Comment on “Accurate determination of the magnetic anisotropy in cluster-assembled nanostructures” [Appl. Phys. Lett. 95, 062503 (2009)

Abstract

present a Stoner-Wohlfarth based analysis whereby they simultaneously“triple fit” the field-cooled (FC), zero-field cooled (ZFC),and high temperature magnetic response curves (m(H)at300K) of a magnetic nanogranular sample to determine, in aself-consistent way, the magnetic diameter distribution func-tion (or probability distribution function, PDF) and the effec-tive particle anisotropy. The authors show clearly how fits toboth the FC and the ZFC data are far more sensitive to varia-tions in the PDF than fits to m(H), concluding that only si-multaneous triple fitting leads to an unambiguous and highlyaccurate determination of the PDF and the particle anisot-ropy. The paper is, however, misleading with regard to theaccuracy of the common and widespread technique (see,e.g., Refs. 7 to 9 of Ref. 1) of individual m(H) fitting, using adiameter-weighted Langevin function, to determine PDFalone. Namely, in their discussion of Figure 1 in Ref. 1, theauthors state that the three calculated m(H) curves, corre-sponding to log-normal PDFs with mean diameters (D