In this paper, microstructure study of pinning sites of highly (0001) textured Sm(Co,Cu) 5 thin films was presented. Various types of pinning sites were identified, such as voids, grain/matrix boundaries (or crystalline/amorphous boundaries), grain boundaries between crystalline grains, and composition inhomogeneity in grains. One key finding of TEM elemental mapping was that Cu atoms were rich in the inner part of Sm(Co,Cu) 5 grains (defined by Sm and Co concentrations), instead of the outer part of grains, such as grain boundaries. Cu served as an alloying element in Sm(Co,Cu) 5 grains, not as a doping element to form Cu-rich grain boundaries. A model of Sm(Co,Cu) 5 films with lateral graded anisotropy due to composition/crystallization variation can explain the huge difference between the H C and H K.
Bibliographical noteFunding Information:
The authors thank the useful discussion with Dr. Yukiko Kubota, Dr. Ganping Ju, and Dr. Bin Lu, and the partial support from Seagate Technology and Information Storage Industry Consortium Extremely High Density Recording Program. Parts of this work were carried out in the Characterization Facility (Charfac), University of Minnesota, a member of the NSF-funded Materials Research Facilities Network (www.mrfn.org) via the NSF MRSEC program under Award No. DMR-0819885.