Photoinduced coherent magnetization precession in epitaxial ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ films

Optically excited uniform magnetization precession in the ferromagnetic state of ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ films grown on different substrates is investigated by the time-resolved magneto-optic Kerr effect. The parameters of magnetic anisotropy are determined from the measured field dependence of the precession frequency. The dominant anisotropy contribution in the film grown on ${\mathrm{SrTiO}}_3\left(001\right)$ is the strain-induced easy-plane anisotropy. In the strain-free films on ${\mathrm{NdGaO}}_3\left(110\right)$, we discover a uniaxial in-plane anisotropy that results from the interface due to the tilting of the oxygen octahedra in ${\mathrm{NdGaO}}_3$.

Figure 1

(Color online) (a) Geometry of the pump-probe measurement with applied magnetic field. (b) Magnetization precession as measured by TR-MOKE in the 60-nm LCMO/NGO film at $T=20\mathrm{K}$ and $\alpha =45°$, with $\alpha$ defined in (a).

Figure 2

(Color online) Field dependence of the precession frequency in LCMO/STO. Solid lines are calculated using the expressions given in the Appendix with effective fields given in Table and a $g$ factor of 1.98. (a) Applied magnetic field is in plane. The $\alpha =0°$ and $\alpha =45°$ orientations correspond to the field along the in-plane tetragonal easy axis and along the in-plane tetragonal hard axis, respectively. $\alpha$ is defined in Fig. 1. (b) Applied magnetic field is almost normal to the film and lies in the $Y\text{−}Z$ plane, with $Y$ being the tetragonal easy axis.

Figure 3

(Color online) Field dependence of the precession frequency in LCMO/NGO, in the $100{\mathrm{nm}}^{*}$ sample in Table . Solid lines are calculated using the expressions given in the Appendix with effective fields given in Table and a $g$ factor of 1.98. (a) Applied magnetic field is in plane. The $\alpha =45°$, $\alpha =90°$, and $\alpha =135°$ orientations correspond to the field along the in-plane uniaxial easy axis, at $45°$ to the easy axis, and along the in-plane uniaxial hard axis, respectively. $\alpha$ is defined in Fig. 1. (b) Applied magnetic field is almost normal to the film and lies in the $Y\text{−}Z$ plane, with $Y$ being the uniaxial easy axis.

Figure 4

(Color online) Field dependence of precession frequency in LCMO/NGO, in the 60, 100, and $150\mathrm{nm}$ samples in Table . Solid lines are calculated using the expressions given in the Appendix with effective fields given in Table and a $g$ factor of 1.98. Applied magnetic field is in plane. In each panel the $\alpha =45°$, $\alpha =90°$, and $\alpha =135°$ orientations correspond to the field along the in-plane uniaxial easy axis, at $45°$ to the easy axis, and along the in-plane uniaxial hard axis, respectively. $\alpha$ is defined in Fig. 1.