Electrical transport properties and magnetic cluster glass behavior of Nd0.7Sr0.3MnO3 nanoparticles

Abstract

The transport and magnetic properties have been investigated in Nd0.7Sr0.3MnO3 nanoparticles prepared by the sol-gel method. The resistivity (ρ) increases with the decrease of the particle size due to the enhancement of the grain boundary effect. ρ(T) shows two distinct transitions for all the samples such as metal-insulator transition and transition due to the barrier caused by the grain boundary effect. The thermopower (S) is found to be negative and at high temperature S follows the adiabatic small polaron hopping theory. In the metallic region the spin wave contribution is found to be dominant in the temperature dependence of the thermopower. The magnetoresistance (MR) of the ultrafine particles increases with the decrease of particle size indicating substantial contribution from the grain boundaries. Spin polarized intergrain tunneling effect plays an important role in the MR of a smaller size particle, whereas in the case of samples of higher dimension spin fluctuation contributes predominantly. The field cooled (FC) and zero field cooled (ZFC) magnetizations display a paramagnetic-ferromagnetic transition at TC with a large magnetic irreversibility. The ZFC peak temperature TB and the irreversibility temperature (Tirr) are field dependent and decrease with the decrease of the particle dimension. Magnetic measurement indicates that particles are single domain with the particles of highest dimension lying in the multidomain region. A cluster glasslike behavior of the particles is revealed from the analysis of the dc and ac magnetization data.