Influence of finite-size effects on the Curie temperature ofL10−FePt

Abstract

We employ an atomistic model using a nearest-neighbor Heisenberg Hamiltonian exchange to study computationally the dependence of the Curie temperature of L1 0 -FePt on finite-size and surface effects in heat-assisted magnetic recording (HAMR) media. We demonstrate the existence of a size threshold at 3.5 nm below which the impact of finite-size effects starts to permeate into the center of the grains and contributes to the reduction of the Curie temperature. We find a correlation between the Curie temperature and the percentage of atomistic bonds lost on the surface as a function of grain size, which can be extended to apply to not only L1 0 -FePt but also generic magnetic systems of any crystal structure. In a recording medium, the inevitable grain size dispersion leads to an irreducible contribution to the dispersion of the Curie temperature. Therefore, our paper gives insight into finite-size effects, which have been predicted to be a serious limitation of HAMR.

Size-dependent Magneto-catalytic Effect in Ferromagnetic Nanoparticles

“…cannot be directly adopted as direct evidence for the possibility of inducing MCE at a temperature lower than its bulk Curie point. As shown in Figure 2B, a short-range spin polarization still exists at the particle's surface, where the system size is close to the magnetic correlation length [15]. Since the catalytic reactions happen at localized active centers, it seems that the full-range MCE can never occur at NP with a considerably small size.…”

“…As shown in Figure 2A, the thermal demagnetization curves of the outer-most shell and the inner core in a 1 nm Ni NP have been separately simulated. It's not surprising that the effective magnetization of the atoms at the outer-most shell is quite lower than the atoms at the inner core due to the atomistic bond loss on the surface [15]. It seems like the surface atoms at the 1 nm Ni NP are more magnetically-disordered, and thus can quickly decrease into the PM phase.…”

“…can approach 20~30% of the bulk value in NPs around 1 nm. [14,15] These findings indicate that it might no longer be applicable to simply use the bulk critical point to describe the phase-transition induced phenomenon, such as heat-assisted magnetic recording [16] and the magneto-catalytic effect (MCE) [17].…”