Finite size effect on the magnetic glass

Abstract

The nature of glass formation and crystallization in structural glass is yet to be understood despite the intense studies of many decades. Analogous to the structural glasses, hindered first order magnetic transitions produce magnetic glasses, where the volume fraction of two phases having long range structural and magnetic order are frozen in time. Here, we have prepared Pr_0.5Ca_0.5Mn_0.975Al_0.025O₃ nanoparticles of different size as a case study and investigated the formation and stability of the magnetic glass state at the length scale of a few nanometers. We have observed a profound interplay between the glass state and sample size: stability of the glass state highly increases and scales linearly with decrease in the sample size. Smaller the particle size, slower is the crystallization rate. The crystallization occurs through both homogeneous and heterogeneous nucleation and is controlled by the surface to volume ratio of the particles. Our results emphasize on an important fact that glass transition is not a phase transition in actual sense, rather it is a kinetic phenomena. The length scale associated with different nucleation processes is an important length scale and it controls the glass dynamics. Besides, apart from the intrinsic metastability due to magnetic glass, we also distinguish a secondary source of relaxation, which is dominant at low magnetic fields, predominantly arising due to surface spin disorder.