A Small Angle Polarized Neutron Scattering Investigation of Magnetic Correlations in Nanocrystalline Fe₈₉Zr₇B₃Cu₁

Abstract

The technique of small angle neutron scattering (SANS) is ideally suited for determining the length scale of magnetic correlations in nanocrystalline materials. The additional use of polarized neutrons also allows for a clear separation between magnetic and non-magnetic scattering. The temperature dependence of the SANS cross-section from a two-phase alloy, consisting of both amorphous and nano-crystalline parts, Fe 89 Zr 7 B 3 Ctu,, has been measured in the temperature range from 293 to 500 K. The SANS measurements are accompanied by bulk magnetization and Mbssbauer transmission data. In this range of temperatures, the magnetic contrast between the nanocrystalline and amorphous phases, which are both magnetic, changes dramatically. This phase contrast increases up to 380 K, which is the proposed decoupling temperature for the inter-granular exchange stiffness. Above this temperature, the contrast levels off slowly, being totally dominated by the decreasing magnetization of the nanocrystalline phase.

Dipolar correlations in a nanocomposite: A neutron scattering study of NanopermFe89Zr7B3Cu

“…Close to saturation, at 0 H = 1.5 T, where the scattering originates dominantly from the spatial variation of the magnitude of the magnetization, the integrated total intensity increases up to T = 373 K, and it then enters a plateau region with no significant change up to 693 K, in agreement with the results of Ref. 74. This is well compatible with the expected temperature variation of ⌬M S which is shown sche-matically in Fig.…”

“…The average Fe particle size D = 12 nm was determined by x-ray diffraction and transmission electron microscopy. From Mössbauer experiments, 74 similar to the ones reported in Ref. 82, we have estimated the Curie temperature of the amorphous matrix phase at T C am Х 345 K and the crystalline volume fraction x C Х 40%.…”

“…The clover-leaf-shaped anisotropy remains clearly visible for temperatures up to T = 693 K, i.e., far above the Curie temperature T C am = 345 K of the amorphous matrix phase, which was determined from Mössbauer measurements. 74 Figure 6 represents a log-log plot of the temperature variation of the radially averaged difference SANS data at 290 mT. With increasing temperature the radially averaged data first take on a maximum at 323 K ͓not shown in Fig.…”