Figure 1

Time dependence of the pump-induced transient reflectivity $\Delta R/R$ in the (a) paramagnetic and (b) helimagnetic states. The temperature dependence of the maximum $\Delta R/R$ is plotted in (c) for several applied magnetic fields. Also shown in (c) are illustrations of the helical (left) and conical (right) spin structures present in the low temperature magnetic phases for $H<H_c$ [see phase diagram in Fig. 2e].Reuse & Permissions

Figure 2

(a)–(c) Time dependence of the pump-induced change in Kerr rotation $\Delta {\theta }_{\mathrm{K}}$ as a function of temperature for several applied magnetic fields. (d) $\Delta {\theta }_{\mathrm{K}}$ as a function of magnetic field at $T=15\mathrm{K}$. Curves are offset for clarity. Also shown is a schematic phase diagram (e), adapted from Ref. 7, with red arrows illustrating the temperature and field scans used in (a)–(d).Reuse & Permissions

Figure 3

(a) Exemplary $\Delta {\theta }_{\mathrm{K}}$ oscillation data (blue circles) and fit (solid black line) using the model described in the text and fitting procedure detailed in the Supplemental Material [21]. The fit is decomposed into an exponential term (dashed green line) and an oscillatory term (dotted red line). The fitting function uses a single time constant ${\tau }_{\mathrm{K}}$ for all terms which is plotted in panel (b) as a function of temperature for different magnetic fields. The solid line is a guide to the eye. The inset to (b) compares ${\tau }_{\mathrm{K}}$ to the reflectivity decay time, ${\tau }_R$, both averaged over all fields, with error bars showing the standard deviation. Panels (c) and (d) show the reduced magnetization oscillation frequency for field scans and temperature scans, respectively. The values of $H_c$ are extracted from ac susceptibility measurements [29], and the values and $T_c$ are deduced from the Kerr measurements as described in the text. The dotted and solid lines in (c) and (d) are derived from the theory as described in the main text. Statistical error from the fitting is smaller than the data markers in (b)–(d).Reuse & Permissions