Finite-size effects in ultrafast remagnetization dynamics of FePt

Abstract

We investigate the ultrafast magnetization dynamics of FePt in the L10 phase after an optical heating pulse, as used in heat assisted magnetic recording. We compare continuous and nanogranular thin films and emphasize the impact of the finite size on the remagnetization dynamics. The remagnetization speeds up significantly with increasing external magnetic field only for the continuous film, where domain wall motion governs the dynamics. The ultrafast remagnetization dynamics in the continuous film are only dominated by heat transport in the regime of high magnetic fields, whereas the timescale required for cooling is prevalent in the granular film for all magnetic field strengths. These findings highlight the necessary conditions for studying the intrinsic heat transport properties in magnetic materials.

Ultra-long spin relaxation in two-dimensional ferromagnet Cr2Ge2Te6 flake

“…For 3D metallic FM, the electron is itinerant and the motion of the electron in the 3D direction is not restricted, which means that it has a very high electron-phonon scattering rate and the coupling of the spin to electron system is strong. As a result, the demagnetization processes of 3D metal FM CT and the previously reported Co [43], Ni [30,44], Fe [45], FePt [40] all belong to type-I dynamics. For the 2D semiconductor FM such as CGT, the semiconductor properties make the Fermi level lack electrons, which leads to the weaker electron-spin coupling compared with the 3D metallic FM.…”

“…Magnetization dynamics is a macroscopic manifestation of the quantum phenomenon of exchange coupling dynamics between spins [19]. The spin dynamics is tightly related to both magnetic anisotropy and the thermal energy dissipation of the material [20,29,39,40]. Different from the 3D system, the 2D vdW magnets naturally have strong anisotropy for both magnetic interaction and the thermal energy dissipation rate due to the existence of vdW gap [3,41].…”

Spin stress contribution to the lattice dynamics of FePt

“…The laser spot size of approximately 1.6 mm by 1.3 mm (full width at half maximum) ensures that a homogeneously excited sample area is probed by the x-rays that have rhombical 0.3 mm–by–0.3 mm profile ( 39 ). The tr-MOKE setup ( 34 ) uses comparable excitation parameters. For experimental details, see Supplementary Materials.…”

“…3A and 2A at 85%. Because of the large out-of-plane anisotropy and the single-domain character of the grains (no domain wall propagation), we can use the tr-MOKE signal recorded with an external field of ±0.7 T as an estimation of the time-dependent average magnetization M(t) of the sample (34). The static magnetization curve M(T) of the granular FePt sample is depicted in Fig 4B . To relate the UXRD and tr-MOKE signal, we calculate an estimate for the spin contribution to the heat capacity (Fig.…”

Ultrafast terahertz magnetometry

“…refs. [36][37][38] and references therein). We note that, to the best of our knowledge, the direct measurement of such an acoustically driven magnetization dynamics on the ultrafast (sub-)picosecond timescale, and its co-existence with the direct laser-driven demagnetization via hot magnons, has not been reported before.…”