Nonclassical magnetic dynamics and negative exchange bias in Nd0.5Sr0.5MnO3 films

Abstract

The amorphous, nanoclustered, and self-organizing bilayered Nd Sr MnO 0.5 0.5 3 films have been prepared by a rf-magnetron sputtering. The amorphous film turn out to be a typical paramagnet with a freely moving of the individual Mn spins, the magnetic properties of which are well described by the Curie-Weiss approximation. The nanoclustered film manifests the magnetic properties mimic to the superparamagnetic particles with a nonclassical magnetic dynamics. Taking into account the unique shape of the hysteresis loops, which have hysteretic lobes at high magnetic field but are nonhysteretic as the field crosses zero, we suggest that each particle (nanocluster) is the closure magnetic domain (or magnetic vortex) rather than the single one. At the same time, the blocked to unblocked transition was observed with increasing temperature similar to the usual superparamagnet. The self-organizing bilayered film demonstrates a negative exchange bias, which is typical for the ferromagnet/antiferromagnet hybrid system in spite of that both layers in our case have a ferromagnetic origin. The magnetic properties of the films are discussed in detail on the base of modern theoretical models.

Origin of an enhanced colossal magnetoresistance effect in epitaxial Nd0.52Sr0.48MnO3 thin films

“…Therefore, one can conclude that all deposited films have a homogeneous microstructure without the intermediate layer [7] and the column-like texture [8][9][10]. On the other hand, the lattice mismatch between the film and the substrate ( 2%) leads to a biaxial compressive in-plane and a tensile out-of-plane strains.…”

Evidence of non-Dzyaloshinskii–Moriya ferromagnetism in epitaxial BiFeO3 films

“…This expression was obtained for an interacting SPM phase, which includes a strong dipolar interaction among SPM clusters. 17,18,25,26 Based on an analysis of the M͑T͒ and M͑H͒ dependences, one can, therefore, conclude that these BFO films can be regarded as a magnetic phase separated system consisting of a G-type AFM matrix and FM inclusions of non-DM-like origin. These inclusions are formed because of an oxygen deficiency 5 which appears in certain local regions of the film owing to crystal lattice imperfection or overstrain.…”

“…The observed magnetic field dependence of eff is governed by a possible dipolar interaction between SPM clusters. 17,18 Taking the magnetic moment of Fe 3+ to be ϳ6 B / Fe and assuming a spherical shape for the SPM clusters with a volume of D 3 / 6, their average diameter is estimated to be D ϳ 7.3, 4.33 and 3.5 nm for magnetic fields of 0.1, 0.5 and 1.0 T, respectively. In principle, these values are quite reasonable and indicate that an additional FM phase exists in the film in the form of SPM clusters.…”