Two states of magnetic frustration in La0.7Sr0.3MnO3 amorphous films with fractal structures: New knowledge about clusters and cluster ensembles

Abstract

In amorphous La0.7Sr0.3MnO3 films with a fractal structure, two states of magnetic frustration were found, which are the characteristic of cluster spin glass (CSG) and spin glass (SG) states and are associated with the presence of competing, FM and AFM, magnetic interactions, and the geometry of fractal formations. A high density of clusters in them provides effective magnetic interactions of magnetic moments without the participation of free charge carriers. It has been established that the formation of CSG begins with the transition of the central parts of the clusters to the FM state (at T < 98 K) and ends with the formation of the AFM order in the peripheral areas of the clusters, at T < 64 K. Increasing the field to H = 1.2 kOe, which stimulates AFM ordering of peripheral areas, strengthens the state of the cluster glass. A further decrease in temperature (T < 26 ) and an increase in the field (H > 2.5 kOe) causes the transition of peripheral areas from the AFM to the SG state. A phenomenological description of the frustration process is made. The dependences of the order parameter and barrier height on temperature and magnetic field have been studied. The consequences of the CSG ⇒ SG phase transition for the magnetism of the samples and the direct influence of the external field on their magnetic structure are discussed.