Electronic properties of 4-nm FePt particles

Space‐Confined Formation of FePt Nanoparticles in Ordered Mesoporous Silica SBA‐15

“…[28] The coercivity of composites reduced at 750°C is also lower as compared to isolated FePt nanoparticles but comparable to FePt silica coreshell structures reported by Yu et al [29] For samples synthesized by the oxidation method, the magnetization at H = 4 kOe is significantly lower at 300 K than at 2 K, while for samples prepared via direct reduction the temperature dependence of the magnetization was not pronounced. and B h = 31.2(1) T at 4.2 K. In contrast to the line broadening effects between 250 and 185 K observed for 4 nm FePt particles, [30,31] we already observe hyperfine field splitting at room temperature, in agreement with the magnetization data taken at 300 K. The observed hyperfine field slightly increases from room temperature to 4.2 K with values similar to those for the 4 nm FePt nanoparticles. [30,31] Summarizing, we have demonstrated efficient generation of FePt nanoparticles in an ordered mesoporous oxide and subsequent transformation of the cubic FePt nanoparticles into fct-FePt.…”

“…and B h = 31.2(1) T at 4.2 K. In contrast to the line broadening effects between 250 and 185 K observed for 4 nm FePt particles, [30,31] we already observe hyperfine field splitting at room temperature, in agreement with the magnetization data taken at 300 K. The observed hyperfine field slightly increases from room temperature to 4.2 K with values similar to those for the 4 nm FePt nanoparticles. [30,31] Summarizing, we have demonstrated efficient generation of FePt nanoparticles in an ordered mesoporous oxide and subsequent transformation of the cubic FePt nanoparticles into fct-FePt. The mesoporous matrix with well defined pore size COMMUNICATION 3024 www.advmat.de allows to control the particle diameter and hinders sintering and aggregation during the thermally induced phase transformation.…”

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.…”

“…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.…”

“…3͒. Due to the steep decrease of magnetization at zero external field, the magnetic curve of batch IIa looks like the sum of two non-interacting magnetic phases: a hard and a soft phase; however, the kink at around zero field is a signal that either there are NPs still not blocked at 5 K ͑as proposed by Stahl et al 7 ͒ or the surface of the NPs oxidizes. As can be seen in Fig.…”