Effects of annealing on the magnetic and structural properties of FePt nanoparticles prepared by chemical synthesis

Spontaneous oxidation of disordered fcc FePt nanoparticles

“…4,6,7 Due to the reported M s values that are much lower than expected for a fcc FePt bulk at 5 K, it is attributed to the presence of the nonmagnetic Fe shell. Nevertheless, the mechanism by which M s is too low is not completely understood.…”

“…1, we observe that M s at 5 K is about a factor 8 smaller for the FePt NPs and at RT the magnetization at 50 kOe is about 1 emu/ g. Similar very low values of M s have been also reported for "as prepared" FePt NPs. [3][4][5] In the case of iron oxide NPs, it is usually reported that the values of M s are smaller than the bulk values 17,18 and the behavior follows that the smaller the size is, the smaller the M s . Magnetite NPs synthesized by high temperature decomposition of organic precursors with diameters ranging from 5.7 to 11 nm have M s values at 5 K close to those reported for bulk Fe 3 O 4 ; at RT, M s slightly decreases as the particle diameter decreases.…”

“…Recent works [3][4][5][6][7] have proved that the synthesis by a high-boiling coordinating solvent method gives place to a core-shell structure of the FePt NPs. Delalande et al 3 have proposed that FePt NPs have a Pt rich core and a Fe rich shell due to the different nucleation kinetics of Pt and Fe: Pt nucleates faster and easier than Fe.…”

“…Möess-bauer results recently published indicate that the shell is made up of distorted spinel-type iron oxides like maghemite ͑␥-Fe 2 O 3 ͒. 4 There exist also previous works that report on this core-shell structure of FePt nanoparticles. Wu et al 5 ascribe the low magnetization state of the as-made FePt NPs to the formation of a nonmagnetic shell ͑of about 0.5 nm͒ arising from the bonding of the acid group of oleic acid to Fe.…”

L 1 FePt-oxide columnar perpendicular media with high coercivity and small grain size

“…[3][4][5][6] Various materials have been added to the FePt layer to magnetically decouple the FePt grains. 7,8 In situ heating, 9 postannealing, 10 and atomic sputtering of Fe/ Pt multilayers 11 have been used to transform FePt from the fcc structure to the L1 0 ordered structure, since FePt alloy sputtered at room temperature has the fcc structure with ͑111͒ texture. In this paper, we report the results of our study on fabricating FePt recording media.…”