Spin Dynamics and Internal Motion in Magnetically Dilute Manganites Probed by EPR.

EPR spectra of a series of single crystal samples of LaGa_{1 – x}Mn_xO₃ manganites were studied in a broad range of temperatures (20–300 K) and compositions (0.02 ≤ x ≤ 1). Evolution of the spectra under the action of exchange interactions of Mn³⁺ ions leads to the formation of a single Lorentzian line for x ≥ 0.2. The results confirm the transition from antiferromagnetic to ferromagnetic spin ordering during diamagnetic dilution of the manganite with gallium, beginning with x = 0.8. For x = 0.1, the EPR spectra exhibit an anomalous broadening and splitting on cooling of the samples, which is interpreted as manifestations of a thermoactivated internal motion with a characteristic energy of about 50 meV. The results are compared with published data on the nuclear spin–lattice relaxation of gallium. The model of thermoactivated reorientations of the electron orbitals of Mn³⁺ ions subject to the Jahn–Teller effect is discussed. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]