Designing switchable polarization and magnetization at room temperature in an oxide

Abstract

Ferroelectric and ferromagnetic materials exhibit long-range order of atomic-scale electric or magnetic dipoles that can be switched by applying an appropriate electric or magnetic field, respectively. Both switching phenomena form the basis of non-volatile random access memory, but in the ferroelectric case, this involves destructive electrical reading and in the magnetic case, a high writing energy is required. In principle, low-power and high-density information storage that combines fast electrical writing and magnetic reading can be realized with magnetoelectric multiferroic materials. These materials not only simultaneously display ferroelectricity and ferromagnetism, but also enable magnetic moments to be induced by an external electric field, or electric polarization by a magnetic field. However, synthesizing bulk materials with both long-range orders at room temperature in a single crystalline structure is challenging because conventional ferroelectricity requires closed-shell d(0) or s(2) cations, whereas ferromagnetic order requires open-shell d(n) configurations with unpaired electrons. These opposing requirements pose considerable difficulties for atomic-scale design strategies such as magnetic ion substitution into ferroelectrics. One material that exhibits both ferroelectric and magnetic order is BiFeO3, but its cycloidal magnetic structure precludes bulk magnetization and linear magnetoelectric coupling. A solid solution of a ferroelectric and a spin-glass perovskite combines switchable polarization with glassy magnetization, although it lacks long-range magnetic order. Crystal engineering of a layered perovskite has recently resulted in room-temperature polar ferromagnets, but the electrical polarization has not been switchable. Here we combine ferroelectricity and ferromagnetism at room temperature in a bulk perovskite oxide, by constructing a percolating network of magnetic ions with strong superexchange interactions within a structural scaffold exhibiting polar lattice symmetries at a morphotropic phase boundary (the compositional boundary between two polar phases with different polarization directions, exemplified by the PbZrO3-PbTiO3 system) that both enhances polarization switching and permits canting of the ordered magnetic moments. We expect this strategy to allow the generation of a range of tunable multiferroic materials.

Structure Evolution and Multiferroic Properties in Cobalt Doped Bi4NdTi3Fe1-xCoxO15-Bi3NdTi2Fe1-xCoxO12-δ Intergrowth Aurivillius Compounds

“…The search for multiferroic materials combining electric and magnetic properties in a single phase has attracted a lot of attention in the perspective of future spintronic or magnetoelectronic devices123. Unfortunately, only a handful of single phase multiferroics have been discovered so far, and most of them are not suitable for practical applications at present, either because the room temperature polarization/magnetization is too small or their mutual coupling is too weak456.…”

Recent developments related to multifunctional ferroelectric for room-temperature applications

“…Although previous works have reported composite multiferroics at room temperature by multiphase mixtures of magnetic and ferroelectric materials [6], the magnetoelectric coupling effect will prevent complete switch of ferroelectricity. In a recent issue of Nature, researchers at the University of Liverpool, Trinity College Dublin, and West Virginia University reported tunable multiferroic materials at room temperature in a bulk perovskite oxide [1]. The authors constructed a percolating network of magnetic ions with strong superexchange interactions, and this network has a structural scaffold with polar lattice symmetries at a morphotropic phase boundary.…”

“…Recent publications have reported important approaches of bulk and nanostructure ferroelectric materials at room temperature [1][2][3][4][5]. For bulk and nanostructure ferroelectric materials, applications at room temperature are technical challenges in information storage and nanoelectronics.…”

“…For bulk and nanostructure ferroelectric materials, applications at room temperature are technical challenges in information storage and nanoelectronics. The reported approaches provide a few new directions for research on low-power [1] and high-density storage [2] of nonvolatile ferroelectric memories, multifunctional nanoelectronics [2][3][4], discovery of new physical phenomena [1][2][3], and energy conversion applications [5].…”

“…Recent publications have reported important approaches of bulk and nanostructure ferroelectric materials at room temperature [1][2][3][4][5] Magnetoelectric multiferroic materials enable fast electrical writing and magnetic reading, and can thus be applied to non-volatile random access memory. However, fast electrical writing and magnetic reading exist more difficulties in single crystalline structure bulk materials because ferroelectricity need closed-shell d 0 or s 2 cation and ferromagnetic need open-shell d n with unpaired electron.…”