  All-optical helicity-dependent magnetization switching (AO-HDS) is the
quickest deterministic technique for data storage by solely using ultrashort
laser pulses. Granular high data density magnetic storage media developed for
heat-assisted magnetic recording (HAMR) provide an ideal playground to
investigate the interplay of effects leading to magnetization switching. In the
latest perception, we identify two effects, the magnetic circular dichroism
(MCD) and the inverse Faraday effect (IFE), as the forces driving the switching
process. During photon absorption, which leads to a rapid temperature rise and
thus to magnetization quenching, the MCD ensures two distinct electron
temperatures due to helicity-dependent absorption. This effect already holds a
nonvanishing probability for magnetization switching. At the same time, the IFE
induces a magnetic moment within the material, enhancing the switching
probability. We present AO-HDS experiments using ultrashort laser pulses
($\lesssim 200\,\mathrm{fs}$) in the near-infrared range from
$800\,\mathrm{nm}$ to $1500\,\mathrm{nm}$. The experiments demonstrate a strong
dependence of the switching efficiency on the absorbed energy density,
elevating the electron temperature in the vicinity of the Curie point, allowing
for the IFE to take full effect, inducing a magnetic moment for deterministic
switching in the quenched magnetization state. While we do not observe an
enhanced switching due to an increased MCD, a higher induced magnetization
usually improves the switching rate if the electron temperature reaches the
transition temperature vicinity. Therefore, we conclude that the magnetic
moment generated by the IFE is crucial for the switching efficiency and the
distinct deterministic character of the switching process. Laser pulses with a
higher absorption induce a higher magnetic moment and switch magnetization at
lower fluences.
