Abstract
Magnetic properties of polycrystalline La0.81Sr0.19Mn0.9Fe0.1−xZnxO3 (x = 0, 0.05) have been investigated by means of electron spin resonance, magnetic susceptibility, and Mössbauer measurements. Both samples show a clear ferromagnetic transition. The Curie temperature TC decreases on increasing Fe content (x = 0.05—TC = 222 K; x = 0—TC = 148 K). Mössbauer studies indicate that Fe in these compounds is in the trivalent high-spin state. The temperature evolution of the Mössbauer spectra at low temperatures (T < TC) is typical for ferromagnetic clusters with a wide distribution in size and magnetic correlation length. The inverse susceptibility of all the samples deviates from the Curie–Weiss law above TC, indicating the presence of fluctuations on approaching magnetic order. An anomalous downturn of the inverse susceptibility for x = 0.05 significantly above TC and the concomitant observation of ferromagnetic resonance signals coexisting with the paramagnetic resonance up to approximately room temperature, is caused by a Griffiths-like behavior. This regime is characterized by the coexistence of ferromagnetic entities within the globally paramagnetic phase.
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