# Transverse spin relaxation and magnetic correlation in $Pr_{1-x}Ca_{x}MnO_{3}$ : influence of particle size variation and chemical doping

## TL;DR

This study investigates how particle size and chemical doping affect transverse spin relaxation and magnetic correlations in Pr-Ca manganites, revealing universal relaxation behavior and the persistence of charge ordering at nanoscale.

## Contribution

It demonstrates that magnetic correlations and charge ordering in Pr-Ca manganites persist and are even enhanced at nanoscale, with a universal scaling law for spin relaxation time.

## Key findings

- Spin-lattice relaxation dominated by thermally activated small polarons.
- Universal scaling of transverse spin relaxation time in the paramagnetic regime.
- Charge ordering survives and is enhanced at particle sizes down to 22 nm.

## Abstract

The short ranged magnetic correlations and dynamics of hole doped $Pr_{1-x}Ca_{x}MnO_{3}$ (0.33 < x < 0.5) of different crystallite sizes have been investigated using electron spin resonance spectroscopy (ESR). 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 typical activation energy of 20-50 meV. Irrespective of the crystallite size and dopant concentration, the transverse spin relaxation time ($t_{2}$) follows a universal scaling behaviour of the type $t_{2}$~($T/T_{0})^n$ in the paramagnetic regime, where $T_0$ and n are scaling parameters. Using the temperature dependence of $t_{2}$, we construct a phase diagram which shows that near half-doping, the magnetic correlations associated with charge ordering not just survives even down to the crystallite size of 22 nm, but is actually enhanced. We conclude that the eventual suppression of charge ordering with reduction in particle size is possibly more to do with greater influence of chemical disorder than any intrinsic effect.