MRSej, Vol. 6, No.1, pp.1-9, 2004

EFFECT OF DIAMAGNETIC DILUTION ON SPIN DYNAMICS IN MANGANITES

V.A. Atsarkin¹, V.V. Demidov¹, D.G. Gotovtsev¹, N.E. Noginova^1,2

¹ Institute of Radio Engineering and Electronics RAS, 125009 Moscow , Russia

² Norfolk State University, Norfolk, VA 23504, USA

In the magnetically diluted LaMn_xGa_1-xO₃ single crystals, the EPR spectra of the Mn ions (at 0.02 <=  x <= 1), as well as NMR and nuclear spin-lattice relaxation of ⁶⁹Ga and ⁷¹Ga nuclei have been investigated. The analysis of the EPR spectra enabled one to follow the exchange narrowing effect to the point of appearance of a single Lorentzian line at x  >=  0.2. The transition from the antiferromagnetic to ferromagnetic type of spin ordering is confirmed under condition of the diamagnetic dilution with Ga, starting from x  = 0.8. At x  = 0.1, unusual broadening and splitting of the EPR spectrum are found upon cooling; this can be assigned to the effect of thermally activated internal motion with characteristic energy E_a of about 50 meV. The study of nuclear spin-lattice relaxation was performed in the temperature range of 190-390 K. The obtained data support the existence of the internal motion with the same value of E_a . This motion can be attributed to thermally activated re-orientations of the e_g electron orbitals of the Mn³⁺ ions subjected to the Jahn-Teller effect.

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