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  • 1985-1989  (5)
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Material
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Random-field critical scattering (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 3291-3293 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The quasielastic scattering of neutrons in d=3 (Fe0.6Zn0.4F2) and d=2 (Rb2Co0.85Mg0.15F4) random-field Ising model (RFIM) systems in the critical region has been studied. A sharp phase transition at Tc(H) with new critical behavior is observed at d=3 whereas the phase transition is destroyed at d=2 in the presence of a random field. At d=3 the antiferromagnetic state is stable for all T and H below Tc(H) whereas the field-cooled domain state shows irreversible behavior. Hence the lower critical dimensionality dl of the RFIM 2≤dl〈3 in agreement with earlier birefringence experiments. The marked differences between the properties of the d=2 and d=3 RFIM system are elucidated. Our work strongly suggests that all previous neutron studies of similar systems have been incorrectly interpreted as regards dl.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335461
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    High-field magnetization measurements of the metastability boundary in a d=2 random-field Ising system (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 3297-3299 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The d=2 random-field Ising system Rb2Co0.85 Mg0.15F4 has been studied using pulsed, high-field magnetization M measurements. A relatively sharp metastability boundary TF(H) has been discovered which separates a frozen region below from an equilibrium one above TF(H). TF(H) scales as does the (destroyed) phase transition "Tc(H)'' as TN −TF(H) ∝H2/φ, with the measured crossover exponent φ=1.8±0.1 in good agreement with the d=2 susceptibility exponent γ=7/4. As measured in the pulsed field experiment, TF(H) lies well below "Tc(H)'' but above the value of TF(H) obtained from recent neutron scattering studies. The difference in the two values of TF(H) is attributed to the log t time dependence of the approach to equilibrium and to magnetocaloric effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335127
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Hysteresis, metastability, and time dependence in d=2 and d=3 random-field Ising systems (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 3294-3296 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The hysteretic properties of random-field Ising model (RFIM) systems were studied. Using neutron scattering, a relatively narrow metastability boundary TF(H) in the d=2 (d=dl) RFIM system Rb2Co0.85Mg0.15F4 was found to lie well below the rounded specific heat peak "Tc(H)'' of the (destroyed) phase transition. TF(H) scales as TN−TF(H)∝H2/φ with the RF crossover exponent φ=1.74±0.02. At TF(H), equilibrium is approached logarithmically with time. In the d=3 (d〉dl) RFIM system Fe0.6Zn0.4F2 AF order was found to be stable against changes of T and H below the observed sharp phase transition boundary Tc(H), while the field-cooled domain state was not. Capacitance measurements in Fe0.68Zn0.32F2 established that equilibrium prevails for T≥Teq(H) which is slightly above Tc(H). Pronounced logarithmic time dependence is observed at T(approximately-less-than)Tc(H).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335126
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    μ+ SR studies on pure MnF2 and site-diluted (Mn0.5Zn0.5)F2SR studies on pure MnF2 and site-diluted (Mn0.5Zn0.5)F2 (1986)
    Springer
    Hyperfine interactions 31 (1986), S. 313-318 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Positive muon spin rotation and relaxation measurements have been carried out on the antiferromagnets, pure MnF2 and site-diluted (Mn0.5Zn0.5)F2, above and below the Néel temperature TN using single-crystal specimens. Two different muon signals have been found in the pure MnF2; with the precession frequency υA for the site A and υB for the site B measured in zero external magnetic field at T=5 K. We propose a picture that the signal from the A site represents the “muonium” state, and discuss the characteristic features of muonium in magnetic materials. The spin relaxation rate 1/T1, measured in zero external field, decreases rapidly with decreasing temperature below TN. The mechanism of the spin relaxation above TN is explained by the exchange fluctuations of the Mn moments, while below TN by the Raman scattering of spin waves. At the same normalized temperature T/TN, 1/T1 observed in the diluted (Mn0.5Zn0.5)F2 is significantly larger than that in the pure MnF2 below TN. The difference between the pure and diluted systems is related to the large spectral weight of low-energy magnons in (Mn0.5Zn0.5)F2 found by neutron scattering.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02401574
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Observation of muon level-crossing resonance in antiferromagnetic MnF2 (1986)
    Springer
    Hyperfine interactions 31 (1986), S. 29-34 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report the observation of μ+ Level-Crossing Resonances (LCR's) in the ordered phase of an antiferromagnetic material. Two LCR's were observed in MnF2 as a function of longitudinal magnetic field in the temperature range between 10K and 65K. Both are attributed to a muon in an interstitial octahedral-like site. The low field resonance is attributed to a muon-nuclear spin flip-flop transition involving the two nearest neighbour19F nuclei. The high field resonance occurs when the applied field cancels the local hyperfine field on the muon. The positions and widths of the LCR's were seen to scale with the sublattice magnetization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02401535
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    Paper (German National Licenses)
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