Artificial material manipulation of magnetic anisotropy in FePt magnetic nanoparticles through application of hydrostatic pressure

摘要

The magnetostructural correlation in FePt nanoparticles (NPs) of various sizes was investigated as a function of pressure. An FePt NP size of approximately 2 nm corresponds to the critical size for the formation of the face-centered tetragonal (fct) structure in the FePt compound. FePt NPs with an initial size D0 of 2.6 nm, in which the fct structure was stably constructed, were investigated from the viewpoints of both their magnetic properties and crystal structure at pressures up to 26 kbar. The magnetic blocking temperature (TB) for D0 = 2.6 nm was reduced by contraction, which was contrary to the pressure-induced enhancement of TB for D0 = 2.0 nm. The pressure response observed for D0 = 2.6 nm rather than that for D0 = 2.0 nm is clearly a characteristic of FePt NPs with the fct structure. For D0 = 2.6 nm, pressure-induced suppression of the effective magnetic anisotropy occurred and, from the viewpoint of the structure, anisotropic contraction occurred on the unit-cell level. This study reveals that anisotropic unit-cell contraction in FePt NPs reduces the effective anisotropic energy K, and the magnetic nature of the NPs could be controlled by changing the contraction manner.