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1

Digitale Medien

Magnetic correlations in amorphous Fe-Zr alloys (1988)

Rhyne, J. J. ; Erwin, R. W. ; Fernandez-Baca, J. A. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 63 (1988), S. 4080-4082

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Results of high-resolution small-angle neutron scattering (SANS) studies on amorphous alloys of composition FexZr100−x, x=90, 91, 92, show that ferromagnetic correlations exist below Tc, but that conventional long-range order is destroyed by competing exchange interactions. The transition temperatures drop with increasing iron concentration (Tc ≈226 K for Fe90Zr10 down to Tc ≈175 K for Fe92Zr8). Data taken at very low Q (0.008 A(ring)−1〈Q〈0.02 A(ring)−1) provide evidence of relatively large (≈200–≈400 A(ring)) static spin clusters which do not disorder at Tc. Superposed on this is an ordering with a second shorter length scale which shows a cusp (not divergent) at the bulk Tc. The data were fitted to a combination of a Lorentzian and a power of a Lorentzian, the latter of which represents scattering from clusters with a Maxwellian distribution of sizes.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.340554

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2

Digitale Medien

Ultrafast response micropipette-based submicrometer thermocouple (1995)

Fish, G. ; Bouevitch, O. ; Kokotov, S. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 66 (1995), S. 3300-3306

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: Submicrometer-size thermocouples at the tip of gold-coated glass micropipettes containing a platinum core were produced and tested. The response time of such thermocouples measured with different techniques appeared to be not bigger than a few microseconds. The calculations indicate that the spatial selectivity of this new class of thermocouple devices can be less than 2 μm along the pipette and less than 50 nm across the pipette. The suitability of this thermocouple for light intensity measurements with micrometer spatial resolution is demonstrated by measuring the focused beam of an argon-ion laser. In addition, such thermocouples are intrinsically suitable for applications in scanned probe microscopies. All these unique advantages make the pipette thermocouples a new and promising sensor in a variety of applications. © 1995 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1145498

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3

Digitale Medien

Frequency dependence of core loss in rapidly quenched Fe-6.5 wt. %Si (1988)

Fish, G. E. ; Chang, C.-F. ; Bye, R.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 64 (1988), S. 5370-5372

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The frequency, field, and temperature dependencies of core loss in rapidly quenched Fe-6.5 wt. %Si ribbons are reported. The annealed material exhibits (001)〈uv0〉 fiber texture, resulting in isotropic properties in plane; equivalent losses and B-H loops are seen in tape-wound toroids and in annuli punched from ribbon. Hysteresis losses predominate in the present Fe-6.5%Si up to about 1 kHz, as the thin gauge and high resistivity reduce eddy current losses from those of conventional nonoriented steels. The 2-kHz/1.0-T core losses are a factor of 6–8 higher in conventional M-15 than in Fe-6.5%Si. The core losses of Fe-6.5%Si are about 40% higher at 77 than at 373 K. The loss data are not in agreement with the predictions of Bertotti's theory.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.342374

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4

Digitale Medien

Spin-wave excitations in amorphous Fe78B13Si9 (1988)

Yu, S. C. ; Lynn, J. W. ; Rhyne, J. J. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 63 (1988), S. 4083-4085

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Inelastic neutron scattering measurements have been used to study the long wavelength spin dynamics of the high Tc amorphous ferromagnetic alloy Fe78B13Si9 (Metglas 2605S2). Spin waves were observed over the accessible wave-vector range of 0.06 A(ring)−1≤q≤0.12 A(ring)−1, for temperatures between 473 K (0.67 Tc) and 705 K (0.99 Tc). The magnon dispersion curves exhibit the conventional quadratic relationship E=D(T)q2+Δ, typical of an isotropic ferromagnet, where the small energy gap Δ≈0.05 meV is attributed primarily to the dipole-dipole interaction. An estimate of the T=0 value of D≈156 meV A(ring)2 was obtained from a plot of D(T) vs T extrapolated to low temperatures, while the Curie temperature of 710 K was obtained from the extrapolation of D(T) to zero at high temperatures. Spin-wave linewidth data for T/Tc≈0.95 showed the q4 wave-vector dependence expected for magnon-magnon interactions.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.340556

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5

Digitale Medien

Reply to "Comment on ‘Small-angle neutron scattering evidence for the absence of long-range magnetic order in amorphous Fe91Zr9' '' [J. Appl. Phys. 57, 3407 (1985)] (1987)

Fish, G. E. ; Rhyne, J. J.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 61 (1987), S. 454-455

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Experimental evidence is presented and reviewed that amorphous Fe91Zr9 does not exhibit conventional long-range ordered ferromagnetism below its Tc=210 K, but rather enters a state characteristic of a strongly exchange-frustrated system in which the ferromagnetic correlations are quite short range (less than 30 A(ring)) as determined by small-angle neutron scattering (SANS). At a lower temperature the SANS develops a Lorentzian-squared component to the line shape which is evidence of cluster spin freezing. Inelastic scattering data show no resolvable spin-wave peaks and place an upper limit of 12–15 meV A(ring)2 on the spin stiffness D. The anomalously small ratio of D/Tc is further evidence of a system near a multicritical point concentration.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.338798

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6

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Polarization analysis of the magnetic excitations in Invar and non-Invar amorphous alloys : 37th Annual conference on magnetism and magnetic materials (1993)

Lynn, J. W. ; Rosov, N. ; Fish, G.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 73 (1993), S. 5369-5371

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Conventional spin wave theory works remarkably well in describing the spin dynamics of both Invar and non-Invar isotropic ferromagnets, with the important exception that for Invar systems the magnetization decreases much more rapidly with temperature than can be explained based on the measured spin wave dispersion relations. We have been carrying out triple-axis polarized inelastic neutron scattering experiments on the amorphous ferromagnets Fe86B14 (Invar system) and Fe40Ni40P14B6 (METGLAS(large-closed-square) 2826) in order to separate the longitudinal magnetic fluctuations from the transverse (spin wave) excitations, and thereby determine if the presence of longitudinal excitations might resolve this discrepancy. The present measurements exhibit longitudinal excitations below Tc, but in both materials. Possible interpretations of the results are discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.353733

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7

Digitale Medien

Spin dynamics of amorphous Fe90−xNixZr10 (invited) (1990)

Fernandez-Baca, J. A. ; Rhyne, J. J. ; Fish, G. E. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 67 (1990), S. 5223-5228

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: 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.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.344618

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8

Digitale Medien

Small-angle neutron scattering evidence for the absence of long-range magnetic order in amorphous Fe91Zr9 (1985)

Rhyne, J. J. ; Fish, G. E.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 57 (1985), S. 3407-3409

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Small-angle neutron scattering (SANS) studies of an amorphous Fe91Zr9 alloy have shown that there is no transition to long-range magnetic order in contrast to previous bulk magnetization results which indicated a transition to a ferromagnetic state at 220 K followed by a reentrant spin-glass state near 60 K. The scattering line shape is Lorentzian in Q down to below 150 K and yields a spin correlation length which reaches a maximum of only 27 A(ring) at the transition T C=210 K and exhibits an essentially constant plateau of 23 A(ring) down to helium temperature, with no evidence of a second transition in the 60–80 K range. The line shape departs from Lorentzian below about 120 K and can be represented by a Lorentzian plus Lorentzian-squared cross section as appropriate for a system in which long-range order has been replaced by a frozen cluster configuration. The absence of ferromagnetic order in Fe91Zr9 at Fe concentrations far above the percolation threshold suggests the presence of a very broad distribution of exchange fields arising from the random Fe site coordinates.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.335110

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9

Digitale Medien

Spin dynamics of the amorphous Invar alloy Fe0.86B0.14 (1985)

Fernandez-Baca, J. A. ; Lynn, J. W. ; Rhyne, J. J. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 57 (1985), S. 3545-3547

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: High-resolution neutron scattering studies have been made of the long wavelength spin excitations in a ribbon sample of amorphous Fe0.86B0.14, which exhibits Invar properties. Spin waves were observed in the wave vector range 0.05 A(ring)−1≤q≤0.12 A(ring)−1 at temperatures between 300 K (0.54 Tc) and 500 K (0.90 Tc). The spin wave energies are well described by a dispersion relation E=Dq2+Δ. The small energy gap Δ of ≈0.04 meV is attributed primarily to the dipole-dipole interaction. The stiffness constant renormalizes with temperature as D=D(0)[1.0−0.86 (T/Tc) 5/2] in the range of temperatures under study, with D(0)=132 meV A(ring)2. This value of D(0) is approximately twice as large as that calculated from the T3/2 coefficient of the magnetization, a discrepancy common to many Invar materials. Plots of the intrinsic linewidths against q4 and T2 reveal that the data are consistent with the Γ∝q4[Tln(kT/E)]2 dependence predicted for a Heisenberg ferromagnet. There are no anomalies in the spin-wave lifetimes at long wavelengths which appear to relate to the Invar effect seen in the FexB1−x system.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.335056

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10

Digitale Medien

Low-temperature spin waves in amorphous Fe90−xNixZr10 (1988)

Fernandez-Baca, J. A. ; Lynn, J. W. ; Rhyne, J. J. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 63 (1988), S. 3749-3751

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Inelastic neutron scattering measurements have been performed on rapid-quenched ribbons of Fe90−xNixZr10 (x=1,5,10) to measure the small wave-vector spin-wave spectrum. At all three concentrations a quadratic dispersion relation typical of an isotropic ferromagnet is observed, but with anomalous properties at low temperatures. For x=5 and 10 the excitations are found to broaden considerably for temperatures ≤0.3 Tc. For x=1 the spin waves not only broaden for T≤0.5Tc, but the spin-wave energies decrease monotonically with decreasing temperature while a resolution-limited quasielastic component of the scattering develops. These results are consistent with a picture of competing ferromagnetic and antiferromagnetic interactions, with reentrant spin-glass behavior evident if the frustration is sufficiently strong.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.340655

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