Fig. 2. Phonon-selective control of ferromagnetism in YTiO₃.

a, Infrared optical spectrum of b-axis vibrational modes (black). The three phonons pumped in this experiment are shaded in red (4 THz), blue (9 THz) and yellow (17 THz). b, The eigen-displacements corresponding to the pumped vibrational modes in a: the low-frequency mode primarily involves antipolar motions of the Y ions, whereas the two higher-frequency modes mainly consist of displacements of the apical and equatorial oxygens, respectively, within the TiO₆ octahedral cage. c, Depiction of the experimental set-up for the time-resolved MOKE measurements. E_MIR, terahertz/mid-infrared pump; E_probe, 800 nm probe; B_ext., external magnetic field. d, Pump-induced changes of the MOKE angle (${\varphi }_{\mathrm{M}}=\frac{\varphi \left(+H\right)-\varphi \left(-H\right)}{2}$) for the three different phonon excitations. The black dotted line shows the pump pulse envelope.

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