Controlling laser-induced magnetization reversal dynamics in a rare-earth iron garnet across the magnetization compensation point

Measurement of transient strain induced by two-photon excitation

“…This is verified by ellipsometry, which yields an optical penetration depth of 170 nm at λ NUV . For λ NIR ellipsometry only yields a lower bound for the penetration depth which is consistent with the literature value of 65 μm [26][27][28]. The intensity profiles for both excitation wavelengths are depicted true to scale in Fig.…”

“…Recent publications on ferrimagnetic garnets reported magnetization dynamics via thermally induced crystalline anisotropy modification [23,32,33], similar to previous work in antiferromagnets [34][35][36]. More specifically, optically excited coherent and incoherent phonons are reported to generate spin waves (SWs) [27,37,38]. A quadratic fluence dependence of the spin-wave amplitude was discovered in several garnets already with moderate fluences below 15 mJ/cm 2 [25,38].…”

“…A two-photon absorption coefficient of β YIG = 130 cm/GW was reported for undoped YIG at photon energies of (1.17 + 1.93) eV = 3.1 eV [58]. Mainly, a two-step process via the 6 A 1g ( 6 S) → 4 T 1g ( 4 G) and subsequent 4 T 1g ( 4 G) → 4 T 1g ( 4 P) Fe 3+ -ion transitions in YIG and Bi:YIG accounts for the two-photon absorption in both materials [27,59,60], i.e., the two-photon transition proceeds via real and short-lived levels. The bismuth substitution affects the electronic and optical properties of YIG, e.g., increasing spin-orbit coupling, absorption, and even second-harmonic generation (SHG) efficiency [39,61,62].…”

“…From this, we determine the two-photon absorption coefficient β ≈ 2 cm/GW for exciting Bi 1 Y 2 Fe 5 O 12 at 800 nm. We believe that our quantitative evaluation of the strain generated by two-photon absorption is particularly important for a full understanding of lightdriven spin manipulation in magnetic insulators [23,27,[32][33][34][35][36][37][38], but it has more general relevance for ultrafast science on supposedly nonabsorbing or transparent matter. The large peak intensities around 1 TW/cm 2 necessary to drive 0.1% strain can be achieved both by high pump fluences and short pulse durations.…”

“…Among the magnetic oxides, yttrium iron garnet (YIG) provides the lowest magnon * bargheer@uni-potsdam.de damping. Below the charge-transfer transitions identified with the band gap of YIG, there are weaker crystal-field d-d transitions down to about 800 nm [26,27]. A large magnetooptical contrast is achieved by bismuth substitution [28], which connects this workhorse of magnon spintronics [29,30] and spin caloritronics [31] to optomagnetism.…”