Implications of Mn site hyperfine fields on CMR properties of manganites as studied by perturbed angular correlation spectroscopy

Abstract

Time differential perturbed angular correlation measurements in La_0.7Ca_0.3Mn_0.995Hf_0.005O₃ (LCMO) and La_0.7Sr_0.3Mn_0.995Hf_0.005O₃ (LSMO) using ¹⁸¹Hf/Ta probe nuclei reveal the presence of two distinct hyperfine components, identified with Mn⁴⁺ rich and deficient sites. The occurrence of hole rich and deficient sites in the paramagnetic (PM) state of the samples is mainly attributed to cationic inhomogenity. Effect of phase separation is seen across PM to ferromagnetic transition in LCMO, while it is absent in LSMO at the bulk Curie temperature. Signature for lattice distortion in Mn³⁺ rich zones is seen in the case of Ca-doped manganite, while such an effect is much smaller in the case of the Sr-doped system. The present atomic scale study thus reveals that the phase separation effects and Jahn-Teller distortions might be essential for doped manganites to exhibit Colossal magneto resistance effects.