Nanoscale Confinement Enhances Ultrafast Demagnetization
Yoav William Windsor, Tobias Lojewski, Moumita Kundu, Klaus Sokolowski‐Tinten, Nico Rothenbach, Andrea Eschenlohr, Markus Ernst Gruner, Katharina Ollefs, Carolin Schmitz‐Antoniak, Soma Salamon, Daniela Zahn, Laurenz Rettig, Christian Schüßler‐Langeheine, Niko Pontius, Renkai Li, Mianzhen Mo, Suji Park, Xiaoshe Shen, Stephen Weathersby, Xijie Wang, Rossitza Pentcheva, Heiko Wende, Ulrich Nowak, Uwe BovensiepenABSTRACT
Nanoscale miniaturization has revolutionized the field of spintronics by enabling exponential growth in areal bit density. A similar leap is also expected in device speeds through successfully harnessing femtosecond magnetization dynamics. However, combining this with the miniaturization of realistic devices is challenging. To address this, we studied the effect of dimensional confinement on the femtosecond demagnetization of Fe. By gradually increasing the level of confinement while keeping excitation conditions constant, we found that Fe layers thinner than 10 nm exhibit enlarged demagnetization amplitudes, reaching a ∼75% increase at 2 nm. By combining ultrafast experiments sensitive to the spins, the charge carriers, and the phonons, we establish that this finite‐size effect is magnetic in origin and is not phonon‐driven. With the support of ab initio calculations and atomistic spin dynamics simulations, we identify the enhancement effect as due to local weakening of spin order at the Fe's interface, which becomes significant upon increased confinement.