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High-field ESR on the spin dynamics in La1-xSrxMnO3



Physical properties of doped manganites remain the subject of intensive investigations. Initiated by the observation of colossal magnetoresistance at the metal-to-insulator transition, the research efforts have been extended to the properties of different phases ranging from a ferromagnetic (FM) metal to an antiferromagnetic (AFM) insulator.
The parent compound, LaMnO3, reveal antiferromagnetically-ordered structure at low temperatures, which is transformed to a canted magnetic structure for 0 < x < 10%. For higher doping levels (10% = x = 15%) La1-xSrxMnO3 is a ferromagnetic insulator in the magnetically-ordered state. Finally, for x > 15% the ferromagnetic and metallic state is observed.

References:

  1. Spin dynamics in La1-xSrxMnO3 (x = 0.175) investigated by high-field ESR spectroscopy, D. Ivannikov, M. Biberacher, H.-A. Krug von Nidda, A. Pimenov, A. Loidl, A. A. Mukhin, and A. M. Balbashov, Phys. Rev. B 65, 214422 (2002).
  2. High-field AFMR in single-crystalline La0.95Sr0.05MnO3: Experimental evidence for the existence of a canted magnetic structure, A. Pimenov, M. Biberacher, D. Ivannikov, A. Loidl, V. Yu. Ivanov, A. A. Mukhin, and A. M. Balbashov, Phys. Rev. B 62, 5685 (2000).
  3. Antiferromagnetic Resonance in the Canted Phase of La1-xSrxMnO3: Experimental Evidence Against Electronic Phase Separation, A. A. Mukhin, V. Yu. Ivanov, V. D. Travkin, A. Pimenov, A. Loidl, and A. M. Balbashov, Europhys. Lett. 49, 514 (2000).



LaMnO3 - Antiferromagnetic Insulator

Frequency-dependent transmittance of LaMnO3 single crystal in zero external magnetic field (upper panel) and in B = 3 T (lower panel). The splitting of the AFMR mode is clearly seen. Symbols - experiment, lines - model calculation using one (B=0) or two (B=3 T) Lorentzians to account for the magnetic absorption. The interference patterns are due to the reflectance from the sample edges. Ref. [1]. antiferromagnetic insulator


La0.95Sr0.05MnO3 - Canted Antiferromagnet

canted antiferromagnet Magnetic-field dependence of the submillimeter transmittance of La0.95Sr0.05MnO3 untwinned crystal for two different orientations. Apparent disappearance of the ESR-line in the upper panel at low temperatures is due to different excitation conditions for this geometry. In fact, a high-frequency AFMR-mode (~400 GHz) is observed. Ref. [1,2].
Magnetic field-dependence of the resonance frequencies of the AFMR lines in La0.95Sr0.05MnO3 at low temperatures. Solid lines were calculated according to the model of the canted magnetic structure. These results cannot be explained on the basis of the phase-separation scenario. Ref. [1,2]. canted antiferromagnet


La0.875Sr0.125MnO3 - Ferromagnetic Insulator

ferromagnetic insulator

Magnetic-field (left) and frequency (right) dependence of the transmittance of La0.875Sr0.125MnO3 crystal. The observed complicated structure corresponds to a single line of the ferromagnetic resonance (FMR). Symbols - experiment. Solid lines were calculated assuming a single FMR mode with the linewidth being the only free parameter (resonance frequency is fixed by g=2, and the intensity - by the static magnetization value). Ref. [1].
ferromagnetic insulator


La0.825Sr0.175MnO3 - Ferromagnetic Metal

ferromagnetic metal High-field ESR spectra of La0.825Sr0.175MnO3 in the reflectance geometry. The ferromagnetic resonance (FMR) and antiresonance (FMAR) modes are marked by arrows. Symbols - experiment, lines - fit. The line splitting of the FMR mode is due to the anisotropy of the crystal field below the rhombohedral-to-orthorhombic phase transition at TRO. The inset shows the temperature dependence of the resonance-line positions. Ref. [1].



For further information contact: peter.lunkenheimer@physik.uni-augsburg.de