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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6543-6545 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report measurements of the intensity and position of the satellites arising from the helimagnetic structure of holmium in magnetic fields applied along different crystal axes, concentrating on lock-in effects at commensurate values of the spiral wave vector τ. We have made the first observations of the lock-in at τ=1/5 near 42 K in a 3 T c-axis field as well as the lock-in at τ=1/4 in a 3 T b-axis field. We have also observed a lock-in at τ=5/18 in a b-axis field near the Néel temperature of 132 K, in contrast to an earlier reported value of 8/29. This illustrates the origin of the splitting previously reported by us in magnetization and dilatometric measurements.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6229-6231 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The complex magnetic behavior of holmium is a well-established experimental fact and has been studied by a variety of experimental techniques, including magnetization, x-ray diffraction, thermal expansion, and heat capacity. Our recent studies have focused on using neutron diffraction to study the temperature and field dependence of the helimagnetic structure. The pitch of the helix is described by τ, the spiral wave vector. τ usually varies smoothly with temperature but tends to lock in at various values that are commensurate with the lattice when a field is applied. These lock-ins provide clues to the nature of the different magnetic phases and, up to now, all the lock-ins have corresponded to features of the magnetic phase diagram obtained from magnetization measurements. However, recent experiments have revealed a previously unobserved lock-in at τ=2/9 rlu in a 1.4 T b-axis field. It shares the same general features of other lock-ins except that it does not correspond to any feature of the magnetic phase diagram.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5341-5343 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutron scattering techniques have been used to measure the nature of the phase transition in erbium at TN=87 K from paramagnetism to an incommensurate longitudinally ordered phase with q=0.283 along c at TN. A high-purity crystal showed normal critical scattering in the paramagnetic state with a different correlation length in the basal plane and along c. It is found that γ=0.96±0.06 and both correlation lengths diverge with the same critical exponent ν=0.49±0.02 for a range of reduced temperature from 0.0015 to 0.07. In the ordered state, power-law behavior was observed with β=0.48±0.02 for reduced temperatures between 0.005 and 0.04. Below TN the intensity of the third harmonic varied as the cube of the reduced temperature. All these observations correspond to mean-field behavior.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report measurements of the intensity and position of the satellites arising from the helimagnetic structure of Ho in 1.4 and 3 T b-axis magnetic fields. There are a number of lock-in effects at commensurate values of the spiral wave vector τ; here we report on those in the temperature range 115–132 K. We confirm our previous observation of the lock-in at τ=5/18 between 125 K and the Néel temperature (132 K). We have discovered a two-phase region in which the 5/18 phase coexists with an incommensurate phase. In this two-phase region, the proportion of the 5/18 phase increases with temperature from onset at 119 K to full lock-in at 125 K. The existence of this two-phase region may have significant influence on interpretation of the magnetic phase diagram.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3734-3744 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pump-probe experiments in GaAs/AlGaAs multiple quantum well samples are described using both picosecond and femtosecond laser pulses in different polarization configurations. The excitonic and free carrier components of exciton absorption saturation were analyzed as a function of well width. The relative importance of phase space filling, Coulomb screening and broadening contributions was determined from polarization and laser bandwidth dependencies via spin-dependent and spin-independent components. A five-level model was used to fit the data and nonlinear coefficients for the individual contributions were determined for each well width. The Coulomb contributions arising from screening and broadening of the excitons was found to dominate the absorption bleaching using picosecond pulses, whereas phase space filling was largest in the femtosecond regime. Exciton phase space filling was found to be four times larger than free carrier phase space filling at narrower well widths. A sublinear dependence of exciton broadening with carrier density was observed. © 1999 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5883-5885 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: While pure chromium undergoes a first-order antiferromagnetic transition, thermal expansion measurements have indicated that the addition of small amounts of vanadium and molybdenum make the Néel transition continuous. A neutron diffraction study of a single crystal of Cr(0.5% V) showed no discontinuity in magnetic Bragg satellite intensity at the Néel temperature, TN=254 K, that would indicate a first-order transition. Complicated behavior of the satellite intensities near the transition temperature is attributed to inhomogeneous strain in the sample. The satellite intensity showed a linear temperature dependence over a range of at least 100 K below TN.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5262-5264 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamic magnetic susceptibilities, χ(Q,ω), of Cr+0.2 at. % V and chromium were measured in the temperature range (TN−15 K)〈(TN+20 K) by neutron scattering. Here, χ (Q,ω) of Cr+0.2 at. % V is clearly incommensurate, in contrast to the apparently commensurate inelastic scattering seen in pure chromium. The observed form of the scattering for each material does not qualitatively change in going from above TN (paramagnetic) to below it (antiferromagnetic). Since no discontinuity in elastic magnetic intensity was observed in the alloy crystal, analysis in terms of the critical phenomena of a second-order phase transition can now be attempted.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3412-3414 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spin waves in ferromagnetic USe have been measured by inelastic neutron scattering. Previous measurements on a multidomain USe sample show that the spin wave branch has a zone center frequency of ≈9 THz, and that the spin waves are intrinsically broad. New measurements on a single domain sample show that, in addition, the spin wave is unpolarized. This behavior is unlike that of a classical ferromagnet, in which the polarization is transverse, but similar to behavior observed in some singlet ground state systems.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 936-938 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report time resolved studies of optically induced circular dichroism in room temperature GaAs/AlGaAs multiple quantum wells to resolve spin-dependent and spin-independent contributions to exciton saturation. Phase-space filling and Coulomb contributions were separated by spin dependence while the effects of broadening and screening were distinguished using different pulse bandwidths. Bound and free carrier contributions were compared by observing the temporal dependence of the circular dichroism on femtosecond timescales. The spin independent contribution to exciton saturation was found to be independent of whether the carriers were bound or free. © 1997 American Institute of Physics.
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  • 10
    Publication Date: 1990-07-16
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
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