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  • 1
    Electronic Resource
    Electronic Resource
    A neutron scattering study of the quasi-one-dimensional, dilute Ising-like antiferromagnet CsCo0.83Mg0.17Br3 : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6451-6453 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutron scattering measurements have been performed on a single-crystal sample of CsCo0.83Mg0.17Br3, a quasi-one-dimensional, Ising-like antiferromagnet. Residual three- dimensional interactions between the dilute magnetic chains precipitate a phase transition to long-range order at TN∼9.0 K, and short-range correlations persist as high as 40 K. Relatively high-energy inelastic scattering from both "bulk'' spin-wave modes and "end'' modes is observed from the finite chains. The low-energy inelastic spectrum is dominated by soliton scattering due to antiphase domain walls propagating along the finite chains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352630
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  • 2
    Electronic Resource
    Electronic Resource
    Search for the breakdown of the spin-wave approximation in EuO (abstract) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7023-7023 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spin-wave approximation in a Heisenberg ferromagnet is valid at low temperatures where the spin-wave interactions are negligible. At higher temperatures these interactions become highly nonlinear and the spin-wave approximation should break down. In a recent paper Fishman and Vignale1 predicted that this breakdown should occur near the temperature T¯=0.4zJs, where z is the number of nearest neighbors, J is the ferromagnetic coupling constant, and s is the spin of the ferromagnet. In another related paper Fishman and Liu2 have calculated that above this temperature T¯ a second pole appears in the correlation function at an energy close to 2zJs. The origin of this new mode is the strong coupling of transverse and longitudinal fluctuations that forces the spins to precess about their local mean field. When the "spin-wave'' energies are close to the precessional mode energy 2zJs a splitting of the "spin-wave'' branch is predicted. In order to test this prediction we have performed a high-resolution inelastic neutron scattering experiment to measure the spin waves in EuO, a prototypical Heisenberg ferromagnet, in the vicinity of the q-E region where this splitting should occur. Although our experiment was performed at T=20 K, which is above T¯≈12 K, our measurements failed to observe the predicted splitting of the "spin-wave'' branch. Only a single resolution-limited spin-wave branch was observed, in agreement with earlier measurements by Passell et al.3
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354050
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Small-angle neutron-scattering studies of Ce(Fe1−xAlx)2 : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6066-6068 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ce(Fe1−xAlx)2, with x=0, 0.06, and 0.14, has been studied by small-angle neutron scattering in order to investigate the instability of the ferromagnetic state in the pure material to small amounts of magnetic disorder. The pure material (x=0) displays a ferromagnetic transition near TC=225 K, and more complicated behavior below ∼100 K. The disordered alloys, x=0.06 and x=0.14, display ferromagnetic-like states over relatively narrow temperature ranges, and an additional low-temperature phase. The ferromagnetic-like state in the x=0.14 alloy appears to be qualitatively different from that exhibited by the other two. High-wave-vector-resolution measurements on the x=0.06 sample indicate that its low-temperature ordered phase is ferrimagnetic in origin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353471
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  • 5
    Electronic Resource
    Electronic Resource
    High-energy magnetic excitations in Mn90Cu10 : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6548-6550 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The study of the magnetic excitations in Mn-rich alloys should be a good test of the multiband calculations of the spin dynamics of pure γ-Mn, which is a prototypical itinerant-electron antiferromagnet. In this paper we report the results of recent neutron inelastic scattering measurements performed on Mn90Cu10 at room temperature (T=0.63TN) and up to 300 meV of energy transfer. These measurements were performed using the high-energy transfer (HET) chopper spectrometer at the ISIS spallation neutron source, Rutherford Appleton Laboratory, U.K. The results are in agreement with calculations using a model scattering function convoluted with the full HET resolution function. In this model there is a steep linear spin-wave dispersion (D≈250 meV A(ring)) for wave vectors up to ≈1/2 of the Brillouin zone and a strong damping which is linear in the wave vector q. For larger wave vectors the spin-wave energies are constant at about 190 meV. These features are qualitatively similar to the predictions of Cade and Young for pure γ-Mn.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352559
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Spin dynamics in a diluted Heisenberg NN antiferromagnet on a HCP lattice: Zn1−xMnxSe (abstract) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5660-5660 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nature of magnetic excitations in disordered and short-range ordered antiferromagnetic systems continues to be an interesting problem. The family of AII1−xMnxBVI alloys (AII=Zn, Cd, Hg, BVI=S, Se, Te) offers highly interesting prototypes for such studies. In these systems, which crystallize in the zinc blende (ZB) or wurtzite structure, the Mn ions form, respectively, diluted FCC or HCP Heisenberg spin lattices with dominating nearest-neighbor AF coupling. Due to the strong frustration inherent in such lattices these systems do not exhibit long-range spin order even for Mn concentrations as high as x=0.70. Neutron scattering studies of spin dynamics in the zinc-blende forms (Zn1−xMnxTe and Cd1−xMnxTe) have been reported in a recent article.1 In the present paper we report the results of experiments on a wurtzite-type system, Zn1−xMnxSe, with x=0.55 and 0.40. As in the previous case of ZB alloys, the data reveal the existence of magnon-like modes that are extremely strongly damped, but still show a pronounced dispersive behavior. The range of static AF spin–spin correlations in Zn1−xMnxSe is extremely short (ξ=κ−1=5–15 A(ring)), and exhibits a significant anisotropy. The energy of the observed excitation is clearly correlated with ξ, i.e., it is higher in the Q-space directions for which the correlation range is longer. The results are discussed in the context of the existing theoretical models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353634
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  • 8
    Electronic Resource
    Electronic Resource
    Neutron diffraction study of the magnetic structures of CeMn2Ge2 and CeMn2Si2 : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5398-5400 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed high-resolution neutron powder diffraction measurements on CeMn2Si2 and CeMn2Ge2 at temperatures between 12 and 550 K. Our measurements indicate that at high temperatures both compounds are paramagnetic. Below TN=380 K CeMn2Si2 becomes a collinear AF, with a structure similar to that reported by Siek et al. in which the magnetic propagation vector is τ=(0 0 1). CeMn2Ge2, on the other hand, exhibits two different magnetic transitions. At TN≈415 K there is a transition to a collinear AF phase characterized by the commensurate propagation wave vector τ=(1 0 1). At TC≈318 K there is a transition to a conical structure with a ferromagnetic component along the c axis and a helical component in the ab plane. The helical component is characterized by the incommensurate propagation vector τ=(1 0 1−qz), where qz is temperature dependent. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362317
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  • 9
    Electronic Resource
    Electronic Resource
    Neutron diffraction study of the magnetic ordering of BaCuO2+x (abstract) : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6603-6603 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutron diffraction experiments have been performed in order to study the magnetic ordering of BaCuO2+x. In these measurements unpolarized neutrons and polarized neutrons with full polarization analysis have been utilized. From these measurements it has been determined that BaCuO2+x orders antiferromagnetically below TN=15.0±0.5 K with a magnetic propagating vector κ=[1 1 1]. This structure is commonly referred to as a [πππ] or a G structure. The Cu atoms in the Cu6 ring clusters, located at the (1/4, 1/4, 1/4) positions, order ferromagnetically within these clusters while the clusters themselves order antiferromagnetically. The ordered magnetic moment of each of these Cu atoms is 0.89±0.05 μB at T=4.2 K. No evidence of long-range magnetic ordering of the Cu atoms in the Cu18 clusters, located at the (0, 0, 0) and (1/2, 1/2, 1/2) positions, was found down to a temperature T=2.5 K. The work at Oak Ridge National Laboratory (ORNL) was sponsored by the Division of Materials Sciences, U.S. Department of Energy (DOE). ORNL is managed for the U.S. DOE by Martin Marietta Energy Systems, Inc., under Contract No. DE-AC05-84OR21400. Ames Laboratory is operated for the U.S. DOE under Contract No. W-7405-Eng-82. The work at Ames was supported by the Director for Energy Research, Office of Basic Energy Sciences.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356911
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetic transitions at high fields in (Fe,Mn)3Si alloys : 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. 6359-6361 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the series of ordered DO3 solid solutions Fe3−xMnxSi, field-induced transitions have previously been found to occur for antiferromagnetic alloys with values of x near 1.70. The present work has determined a region of composition in which antiferromagnetism is the low-field, low-temperature state and gives the variation of the critical field as a function of temperature and composition. The critical field decreases approximately quadratically with temperature and rises to beyond 6 T in the range of composition from 1.6≤x≤1.8. Neutron diffraction indicates that the antiferromagnetic axis is shifted from the [111] direction and that in a 5 T field the antiferromagnetic component of the scattering is reduced considerably from that in zero field. However, no corresponding increase in ferromagnetic component is observed within experimental error and Arrott plots suggest the high-field state is still largely antiferromagnetic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358266
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