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  • 1
    Electronic Resource
    Electronic Resource
    Neutron Diffraction from Orientationally Disordered Crystals (1988)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 27-28 (June 1988), p. 35-48 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/03/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.27-28.35.pdf
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  • 2
    Electronic Resource
    Electronic Resource
    The Non-Resonant Magnetic X-ray Scattering Cross Section of MnF2. 1. Medium X-ray Energies from 5 to 12keV (1996)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 52 (1996), S. 427-437 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: To demonstrate the possibilities of non-resonant magnetic X-ray diffraction, data taken on the antiferromagnetic model system MnF2 in a medium X-ray energy range from 5 to 12 keV are presented. An experimental set-up for the measurement of magnetic X-ray diffraction is introduced that employs a new design for a highly flexible polarization analyzer for synchrotron X-ray diffraction based on 90° Bragg reflection from a single-crystal. The analyzer has been successfully tested on beamline W1 at HASYLAB by measuring the polarization of the primary photon beam and of the 400 charge peak of an MnF2 single-crystal. Subsequently, the analyzer was used to explore the polarization dependence of the non-resonant magnetic X-ray scattering cross section of this sample, complemented by measurements of the directional dependencies without polarization analysis. In the latter configuration, count rates as high as 3800 photons s−1 and a peak-to-background ratio of 160:1 were obtained. A method to determine the direction of the magnetic moments with respect to the crystalline axes is presented. The results give experimental support for the theoretical form of the non-resonant magnetic X-ray scattering cross section and at the same time provide a feasibility test for a general magnetic structure determination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S010876739600075X
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  • 3
    Electronic Resource
    Electronic Resource
    First observation of bulk magnetic scattering using high-energy X-rays (1993)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 49 (1993), S. 679-682 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Today, the most powerful methods for the investigation of magnetic structures are magnetic neutron diffraction and synchrotron-X-ray scattering in the energy range 3–15 keV. This paper reports the first successful experiment to exploit a new technique: the magnetic diffraction of hard X-rays with energies exceeding 80 keV. This technique combines some of the advantages of each of the aforementioned methods: namely high Q-space resolution (10−4 Å−1 radial and 10−5 Å−1 tangential) and bulk sensitivity (absorption length 〉〉 1 mm). It is shown that, compared to nominally 10 keV X-ray scattering, enhancement factors of several orders of magnitude can be obtained for the magnetic signal, owing to the increase in penetration depth. The magnetic cross section for these very hard X-rays is discussed, the new technique is compared with the existing methods and a preliminary experiment on MnF2 is reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767393003423
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  • 4
    Electronic Resource
    Electronic Resource
    The Non-Resonant Magnetic X-ray Scattering Cross Section of MnF2. 2. High-Energy X-ray Diffraction at 80keV (1996)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 52 (1996), S. 438-449 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Results of high-energy non-resonant magnetic X-ray diffraction experiments performed on the model system MnF2 at a photon energy of 80 keV are presented. A surprisingly high peak intensity of the magnetic 300 reflection of 13000 photons s−1 in the three-crystal mode and 19000 photons s−1 in the two-crystal mode, with a peak-to-background ratio of 230:1 and 10:1, respectively, has been achieved. At 80 keV, the penetration depth is 7 mm. When the path length of the beam through the crystal is varied, the effect of volume enhancement of the intensity diffracted by magnetic reflections is demonstrated. The Q dependence of the magnetic and the charge Bragg reflections has been measured and agrees well with theory. The measurement of the temperature dependence of the sublattice magnetization allows a very accurate determination of the critical exponent β = 0.333 (3) and the Néel temperature TN = 67.713 (2) K. Finally, the multiple charge scattering is discussed, which is very pronounced for the magnetic reflections of MnF2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767396000773
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  • 5
    Electronic Resource
    Electronic Resource
    X-ray and neutron investigation of the structure and disorder in dicalcium barium acrylate (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 448-455 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768193011887
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  • 6
    Electronic Resource
    Electronic Resource
    The magnetic structure of the langbeinite K2Mn2 (SO4)3 (1988)
    Springer
    Physics and chemistry of minerals 16 (1988), S. 246-249 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract K2Mn2(SO4)3 orders magnetically at TN= 1.75 K. One of the orthorhombic cell edges of the low temperature Langbeinite structure becomes doubled in the magnetically ordered state. The antiferromagnetic spin structure found is characterized by weak or vanishing molecular fields due to nearest neighbours. There are no indications of magnetic order down to 1.45 K in the isomorphic compound K2Co2 (SO4)3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00220692
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  • 7
    Electronic Resource
    Electronic Resource
    Biquadratic exchange and critical behaviour in the diluted antiferromagnet EuxSr1−xTe (1993)
    Springer
    The European physical journal 92 (1993), S. 475-487 
    Details
    ISSN: 1434-6036
    Keywords: 75.30.Et ; 75.30.Kz ; 75.40.-s
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Magnetization, specific heat, magnetocaloric effect, and neutron diffraction measurements have been performed in order to better understand the magnetic interactions and phase transitions in the diluted antiferromagnetic system EuxSr1−xTe. Due to the low Néel temperature ofT N =9.8 K and the associated small critical field ofB C (T=0)=7.5 T, EuTe provides the opportunity to change the angle between the antiferromagnetic moments continuously between 180° and 0° by applying a magnetic field and allows thus to probe the type of the magnetic interaction. It is found that in addition to the common bilinear Heisenberg exchange mechanism there is evidence for a small biquadratic exchange term, which has important consequences on the critical behaviour of EuxSr1−xTe. In the case of EuTe the biquadratic exchange supports the antiferromagnetic order, such that virtually no anisotropy exists and this restricts the anti-Herromagnetic (AF) to spin-flop (SF) transition toB 0=0. On dilution with strontium, the biquadratic interaction decreases strongly and changes its sign at x≈0.83 thus favouring the perpendicular moment orientation. This acts like an anisotropy on the dominating antiferromagnetic bilinear interaction and shifts the AF-SF phase line to finite fields which reach values of 0.3 T forT→0. No bicritical behaviour is observed, but instead, the SF phase is the state of lowest energy in a small temperature interval belowT N . The critical exponent α(x) of the specific heat decreases in a non-linear way with dilution starting from a large positive value for EuTe. α(x) is close to the Heisenberg value −0.12 nearx≈0.83 where the biquadratic interaction is zero. The same applies for the exponent β of the sublattice magnetization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01320511
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  • 8
    Electronic Resource
    Electronic Resource
    Spin waves and exchange interactions in the antiferromagnetic garnets with Fe3+ in the octahedral sites (1993)
    Springer
    The European physical journal 92 (1993), S. 443-449 
    Details
    ISSN: 1434-6036
    Keywords: 75.25.+z ; 75.30.Et
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The results of an inelastic neutron scattering study of the spin wave spectrum for the garnet Fe2Ca3Si3O12(FeSiG) are presented. We compare the exchange parameters for this garnet and for the Ge-species (Fe2Ca3Ge3O12(feGeG)) having the same magnetic structure. We relate the differences found with structural information from powder neutron diffraction. In this way the super exchange paths viap σ orbitals of intermediate oxygen atoms can be identified. We discuss the effect of a small number (3.2(5)%) of Mn2+ impurities in the 24c sites. These lead to an effective ferromagnetic exchange between the Fe3+ ions and drastically renormalize the average exchange constants. An estimate for the Fe3+−Mn2+ indirect exchange between a and c sites of 6(1) K is obtained. The exchange parameters for the pure FeSiG are found to beJ 1=1.16(4) K,J 1=0.96(4K andJ 2=−1.24(4) K for nearest and next nearest neighbours, respectively. These values apply for a moment of 4.02(4) μB per iron atom as obtained from a structure refinement of powder diffraction data. Finally we present results for FeSiG of a high resolution study of the excitations at the zone centre in an attempt to verify our earlier findings of a quantum spin wave gap for FeGeG. In contrast to the earlier measurements, we could follow the acoustical branch to much lower energies using a timeof-flight spectrometer. We found indications for a crossing of the two low lying spin wave branches, the acoustical one extrapolating to the anisotropy gap of 0.005 THz and the “antiphase” branch extrapolating to the quantum gap of 0.02 THz.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01320506
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  • 9
    Electronic Resource
    Electronic Resource
    Investigations of the sublattice magnetizations M (T) in antiferromagnets with fourth-order exchange interactions: Eu Sr Te (1999)
    Springer
    The European physical journal 8 (1999), S. 217-224 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 75.30.Et Exchange and superexchange interactions - 75.30.Kz Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.) - 75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We present a neutron scattering study of the temperature and composition dependence of the MnO-type superstructure reflection intensities in the diamagnetically diluted antiferromagnetic compounds EuxSr1-xTe. In these materials antiferromagnetic biquadratic and ferromagnetic three-spin interactions have been identified recently. These fourth-order non-Heisenberg interactions are able to create their own order parameter which is believed to govern the order of the transverse moment components and which, hence, is directed perpendicular to the common Heisenberg order parameter. The observed MnO-type diffraction intensities originate in the sublattice magnetizations, , of both order parameters. Due to the different composition dependencies for biquadratic interaction processes and three-spin interaction processes , the ferromagnetic three-spin interactions dominate for x 〉 x c =0.85, while for x 〈0.85 the antiferromagnetic biquadratic interactions dominate. Associated with this sign change in the fourth-order interaction sum the transverse order parameter changes from the antiferromagnetic MnO type for x 〈0.85 to ferromagnetic for x 〉0.85. This is noticed as a sudden decrease of the low-temperature MnO scattering intensities at x c =0.85. Although susceptibility measurements reveal clearly a ferromagnetic component for x 〉0.85 no ferromagnetic Bragg intensities were observed in standard neutron scattering spectra using EuTe powder samples. We explain this by the competition of antiferromagnetic biquadratic and ferromagnetic three-spin interactions whereby a disturbed ferromagnetic superstructure may be generated which gives rise also to weak MnO-type diffraction lines. It is found that the resulting obeys a T2 law until a temperature as large as 0.75TN irrespective of the nature of the transverse order parameter. The T2 law must, hence, be common to both types of order parameter showing that the fourth-order interactions re-define the spin dynamics of both completely. From the linear composition dependence of the normalized T2 coefficient the existence of three-spin interactions is again confirmed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510050684
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  • 10
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    Erratum: Spin dynamics of the magnetocaloric compound MnFe4Si3 [Phys. Rev. B 96 , 104407 (2017)] (2018)
    American Physical Society
    Details
    Publication Date: 2018-12-04
    Print ISSN: 2469-9950
    Electronic ISSN: 2469-9969
    Topics: Physics
    Published by American Physical Society
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