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  • American Institute of Physics (AIP)  (48)
  • 1
    Electronic Resource
    Electronic Resource
    Magnetism and epitaxy in Lu/Dy/Lu trilayers : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6901-6903 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin dysprosium c-axis films (40–400 A(ring)) were grown coherently between 500-A(ring) lutetium layers by molecular beam epitaxy. Bulk magnetization measurements show that these sandwich structures order magnetically at TN(approximately-equal-to)178 K (=TN of elemental Dy) and undergo ferromagnetic transitions at temperatures which range from 100 K (400 A(ring) Dy) to 175 K (40 A(ring) Dy), significantly enhanced from the bulk TC=85 K. The Dy basal plane lattice parameters in the films were determined by room-temperature x-ray diffraction. We observe a change in these values that correlates with the rise in TC, which suggests that this rise is due to epitaxial strain. The relatively small low-temperature magnetic susceptibility displayed by these samples indicates the presence of a large anisotropy in the basal plane. We address both the issues of the susceptibility and the high ferromagnetic transition temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352428
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  • 2
    Electronic Resource
    Electronic Resource
    Two-dimensional modulated ferrimagnetic systems (abstract) : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4903-4903 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bi2Sr2MnOy, isomorphic to the high-Tc compound containing Cu, exhibits a displacement modulation driven by the bending of Bi double layers, thus creating a modulated environment for the magnetic MnO2 layers which are 12 A(ring) apart. Neutron scattering results will be presented, showing antiferromagnetic order in zero field and a field-induced transition to weak ferromagnetism. This behavior is a direct consequence of the structural modulation which breaks the symmetry of two otherwise equivalent ordering directions of (010) and (100)−the latter being associated with weak ferromagnetism. Magnetic scattering has been observed at superlattice positions, suggesting that the displacement modulation affects the valence of the magnetic ions. Subtle differences in magnetic behavior are observed in similar compounds where Pb is substituted for Bi and Ca for Sr. These results will be discussed in terms of a modulated magnetic model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348950
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  • 3
    Electronic Resource
    Electronic Resource
    Inelastic neutron scattering studies of II-VI diluted magnetic semiconductors (invited) (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5096-5101 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Inelastic neutron scattering studies of AII1−xMxBVI diluted magnetic semiconductor (DMS) alloys with low and high concentations of the magnetic component (M) are reviewed. Measurements of inelastic scattering from isolated pairs of magnetic ions makes possible a direct determination of the ion–ion exchange parameters. This method has been used for JNN determination in Zn1−xMnxB (B=S, Se, Te) and Zn1−xCoxB DMS alloy families. Inelastic scattering experiments on DMS alloys with high magnetic ion concentrations (Zn1−xMnxTe and Cd1−xMnxTe with x=0.4–0.7) reveal that at low T the magnetic excitation spectra of these systems are dominated by magnonlike modes despite the absence of long-range magnetic order. A theoretical description of these excitations can be obtained using the numerical method developed by Ching and Huber. The model results reproduce remarkably well the dispersion and the line-shape characteristics of the excitation modes seen in the experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344683
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic excitations in thulium metal (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5283-5285 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed inelastic neutron scattering measurements on a single-crystal specimen of Tm at wave vectors κ=(1, 1,ζ) and (0,0,2+ζ) (ζ=0,...,1). Most of the measurements have been made at T=5 K, where Tm exhibits a seven-layer ferrimagnetic-antiphase-domain structure (four moments up, parallel to the c axis, followed by three moments down). At this temperature the excitation spectra consist of three peaks. The two lower energy excitations have been identified as originating from magnetovibrational scattering from the TA phonon, while the higher energy excitation is magnetic and exhibits only a weak dispersion (between 8.3 and 9.6 meV). At T=50 K, a temperature at which the system exhibits a c-axis sinusoidally modulated structure, the magnetic mode shows significant softening and broadening. The magnetovibrational scattering vanishes above the Néel temperature (TN=58.5 K) while the magnetic mode persists at least up to T=70 K. These results suggest that the Hamiltonian in this system is dominated by the crystal-field-anisotropy energy and that the exchange interaction is relatively weak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344637
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  • 5
    Electronic Resource
    Electronic Resource
    Spin dynamics of amorphous Fe90−xNixZr10 (invited) (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5223-5228 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous Fe90−xNixZr10 is a system that exhibits a relatively high degree of magnetic exchange frustration, which becomes stronger as the system approaches the composition of amorphous pure iron. Thus, while samples with moderate amounts of iron (x≥5) are ferromagnetic, the samples with the highest concentration of iron (x≤1) behave like reentrant spin glasses. We have performed a detailed neutron scattering study of the spin-wave excitations in this system for x=1, 5, 10, 20. In all cases, well-defined spin-wave excitations were observed below a transition temperature Tc that decreased from 455 K (for x=20) to 250 K (for x=1). For x=5, 10, 20 the spin-wave stiffness coefficient follows the temperature dependence expected for a conventional ferromagnet but the spin-wave excitations broaden considerably at low temperatures. For x=1 the spin-wave stiffness coefficient softens at low temperatures and an elastic component of the scattering, associated with the development of a spin-glass order parameter, appears below T≈0.28Tc. A coexistence of propagating spin-wave excitations and spin freezing phenomena is observed below this temperature down to T=0.09Tc. These results are discussed in terms of the relevant current theories.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344618
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetic structure in Dy/Sc superlattices : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6904-6906 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated magnetic order in superlattices of Dy and Sc grown along the hcp c axis by molecular beam epitaxy (MBE) techniques. Our neutron diffraction experiments reveal that individual Dy layers order ferromagnetically below Tc∼150 K. The magnetic coherence length along the growth direction is less than the Dy-layer thickness. Previous studies of rare-earth superlattices with Y or Lu as spacer layers have shown that magnetic coherence propagates through sufficiently thin nonmagnetic interlayers. This arises from the long-range exchange interaction that originates from nesting features in the Fermi surface of the spacer material. The lack of coupling in Dy/Sc superlattices reflects the very different Fermi surface of Sc, with much weaker nesting than Y and Lu.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352429
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  • 7
    Electronic Resource
    Electronic Resource
    Antiferromagnetism in epilayers and superlattices containing zinc-blende MnSe and MnTe : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6221-6223 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: New zinc-blende Mn-based magnetic semiconductors offer unique insights into the magnetic order and critical behavior of frustrated antiferromagnets. Molecular beam epitaxy grown samples exist both in the form of strained superlattices, with strain induced anisotropies (MnSe/ZnSe and MnTe/ZnTe), and in the form of near-isotropic bulk MnTe. The tetragonally distorted strained superlattices exhibit a second-order phase transition, consistent with symmetry arguments favoring such behavior. In contrast, the bulk-like epitaxial layers of MnTe have a first-order phase transition, associated with magnetostriction, unknown to an unaccounted for by the previous studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350001
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of epitaxial strain in Er/Lu thin films : 35th annual conference on magetism and magnetic materials San Diego, California (USA) 29 Oct−1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4535-4537 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of c-axis Er films ranging in thickness from 400 to 9500 A(ring) were grown on lutetium base layers to investigate the effects of epitaxial growth on the magnetic properties of bulk erbium. Neutron diffraction studies show that the basal plane lattice parameter of Er approaches the smaller Lu value as the films are made thinner. Below TN the phase angles of the Er spin modulation are diminished from bulk Er values in the thinner films. For all but two 800-A(ring) films, there is evidence from bulk magnetization and neutron data of a first-order transition to a conical ferromagnetic state, similar to bulk Er. These phenomena are compared to the properties of Er films grown on yttrium, whose basal plane spacing exceeds that of Er. In these systems the turn angles are greater than bulk and the ferromagnetic phase is suppressed. This contrasting behavior is consistent with predictions from a magnetoelastic energy model of epitaxial constraint developed to describe the Er/Y systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348351
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  • 9
    Electronic Resource
    Electronic Resource
    Antiferromagnetic ordering in MnSe/ZnSe multilayers : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6109-6111 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report neutron diffraction studies of zinc-blende strained MnSe/ZnSe superlattices. Such systems are examples of a fcc Heisenberg antiferromagnet of the third kind. The results show clearly long-range order in the MnSe layer plane, and no magnetic coupling across the passive layers. The strain affects the relative domain population. Measurements of the diffracted intensity versus T show that the AF phase transition in the MnSe layers is of second order with TM = 107 ± 5 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347782
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  • 10
    Electronic Resource
    Electronic Resource
    Small-angle neutron scattering from bacterial magnetite (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4475-4477 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Small-angle neutron scattering was used to study the magnetic properties of intracellular magnetite crystals (magnetosomes) in the bacterium, Aquaspirillum magnetotacticum, grown in pure culture. An average of 20 single-domain magnetite (Fe3O4) particles of diameter 400–500 A(ring) are arranged in a chain that longitudinally traverses each cell. The net magnetic dipole moment carried by each chain is sufficient to orient the bacterium in the geomagnetic field. A contrast variation series, performed on a nonmagnetic variant, established that a 30% D2O/H2O ratio in the suspension buffer resulted in the minimization of the scattering from the bacterium itself, thereby enhancing that from the magnetosomes. Measurements of A. magnetotacticum in 30% D2O and an applied field of 25 G confirmed that the scattering from the magnetite particles in bacteria grown under iron-rich conditions is of ferromagnetic character, while that from magnetosomes in bacteria grown under iron-starved conditions is characteristic of superparamagnetic particles. In both cases, the wave-vector dependence of the scattering can be represented by a sum of Lorentzian plus Lorentzian squared terms, from which longitudinal as well as transverse spin correlation lengths were extracted. The results describe dynamic spin correlation lengths on the order of 50 A(ring), which are superposed on the static magnetosome cluster.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344886
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