Electronic properties of La2−2xSr1+2xMn2O7 (x = 0.4 and 0.5) single crystals are studied by electron spin resonance (ESR) and spin-lattice relaxation time measurements. Spin susceptibility χ(T) determined from the ESR signal intensity and macroscopically measured static-susceptibility data are in good agreement, thus ESR detects all spin species in the system. In both compounds, the ESR spectra contain a single, nearly isotropic Lorentzian line associated with the exchange coupled Mn3+ and Mn4+ ions. For the x = 0.5 compound, the fingerprints of charge ordering (CO) transition at TCO = 226 K are detected. In addition, strongly anisotropic ferromagnetic resonance spectra are found in both materials, suggesting the presence of extrinsic ferromagnetic phases. For x = 0.4, the longitudinal relaxation time T1 and the transversal relaxation time T2 are equal around room temperature that is a sign of exchange narrowing. The T1/T2 ratio increases to about 5 approaching the Curie temperature TC = 126 K. No sign of critical speeding up of T1 is detected. Instead, the slowing down of the relaxation rate takes place and T1 is proportional to Tχ(T). This is attributed to the freezing of short-range magnetic correlations in the external field.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - Jun 27 2003|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics