¹³⁹La NMR detection of ferromagnetic clusters far above the Curie temperature in La₀.₇Ca₀.₃Fe₀.₀₉Mn₀.₉₁O₃ spin-glass manganite

Abstract

The dependence of the ¹³⁹La nuclear magnetic resonance (NMR) spin-echo signal on temperature and on the power of the applied radio-frequency pulse is investigated in zero applied magnetic field in La₀.₇Ca₀.₃Fe₀.₀₉Mn₀.₉₁O₃ (LCFMO) with Curie temperature (Tc) of about 125 K. Plots of the spin-echo signal versus the NMR pulse power reveal two maxima, out of which the highpower component is observed up to temperatures above Tc. It is also found that while the temperature dependence of the NMR signal amplitude follows the value of static magnetization M(T), the NMR frequency, which is related to the local field at La positions, decreases only slowly and the ¹³⁹La NMR signal is preserved at least to 220 K. These results confirm the existence of large ferromagnetic clusters with long life-times above Tc in LCFMO