Influence of the crystalline microstructure on the magnetic ordering of nanocrystalline chromium

The magnetic and structural properties of nanocrystalline chromium (n-Cr) were studied by neutron powder diffraction and by synchrotron radiation diffraction techniques. The nanocrystalline Cr is composed of small-sized particles with antiferromagnetic ordering, medium-sized particles with transverse spin density wave (SDW) ordering, and large-sized particles with the same magnetic ordering as bulk Cr. The critical size DC between the small and medium-sized crystallites is 18 + or - 2 nm. The alteration of the magnetic properties of n-Cr is due to microstrain fluctuations which are correlated with the crystallite sizes rather than to the crystallite size itself. The microstrain fluctuations increase the SDW modulation length up to large values (10.5 nm for n-Cr vs 7.8 nm for bulk Cr).