Raman spectroscopy of the Jahn–Teller phonons in a magnetic LaMnO3 thin film grown on KTaO3

Abstract

Bulk LaMnO3 is an A-type antiferromagnetic material in which the Jahn–Teller (JT) planes each have a ferromagnetic arrangement, but are stacked in antiparallel. Here, we report the growth of epitaxial LaMnO3 films on (001)-oriented cubic KTaO3 substrates in such a way that the JT plane is parallel to the nonmagnetic substrate. We verify the presence of the JT distortion and confirm the orientation of the plane by symmetry analysis with angle-resolved polarized Raman spectroscopy. The temperature evolution of the Raman spectra indicates that the B1g JT phonon softens below the magnetic transition temperature of ∼145 K, where ferro- or ferri-magnetism with magnetic easy axis along the out-of-plane direction is exhibited.

Theoretical Study of the Phonon and Electrical Conductivity Properties of Pure and Sr-Doped LaMnO3 Thin Films

“…It must be mentioned that γ is larger in the doped case compared to the undoped one for both cases-negative R < 0 and positive R > 0 (compare with Figure 4)-because the damping is proportional to R 2 ; see Equation (9). This behavior is due to the strong spin-phonon interaction R. An alternative means to observe the hardening of the phonon mode is the decrease in the Jahn-Teller distortion with increasing doping concentration x [13,36]. The reduction in the Jahn-Teller distortion in Sr-doped LMO has the same effect on the phonon energy as the change in the crystal symmetry due to the temperature-induced phase transition.…”

“…The phonon energy is reduced compared to the free thin film. The effects of the substrate-induced strain on the phonon modes in Sr-doped LMO thin films [12][13][14][15] will be considered in a future paper. The film thickness dependence of the phonon energy ω(N) for a Sr-doped LMO thin film, x = 0.1, is also observed using the model parameters 1, curve 2).…”

“…At 80 K, the lines of the A g symmetry are observed at 148, 210, 267, 295, 452 and 495 cm −1 and those of the B 1g symmetry at 197, 313, 436 and 606 cm −1 [8]. The Raman spectra of Sr-doped bulk LMO manganites are studied in [9][10][11], whereas those of pure and Sr-doped LMO thin films and nanoparticles are investigated in [12][13][14][15][16][17][18]. Recently, Helton et al [19] have studied the damping and softening of transverse acoustic phonons in La 0.7 Sr 0.3 MnO 3 .…”