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  • 1
    Digitale Medien
    Digitale Medien
    Surface roughness and long-range order of a semi-infinite ferromagnet : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5981-5983 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We consider the effect of random surface roughness on a semi-infinite ferromagnetic film. We calculate the magnetization as a function of distance from the surface and the spin-spin correlation as a function of lateral separation. We show that, even in the absence of crystalline anisotropy or an external field, the surface of the ferromagnet is stable against random torques created by the roughness. Near the surface, the magnetization reduction is inversely proportional to the square of a "healing'' length λ0≡(D/2πM0)1/2, where D is an exchange stiffness and M0 is the saturation magnetization. The correlations in fluctuations of the magnetization orientation decay exponentially with distance parallel to the surface, λ0 being in the exponent. In contrast, fluctuations decrease only as the reciprocal of the square of the distance perpendicular to the surface. Results are discussed and compared with other calculations of the effects of random surface perturbations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.353490
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  • 2
    Digitale Medien
    Digitale Medien
    A phenomenological theory for the temperature dependence of the antiferromagnetic coupling in thin-film sandwiches and multilayers (abstract) : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5879-5879 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Recent magnetoresistance experiments1,2 on Fe/Cr/Fe sandwiches and superlattices show that the critical magnetic field for saturation varies linearly with temperature from liquid helium to room temperature. The drop in critical field is as large as 30%, even though the reduction in Fe magnetization is negligible over this temperature range. In order to gain some insight into the physical origin of this softening of the critical field, which is a measure of the antiferromagnetic interlayer coupling, we have studied a phenomenological model of an Fe/Cr/Fe sandwich structure which consists of two Fe films coupled at their interface by an antiferromagnetic exchange at zero temperature. The Fe films themselves are ferromagnetic and subjected to an external field and uniaxial in-plane anisotropy. The Fe spins are confined to the film plane. The temperature dependence of the critical field, i.e., the field below which the spins in the two films deviate from the direction of the field, arises from fluctuations in these spin deviations, which are present for any temperature greater than zero. Using an approximation in which these fluctuations are treated classically, the critical field decreased linearly with temperature, with a coefficient that increases logarithmically with the transverse dimension of the films. Interpreting this length to be of the order of the grain size in polycrystalline films or a coverage terrace width in epitaxially grown material, we can directly relate the temperature variation of the antiferromagnetic interaction to film quality. The larger this dimension, the greater the decrease of the coupling with temperature; hence, "better'' films are expected to show weaker (or zero) coupling at room temperature. Conversely, the magnetization of the Fe films is not critically dependent on this dimension. Extension of the model to include spin-wave effects will be discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.350117
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  • 3
    Digitale Medien
    Digitale Medien
    The effect of volume on magnetization in RxY1−xCo2 pseudobinaries (abstract) : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5711-5711 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: There is experimental1 and theoretical2 evidence that the cubic Laves phase compound YCo2, paramagnetic at its equilibrium volume, will become ferromagnetic with only a slight increase in volume. This volume sensitivity of Co-containing Laves phase compounds must therefore be considered when addressing the problem of the origin of the Co magnetic moment in pseudobinaries RxY1−xCo2, where R is any rare earth element with a net spin moment. In this paper we augment the itinerant picture describing the effect of the rare earth spin on the Co magnetization3 by taking into account the changes in volume brought about by the substitution of the rare earth for yttrium. We obtained the coefficients of the Landau expansion of the free energy by fitting the expansion to the calculated energy versus moment curves of YCo2 for various volumes.2 (These energies were calculated in Ref. 2 using the fixed-spin-moment method, within the local-spin-density approximation). Thus, for example, the substitution of Gd forces the formation of Co moments not only because of the Gd spin, but because of the increase in latttice constant, whereas the rare earths heavier than Tb have smaller lattice constants and are less likely to induce a moment on the Co sublattice. Results are presented for the critical fields necessary for magnetic ordering and for the Co magnetic moment as a function of the rare earth substitution.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.348939
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  • 4
    Digitale Medien
    Digitale Medien
    Amorphization of TbFe3 by nitrogen absorption : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5733-5735 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The nitrogenation process of the TbFe3 intermetallic compound was studied by heat treating the alloy between 573 and 873 K in a nitrogen atmosphere. The structural and magnetic properties of the nitrogenated samples were characterized by x-ray diffraction (XRD), Mössbauer spectroscopy, and magnetic measurements. The magnetic moments of the nitrogenated samples were found to be a function of the annealing temperature and showed a minimum for the sample heat treated at 673 K. The XRD pattern of this sample (673 K) showed that the Bragg peaks of the 1-3 phase had completely disappeared and were replaced by a broad maximum indicating a breakdown of the TbFe3 structure into an amorphous phase. The room-temperature Mössbauer spectrum of the same sample consisted almost entirely of a quadrupole-split doublet plus a small amount of α-Fe and TbFe3. This doublet split into a broad spectrum upon cooling which is typical of amorphous rare-earth–transition-metal compounds. For samples heat treated at higher temperatures, the amount of α-Fe and TbN phases gradually increased. This nitrogenation process is unlike that of R2Fe17. In this study, nitrogen atoms do not go into the interstitial sites. Instead, they create a ferromagnetic (TC≈215 K) amorphous phase of Tb, Fe, and N which is stable over a wide temperature range.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.353607
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  • 5
    Digitale Medien
    Digitale Medien
    The temperature, concentration phase diagram for Tb1−xDyxZn: Failure of crystal field theory (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5792-5794 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have calculated the free energy of a crystal field model designed to reproduce the magnetic temperature, composition phase diagram for Tb1−xDyxZn alloys. Using fourth- and sixth-order coefficients consistent with single-ion theory, it was found to be impossible to reproduce the experimental phase boundaries. A reasonable fit to the entire diagram was obtained when the coefficients were chosen to be of the same sign for Dy and Tb, rather than of opposite sign, as required by single-ion theory. To explain this discrepancy, a model is introduced which includes a contribution to the crystal field coming from quadrupole–quadrupole interactions. It is argued that the reason for the success of the calculation using coefficients of the same sign is directly related to the dependence of the strength of the quadrupole coupling on the square of the second-order Stevens factor. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.372524
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  • 6
    Digitale Medien
    Digitale Medien
    Magnetization and magnetostriction of Tb1−xDyxZn single crystals (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6250-6252 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Magnetization, magnetostriction, and elastic modulus measurements were made on single crystal specimens of Tb1−xDyxZn. Easy axis magnetization rotation as much as 26° were observed in the (001) plane of Tb0.75Dy0.25Zn below 33 K. From these measurements, values of the K4/K8 anisotropy ratios were calculated. No easy axis magnetization rotation was observed in the x=0.6 and x=0.8 single crystals. Magnetostriction and modulus measurements at 77 K in Tb0.4Dy0.6Zn showed a saturation magnetostriction of ∼5×10−3 and a maximum magnetomechanical coupling factor of 0.96. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.370236
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  • 7
    Digitale Medien
    Digitale Medien
    Anomolous ΔE effects in TbDyZn alloys : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6216-6218 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The temperature dependence of Young's modulus has been measured for a series of Tb1−xDyxZn pseudobinary compounds with x ranging from 0 to 1. From the sharp dips in the modulus vs temperature data, the reorientation transition temperatures have been determined, and the magnetic phase diagram deduced. Magnetization measurements taken on the same samples show less pronounced features at the corresponding temperatures. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.362075
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  • 8
    Digitale Medien
    Digitale Medien
    Stress effect on the magnetization of Dy in the Dy/DyFe2 eutectic : 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. 7027-7029 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The magnetization of the alloy DyFe1.5 was studied as a function of temperature from 50 to 300 K in a range of magnetic field up to 10 kOe. Metallographic studies showed the existence of a eutectic phase containing both DyFe2 and elemental Dy embedded in the DyFe2 matrix. The presence of elemental Dy was observed in the magnetization data through a cusp in the temperature dependence of the magnetization at 178 K and an increase of the magnetization starting at 130 K and continuing to 80 K. While the first feature occurs at precisely the Néel temperature of bulk Dy, the second contrasts with the jump at the Curie temperature of 89 K observed in low fields in bulk single-crystal Dy. The more gradual increase in magnetization observed in the DyFe1.5 alloy is attributed to variations in stress to which the Dy is subjected. The temperature dependence of the magnetic moment from 80 to 130 K is modeled as arising from a collection of Dy particles of varying Curie temperatures. This variation is in turn caused by the stress distribution. Curie temperature distributions are found for a range of magnetic fields and then are extrapolated to zero field in order to eliminate the effect of field. The calculations indicate that a significant amount of the Dy remains in the helimagnetic phase down to zero temperature.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.358076
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  • 9
    Digitale Medien
    Digitale Medien
    Critical behavior of cubic magnetostrictive materials under stress : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5417-5419 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Critical points and lines in magnetic field space define the boundaries of different magnetization states between which the magnetization may "jump," leading to hysteresis. We calculate the changes in these boundaries due to magnetoelastic coupling to applied stresses, and obtain the critical stresses required to eliminate jumping in specific cases. These results may provide a way of reducing or eliminating hysteresis in large magnetostriction materials. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.364557
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  • 10
    Digitale Medien
    Digitale Medien
    Magnetic moment and hyperfine field on Fe sites in RFe6Sn6 compounds : The 7th joint MMM-intermag conference on magnetism and magnetic materials (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6983-6985 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Electronic structure and hyperfine fields are calculated for antiferromagnetic YFe6Sn6 using the linear muffin-tin orbital method. The results show that Fe atoms have a strong ferromagnetic character with a full majority-spin band. The Fe moment is 2.2 μB while the Fermi contact term contributes a hyperfine field of 20 T at the natural lattice parameters. The hyperfine field is close to the experimental value of 22 T measured at low temperature. The calculation shows that the core s electrons contribute 24 T to the hyperfine field, but the 4s electron contributes 4 T in the opposite direction. Calculations using different unit cell volumes reveal that only the core electron contributions to the hyperfine field are proportional to the Fe magnetic moment with a conversion factor of 11.8 T/μB; the 4s contribution is not. The large local Fe moment and small hyperfine field are similar to those found in Fe2P and FeO. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.367852
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