College Park, Maryland      June 6 - 10 , 2004

M3-A4 (2:30 PM): SANS Investigation and Model Description of Micromagnetism in a nano-precipitated two-phase Alloy

W. Wagner, J. Kohlbrecher (Paul Scherrer Institut, 5232 Villigen-PSI, Switzerland)

Small-Angle Neutron Scattering (SANS) was applied to investigate the micromagnetic properties of an alloy with nanometer sized ferromagnetic clusters embedded in a nonmagnetic (or paramagnetic) crystalline bulk matrix. Such kind of structure establishes in the two-phase alloy of composition Cu-24at.%Ni-8at%Fe, upon annealing segregating precipitates of a ferromagnetic Fe/Ni-rich phase embedded in a paramagnetic Cu-rich matrix. The precipitate array is governed by a pronounced {100}<110> rolling texture in combination with a preferential pile-up along the <100> directions, resulting in a fourfold peak-structure in the two-dimensional, nuclear and magnetic SANS pattern.

For a detailed interpretation of the magnetic SANS pattern and their response to an external field, a computer-assisted model reconstruction was performed, considering a regular three-dimensional array of magnetic clusters with variable orientation of the magnetic alignment in a thermally activated environment. These simulations prove that the magnetic moments of the precipitates are tightly bound to the easy directions, i.e. to <100>. At zero field, they are randomly distributed to all possible easy axes, whereas an external field of intermediate strength switches them into the easy axes with field parallel component, before they are forced into field-parallel alignment by a very strong field. The data are interpreted in terms of a model balancing the magnetic anisotropy, magnetic coupling across the interfacial matrix, potential energy in an external field and thermal activation.

Back to the Program

Last modified 07-May-2004 by website owner: NCNR (attn: Bill Kamitakahara)