Project Details
Projekt
Using improper ferroelectricity and charge transfer in a novel approach to above room-temperature intrinsic ferrimagnetic multiferroics
Subject Area
Synthesis and Properties of Functional Materials
Term
from 2019 to 2024
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 429646908
Multiferroics with both ferroelectric and magnetic polarizations are rare due to the conflicting structural and electronic requirements of magnetism and ferroelectricity. Besides the fundamental interest in such materials, multiferroics have a tremendous application potential e.g. as sensors, actuators, and memory materials. However, up to now an applied multiferroic material, not to mention one with above room-temperature functionality, remains elusive. In this proposal we suggest a novel approach to obtain an above room-temperature multiferroic by using improper ferroelectricity and charge transfer in a ferrimagnetic double perovskite system. Perovskites ABO3 (A is a rare-earth (R) or alkaline-earth element and B is a transition metal) are known for A-site driven ferroelectricity and B-site driven magnetism as in the case of the up to now most famous multiferroic BiFeO3. Its low magnetization due to canted antiferromagnetic order along with the phase-instability of Bi-containing compounds in general keeps this compound away from practicability. Double perovskite (A2BB′O6) systems with two different transition metal cations at the B-site show a wide variety of physical properties including above room-temperature ferrimagnetism. So-called hybrid improper ferroelectricity describes a state where a suited distortion pattern in a ferromagnetic material creates a ferroelectric polarization. By engineering two nonpolar ferro- or ferrimagnetic materials within a superlattice, improper ferroelectricity can be evoked, making available a novel type of multiferroic material.In the first part of this project, we propose to investigate bulk and thin films of the newly discovered double perovskite system R2FeReO6 with a well above room-temperature ferrimagnetic ordering temperature, TC, of about 730 K and a large saturation magnetization, MS, of 1.7 µB/f.u. at room temperature for R = La. Subsequently, we will fabricate and investigate La2FeReO6/R2FeReO6 thin film superlattices, synthesized by stacking in a layer-by-layer growth mode, alternately La2FeReO6 and R2FeReO6 layers, where R is a rare-earth element other than La. The resulting A-site layering with La and R will produce antipolar motions of the La and R atoms in the perovskite lattice which will induce, in turn, sizable ferroelectric polarization. The cationic ordering in both the A-site and B-site are necessary for activating ferroelectricity and ferrimagnetism in this hybrid compound. The expected charge transfer from the Re site towards the Fe site will induce a significant charge difference at the two different B-sites promoting a high degree of B-site ordering. We will use state-of-the-art pulsed laser deposition to artificially tailor A- and B-site ordered LaRFeReO6 double perovskites as above room-temperature multiferroics. Substrate induced epitaxial strain and chemical strain due to various R ionic radii are additional degrees of freedom to be implemented to tailor the ferroic orders.
DFG Programme
Research Grants
International Connection
France
