Magnetic small-angle neutron scattering on bulk metallic glasses: A feasibility study for imaging displacement fields

Abstract

Magnetic-field-dependent small-angle neutron scattering (SANS) has been utilized to study the magnetic microstructure of bulk metallic glasses (BMGs). In particular, the magnetic scattering from soft magnetic Fe 70 Mo 5 Ni 5 P 12.5 B 2.5 C 5 and hard magnetic (Nd 60 Fe 30 Al 10 ) 92 Ni 8 alloys in the as-prepared, aged, and mechanically deformed state is compared. While the soft magnetic BMGs exhibit a large field-dependent SANS response with perturbations originating predominantly from spatially varying magnetic anisotropy fields, the SANS cross sections of the hard magnetic BMGs are only weakly dependent on the field, and their angular anisotropy indicates the presence of scattering contributions due to spatially dependent saturation magnetization. Moreover, we observe an unusual increase in the magnetization of the rare-earth-based alloy after deformation. Analysis of the SANS cross sections in terms of the correlation function of the spin misalignment reveals the existence of field-dependent anisotropic long-wavelength magnetization fluctuations on a scale of a few tens of nanometers. We also give a detailed account of how the SANS technique relates to unraveling displacement fields on a mesoscopic length scale in disordered magnetic materials.

Magnetic small-angle neutron scattering

“…In these materials, such as Pd-Fe-Mn, Cr-Fe, Au-Fe, Ni-Mn, Fe 3−x Al x , a-(Fe 1−x Mn x ) 75 P 16 B 6 Al 3 , and a-Fe-Zr, a paramagnet-to-FM transition on cooling is followed by a transition to a spin-glass, i.e., from an ordered to a glassy state (Aeppli et al, 1983;Garcia-Calderón et al, 2005;Rhyne and Fish, 1985;Shapiro et al, 1980). SANS has been used for decades to probe magnetic ordering and correlation lengths in such alloys (Mettus et al, 2017), which have proven challenging to understand. As discussed in a-Fe 1−x Zr x , nanoscale magnetic inhomogeneity is common to essentially all models, where FM order coexists with spin-glass regions (Garcia-Calderón et al, 2005).…”

Evidence for the formation of nanoprecipitates with magnetically disordered regions in bulk Ni50Mn45In5 Heusler alloys

“…where j 0 (x) = sin(x)/x denotes the zeroth-order spherical Bessel function. The correlation function C(r) and the corresponding distance distribution function p(r) = r 2 C(r) can be extracted by either a direct [27][28][29][30] or an indirect [31][32][33][34][35][36] Fourier transform of d +− /d . Figure 6(b) shows the computed p(r).…”

Anisometric mesoscale nuclear and magnetic texture in sintered Nd-Fe-B magnets

“…Using the two-dimensional d M /d , the normalized magnetic correlation function c(y, z) can be numerically computed according to [53,54]…”