Magnetic-moment distribution in Ni_0.97Ru_0.03 alloy

Abstract

Using polarized neutrons, the full three-dimensional magnetic-structure amplitudes in Ni_0.97Ru_0.03 single crystals were measured up to (sinθ)/λ=0.9 Å^-1. The form-factor analysis yields a local moment on the Ni atom of (0.582±0.005)μ_B and one on the Ru atom of (-3.08±0.33)μ_B. Also, the fractional population of the moment in the T_2g orbital is found to be 0.84±0.01, indicating that the moment is more asymmetric than in pure Ni, in contrast to what others have observed in nickel-based alloys with 3d impurities. Moment density maps in various portions of the Wigner-Seitz (WS) cell were obtained. Unlike the case of Ni, we find on the surface of the WS cell small islands of negative density around 1/20 0, for instance, and fairly large islands of positive density around 1/4 1/4 0, for example. A net small positive diffuse moment density of 0.0015μ_B/ų is obtained by averaging over all the faces of the WS cell. The observed asymmetry in these density maps confirms the conclusion drawn from the form-factor analysis. The sign and magnitude of the Ru moment, together with the extensive perturbations introduced by it, both on the host local moment and the diffuse moment, seem to point to the existence of a virtual bound state very near the Fermi energy and support a similar conclusion drawn from resistivity and thermoelectric-power data.