Small angle neutron scattering in Ni3Al

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Abstract
The temperature dependence of small angle neutron scattering in weakly ferromagnetic Ni3Al has been investigated by means of multi‐detector small‐angle spectrometers at A.E.R.E. Harwell and I.L.L. Grenoble. Measurements are reported in three stoichiometric samples with residual resistivity ratios [RRR=ρ(293 K)/ρ(4.2 K)] of up to 40 and in a Ni rich specimen (Ni75.4Al24.6). The cross sections in stoichiometric specimens exhibit an approximately linear rise with temperature well below the Curie point (TC=41±1 K), a peak around TC and a fall approximately proportional to (T−TC)−1 above TC. This behaviour is interpreted in a Ginzburg‐Landau model of magnetic fluctuations involving a single adjustable parameter, from which a spin correlation length around TC and an effective spin‐wave stiffness well below TC may be derived. Finally the possible qualitative features of the overall transverse magnetic fluctuation spectrum of Ni3Al are examined and a simple model is noted which can account for the observed fall in magnetization at low temperatures.