1. See, for example, Ø. Fischer, Appl. Phys. 16, 1(1978). 2. J. W. Lynn and R. N. Shelton, J. Appl. Phys. 50, 1984 (1979). 3. J. W. Lynn, D. E. Moncton, W. Thomlinson, G. Shirane and R. N. MAGNETIC PROPERTIES OF THE SUPERCONDUCTING ALLOY SYSTEM (Ce1-Hoc) Ru2 J. W. Lynn (University of Maryland, College Park, MD) and (National Bureau of Standards, Washington, DC) and C. J. Glinka 1-c In the magnetic superconductor system (Ce1-Ho) Ru2, Ho concentrations in excess of 30% are needed in order to completely suppress the superconducting state, while bulk susceptibility data above 27% Ho show distinct maxima as a function of temperature which are suggestive of long range magnetic order1. Additional evidence of the coexistence of superconductivity and magnetic order is provided by Mossbauer experiments which reveal the development of a hyperfine splitting below the (extrapolated) magnetic phase boundary in the "coexistence" region of concentration (~27% Ho)1. 2 To investigate the microscopic magnetic properties of this system we have carried out elastic and inelastic neutron scattering measurements as a function of temperature and magnetic field. Samples of 10%, 32% and 38% Ho, which cover the range from below to above the coexistence regime, were prepared by arc melting and subsequent heat treatment. temperature neutron powder diffraction measurements were employed to establish the concentrations to within 1%; the intensities of 18 peaks were used to refine two parameters, the ratio of Ce to Ho in the C-15 Low crystal structure and an overall scale factor. Previous measurements on a 27% Ho alloy revealed the development 3 of ferromagnetic correlations at low temperatures However, the correlation range was found to saturate at 0.5 K with no transition to long range magnetic order. If this truncation were due to a competition with the superconducting state, than at sufficiently high Ho concentrations, where the superconductivity is suppressed, a conventional ferromagnetic phase transition might occur. To test this conjecture we have Figure 1. Temperature dependence of the scattering for the 38% Ho carried out small-angle scattering measurements on the 38% alloy. Figure 1 shows that the scattering at small wavevectors increases with decreasing temperature, signaling the development of ferromagnetic correlations. However, no peak in the intensity as a function of temperature, which would be characteristic of a ferromagnetic phase transition, is found; -1 rather the scattering in the wavevector range 0.05 0.14 A increases with decreasing temperature down to 2K and then shows little further change, while at smaller wavevectors (down to 0.01 A-1, the smallest wavevector measured) the intensity continues to increase slowly. Comparison of the data with an Ornstein-Zernike correlation function suggests that the range of correlations exceeds 100 A at low temperatures, although this form for the correlation function gives a reasonable fit to the data only over a rather limited wavevector range. Thus even at Ho concentrations above the "coexistence" region the system appears to undergo a spin-freezing rather than a conventional ferromagnetic phase transition. We remark, however, that with such a large correlation range it becomes difficult experimentally to distinguish between these two cases. Indeed, for the 38% alloy we observe a small enhancement of the {111} peak below T~2K. 1. 2. 3. M. Wilhelm and B. Hillenbrand, Z. Naturf. 26a, 141 (1972) D. J. Erickson, C. E. Olsen and R. D. Taylor, Mossbauer Effect J. W. Lynn, D. E. Moncton, L. Passell and W. Thomlinson Phys Ni SPIN WAVE AND DYNAMIC CRITICAL SCATTERING IN AMORPHOUS Fe40 Ni40 P14 B6 J. W. Lynn (University of Maryland, College Park, MD) and (National Bureau of Standards, Washington, DC) and J. J. Rhyne The magnetic properties of the structurally amorphous ferromagnetic F240N140P14B6 are of particular interest because of the high permeability and extremely low coercive field this system exhibits. These properties lead not only to important commercial applications but are also interesting from a basic theoretical point of view since they imply nearly ideal isotropic behavior. The isotropy of the system has important implications with regard to the nature of the magnetic excitations in the system, namely that at long wavelengths these excitations are of the traditional spin wave type with a dispersion relation which approaches zero as the wavevector approaches zero (Goldstone's theorem). To investigate these excitations we have carried out inelastic neutron scattering measurements using the triple-axis technique. In the small wavevector region the dispersion relation is expected to follow + (1) where D(T) is the spin wave stiffness coefficient, which is temperature dependent. In the range of wavevectors K accessible (0.06 → 0.14 A A-1) we find equation 1 is indeed obeyed. Figure 1 shows D as a function of temperature, and we find that above room temperature D(T) can be well represented by Figure 1. T with Ic Temperature dependence of the spin wave stiffness coefficient. = 535 K and X≈ 0.33. As with other isotropic ferromagnets, we find the approximate relation X≈ 8, where B is the critical exponent describing the collapse of the order parameter. This is not the exponent expected from dynamic scaling theory, but in view of the relatively large wavevectors that the data represent, this cannot be viewed as a failure of the theory. We also searched for a longitudinal component to the susceptibility below T; no evidence for this component was observed, as is the case in other isotropic ferromagnets (except for COS2 only). C HIGH DENSITY LIPOPROTEIN RECOMBINANTS: EVIDENCE FOR A BICYCLE TIRE MICELLE STRUCTURE OBTAINED BY NEUTRON SCATTERING AND ELECTRON MICROSCOPY A. Wlodawer and J. P. Segrest (University of Alabama Medical Center, Birmingham, AL) We have studied the size and shapes of discoidal complexes of Apo |