A small angle neutron scattering and Mossbauer spectrometry study of magnetic structures in nanocrystalline Ni3Fe

Results are reported from small angle neutron scattering and Mossbauer spec trometry measurements on nanocrystalline Ni3Fe. The nanocrystalline materia ls were prepared by mechanical attrition and studied in the as-milled state , after annealing at 265 degrees C to relieve internal stress, and after an nealing 600 degrees C to prepare a control sample comprising large crystals . The small angle neutron scattering (SANS) measurements were performed for a range of applied magnetic fields. Small differences were found in how th e different samples reached magnetic saturation. From the SANS data obtaine d at magnetic saturation, we found little difference in the nuclear scatter ing of the as-milled material and the material annealed at 265 degrees C. R eductions in nuclear scattering and magnetic scattering were observed for t he control sample, and this was interpreted as grain growth. The material a nnealed at 265 degrees C also showed a reduction in magnetic SANS compared to the as-milled material. This was interpreted as an increase in magnetic moments of atoms at the grain boundaries after a low temperature annealing. Both Mossbauer spectroscopy and small angle neutron scattering showed an i ncrease in the grain boundary magnetic moments after the 265 degrees C anne aling (0.2 and 0.4 mB/atom, respectively), even though there was little cha nge in the grain boundary atomic density. (C) 1999 American Institute of Ph ysics. [S0021-8979(99)07610-0].