Mn_0.7Fe_2.3O₄ Nanoplatelets Embedded in BaTiO₃ Perovskite Thin Films for Multifunctional Composite Barriers

Multifunctional materials having the ability to respond to various external fields are tremendously sought, not only for their potential use as sensing components for devices but also because they provide an elegant way to optimize materials usage. However, multifunctional single-phase materials are scarce, and one approach to overcome this problem is to build artificial compounds combining different properties. This is a challenging materials science task, especially when two-dimensional structures are considered. In this paper, we report on the successful realization of multifunctional systems consisting of ferrimagnetic Mn0.7Fe2.3O4 spinel platelets, of controlled sizes and nanometric thicknesses, embedded in an epitaxial ferroelectric BaTiO3 perovskite thin film. The embedded platelets experience a much higher isostatic strain than that obtained for single layers. We successfully achieved nanometer-thick composite layers, with identical composition, having either in-plane or out-of-plane electric polarization orientations. The optimal samples combine several functionalities: (i) the magnetoelectric nature of the full oxide artificial structures is confirmed, (ii) semiconducting diode behaviors are obtained when contacted with a metal electrode, and (iii) marked (eightfold) electro-resistance transport properties with respect to the electric polarization orientation are revealed. The embedded platelets configuration enhances significantly interface and two-dimensional effects and is thus believed of high interest to realize functional device structures.