EMR STUDY OF THIN La_(0.7)Ca_(0.3)MnO_3 FILMS EPITAXIALLY GROWN ON SrTiO_3

摘要

The electron magnetic resonance (EMR) study was done at temperatures 130 ≤ T ≤ 340 K for two La_(0.7)Ca_(0.3)MnO_3 films -22 nm thickness, Curie temperature T_C = 254 K and 70 nm, T_C = 263 K - epitaxially grown on SrTiO_3 under identical conditions using pulsed laser deposition,. At T < T_C both films showed a strong angular dependence of EMR lines due to magnetocrystalline and shape anisotropies. At increasing T, the effective anisotropy decreases and lines converged at T ～ 1.2T_C . The EMR line widths demonstrated gradual narrowing at T increase, having a spike-like feature in the vicinity of T_C. On the other hand, EMR spectra of these two films revealed significant differences. The 22 nm film showed enormously broad lines in both orientations. Within the certain temperature range, additional lines in low and high fields were clearly observed. Spin wave resonance (SWR) modes were detected in spectra of the 70 nm film at 230 ≤ T ≤ 280 K. The peculiarities observed may originate from the different structural states of these films: the 70 nm film is a quasi-relaxed and bulk-like one while the 22 nm film has an additional strained phases distinguishing in magnetic characteristics.