ON THE POSSIBILITY OF A 2-STATE MAGNETIC-STRUCTURE FOR NANOCRYSTALLINE CHROMIUM

Wide-angle neutron diffraction measurements taken at temperatures from 6 to 250 K indicate that the portion of a chromium sample with a mean grain size of 73 nm is antiferromagnetically ordered at temperatures below 100 K. The Neel temperature (about 120 +/- 10 K) for this nanocr ystalline sample is suppressed considerably below that of strain-free single-crystal chromium (311 K). Similar measurements of other samples indicate that the amount of antiferromagnetic order decreases with de creasing grain size. The grain size dependence of antiferromagnetic or der is discussed in the context of a two-state model consisting of ant iferromagnetically ordered cores surrounded by interfaces, which are n ot antiferromagnetically ordered.