Coherent Spin Dynamics

Half metallic nature of manganites makes them technologically important materials for magnetic tunnel junctions and spin injection structures. The understanding of the magnetization dynamics in manganite thin film is important for the fastest switching operation of these devices. Several factors, such as the possible nornal modes and the damping of the coherent magnetization precesiion, play a crucial role in achieving reliable switching behavior.We investigate the dynamical magnetization response of epitixial manganite films to an ultrafast laser pulse. A pump beam (800 nm) excites magnetization precession, which is then monitored by a time-delayed probe beam (400 nm) by time-resolved magneto-optical Kerr effect (TR-MOKE) [2].

The time-domain spectra clearly display the oscillatory variation of the light intensity that passes through the analyzer. Since the polarization rotation is propotional to the normal component of M, the frequency of the oscillation correspond to the frequency of the magnetization precession. By performing a Fourier analysis of the time-domain spectra, we extract the field-dependent precession frequency.

The parameters of magnetic anisotropy are determined from the measured field dependence of the precession frequency. The dominant anisotropy contribution in the LCMO film grown on SrTiO3 (001) is the strain induced easy-plane anisotropy. The strain free films on NdGaO3 (110) exhibit a uniaxial in-plane anisotropy that results from the interface due to the tilting of the oxygen octahedra in NdGaO3. 

For LSMO film, the easy plane anisotropy is found in the tensile- strained film grown on SrTiO3 (001) substrate, whereas the compressive- strained film grown on LaAlO3 (100) substrate exhibits an easy normal-to-plane axis [2].

References:

1.  H. B. Zhao, K. J. Smith, Y. Fan, G. Lüpke, A. Bhattacharya, S. D. Bader, M. Warusawithana, X. Zhai, and J. N. Eckstein, Viscous spin exchange torque on precessional magnetization in (LaMnO3)2n/(SrMnO3)n superlattices, Phys. Rev. Lett. 100, 2008, pp. 117208-11.
2. D. Talbayev, H. Zhao, G. Lüpke, A. Venimadhav, and Qi Li, Photoinduced coherent magnetization precession in epitaxial La0.67Ca0.33MnO3 films, Phys. Rev. B 73, 2006, pp. 14417-1-8.
3. D. Talbayev, H. Zhao, G. Lüpke, J. Chen, and Qi Li,  Strain and anisotropy effects on spinwaves in epitaxial La0.67Sr0.33MnO3 films, Appl. Phys. Lett. 86, 2005, pp. 182501-3.