type-II antiferromagnets, we have carried out Monte Carlo simulations on diluted fcc spin arrays. Since CopMg1−pO is an Ising-like system (due to significant crystal-field anisotropy), and some other materials of current interest (e.g., EupSr1−pTe) are Heisenberg systems, we discuss this question in context of simulation data obtained from both Heisenberg and Ising spin arrays.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346039
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  • 8
    Electronic Resource
    Electronic Resource
    Evidence of clustering of magnetic ions in weakly doped MgO crystals (abstract) (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5990-5990 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature dependence of the magnetic susceptibility of CopMg1−pO and MnpMg1−pO systems has been measured in the temperature range of 1.7–300 K. The nominal compositions investigated are p=0.000 84 and 0.0048 for the MnpMg1−pO system, and p=0.000 31, 0.0099, 0.07, and 0.10 for CopMg1−pO. The data are analyzed in terms of contributions from the single ions (Mn2+ and Co2+) and the exchange-coupled pairs (dimers). For the MnpMg1−pO system, it is found that concentration of dimers determined from a theoretical fit to the data is nearly an order of magnitude larger than that expected from the random distribution of Mn2+ ions, suggesting clustering of the Mn2+ ions in MgO [B. L. Gordon and M. S. Seehra, Phys. Rev. B 40, 2348 (1989)]. For the CopMg1−pO system, the analysis is complicated by the effect of spin-orbit interaction and leads to a fictiously large ((approximately-equal-to)50 K) Curie–Weiss temperature even for the p=0.000 31 sample, in agreement with the experiment. Analysis of the data by including the effect of exchange interaction is now underway, and these results will be reported elsewhere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346038
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  • 9
    Electronic Resource
    Electronic Resource
    Potassium perchromate standard for determination of paramagnetic spin concentration, g values, and magnetic moments of fossil fuels (1981)
    s.l. : American Chemical Society
    Analytical chemistry 53 (1981), S. 938-940 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac00229a056
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  • 10
    Electronic Resource
    Electronic Resource
    Magneto-transport properties of Bi substituted thin films of La–Ca–Mn–O (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 667-669 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This letter is on the observation of anisotropic electrical transport and magnetoresistance (MR) in rf sputtered thin films of La0.62Bi0.05Ca0.33MnO3 on Si. Films sputtered on (111)Si are polycrystalline, whereas textured films with (110) orientation are obtained from (100) Si. Both films show a reduction in the lattice constant and relatively high Curie temperatures (262–266 K vs 230 K for bulk polycrystals). Although the films have identical magnetic parameters, resistivity ρ and MR data for the (110) textured films show the following features indicative of possible dependence of magneto transport on crystallographic orientation: (i) a two order of magnitude enhancement in the low temperature ρ value compared to polycrystalline films, (ii) a semiconductorlike electrical conduction and the absence of any metallic to semiconductor transition, and (iii) a relatively large MR, as high as 80% at 40 kOe. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118328
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