Evidence for magnetic phase separation inLa0.86Sr0.14Mn1−xCuxO3+δ manganites from NMR and magnetic measurements

Abstract

Polycrystalline La0.86Sr0.14Mn1−xCuxO3+δ (x = 0,0.05, 0.10, 0.15, 0.20) manganites were investigated by means of magnetic measurements and zero-field139La and 55Mn nuclear magnetic resonance (NMR) spectroscopy. Magnetization versus temperaturemeasurements revealed a paramagnetic to ferromagnetic transition in mostsamples, with lower Curie temperatures and broader transitions for samples withhigher Cu contents. The details of the magnetization measurements suggesteda phase-separated scenario, with ferromagnetic clusters embedded in anantiferromagnetic matrix, especially for the samples with large Cu contents(x = 0.15 and 0.20).Zero-field 139La NMR measurements confirmed this finding, since the spectral featuresremained almost unchanged for all Cu-doped samples, whereas the bulkmagnetization was drastically reduced with increasing Cu content.55Mn NMR spectra were again typical of ferromagnetic regions, with a broadening of theresonance line caused by the disorder introduced by the Cu doping. The results indicate acoexistence of different magnetic phases in the manganites studied, with the addition of Cucontributing to the weakening of the double-exchange interaction in most parts of thematerial.