Magnetic Fluctuations in Paramagnetic Mn0.81Ni0.19

Full text: The nature of the magnetic fluctuations present in electronically itinerant 3d transition metals and their alloys still remains incompletely described. For λ MnNi alloys, the itinerant character of the magnetisation is indicated by the bulk magnetic susceptibility continuing to increase as the temperature is raised above the Neel temperature. The inelastic neutron scattering from a paramagnetic Mn0.81Ni0.19 single crystal has been measured at 3 temperatures above the Neel temperature, approximately equal to 430 K for this system. The temperatures studied were 450 K, 585 K and 700 K. Antiferromagnetic correlations are observed to be present at all temperatures studied, indicated by the scattering peaking at the (100) reciprocal lattice position. The spectral width of the magnetic scattering, indicating the rate of diffusion of the magnetic fluctuations, is observed to increase with temperature. The spatial range of the magnetic correlations is seen to decrease as the temperature is raised. The wavevector dependent magnetic susceptibility is found to follow a Curie-Weiss law near the (100) position, in agreement with theoretical predictions that presume the presence of well-defined local magnetic moments. (authors)