Transverse spin relaxation and magnetic correlation in Pr1−x Ca x MnO3: Influence of particle size variation and chemical doping

Abstract

The short ranged magnetic correlations and dynamics of hole doped Pr1–xCaxMnO3 (0.33 < x < 0.5) of different crystallite sizes have been investigated using electron spin resonance spectroscopy. The major contribution to the temperature dependence of paramagnetic line-width is attributed to the spin-lattice relaxation dominated by thermally activated hopping of small polarons with the typical activation energy of 20–50 meV. Irrespective of the crystallite size and dopant concentration, the transverse spin relaxation time (t2) follows a universal scaling behaviour of the type t2∼(T/T0)n in the paramagnetic regime, where T0 and n are the scaling parameters. Using the temperature dependence of t2, we construct a phase diagram which shows that near half-doping, the magnetic correlations associated with charge ordering not only survives even down to the crystallite size of 22 nm but is also actually enhanced. We conclude that the eventual suppression of charge ordering with reduction in the particle size is possibly more to do with the greater influence of chemical disorder than any intrinsic effect.