Magnetic control of large room-temperature polarization

A novel perovskite oxide chemically designed to show multiferroic phase boundary with room-temperature magnetoelectricity

There is a growing activity in the search of novel single-phase multiferroics that could finally provide distinctive magnetoelectric responses at room temperature, for they would enable a range of potentially disruptive technologies, making use of the ability of controlling polarization with a magnetic field or magnetism with an electric one (for example, voltage-tunable spintronic devices, uncooled magnetic sensors and the long-searched magnetoelectric memory). A very promising novel material concept could be to make use of phase-change phenomena at structural instabilities of a multiferroic state. Indeed, large phase-change magnetoelectric response has been anticipated by a first-principles investigation of the perovskite BiFeO₃–BiCoO₃ solid solution, specifically at its morphotropic phase boundary between multiferroic polymorphs of rhombohedral and tetragonal symmetries. Here, we report a novel perovskite oxide that belongs to the BiFeO₃–BiMnO₃–PbTiO₃ ternary system, chemically designed to present such multiferroic phase boundary with enhanced ferroelectricity and canted ferromagnetism, which shows distinctive room-temperature magnetoelectric responses.

Structural change at multiferroic phase boundary is anticipated to have an associated large magnetoelectric response, which yet awaits to be evidenced. Here, Fernández-Posada et al. report electric field-induced phase change for a BiFeO₃–BiMnO₃–PbTiO₃ solid solution with distinctive magnetic signature.

Short range magnetic exchange interaction favors ferroelectricity

Multiferroics, where two or more ferroic order parameters coexist, is one of the hottest fields in condensed matter physics and materials science. To search multiferroics, currently most researches are focused on frustrated magnets, which usually have complicated magnetic structure and low magnetic ordering temperature. Here, we argue that actually simple interatomic magnetic exchange interaction already contains a driving force for ferroelectricity, thus providing a new microscopic mechanism for the coexistence and strong coupling between ferroelectricity and magnetism. We demonstrate this mechanism by showing that even the simplest antiferromagnetic insulator like MnO, could display a magnetically induced ferroelectricity under a biaxial strain. In addition, we show that such mechanism also exists in the most important single phase multiferroics, i.e. BiFeO3, suggesting that this mechanism is ubiquitous in systems with superexchange interaction.

Prospects for Ferroelectrics: 2012–2022

A review is given of more than a dozen subtopics within the general study of ferroelectrics, with emphasis upon controversies, unsolved problems, and prospects for the next decade, including pure science and industrial applications. The review emphasizes work over the past two years, from 2010 to 2012.

Magnetic control of ferroelectric interfaces

We report the strong magnetic field dependence of ferroelectric PbZr(0.52)Ti(0.48)O(3) (PZT) films on half-metallic oxide La(0.67)Sr(0.33)MnO(3) (LSMO) electrodes. As the field H is increased, the hysteresis loop first broadens (becomes lossy) and then disappears at approximately H = 0.34 T and ambient temperatures. The data are compared with the theories of Pirč et al (2009 Phys. Rev. B 79 214114), Parish and Littlewood (2008 Phys. Rev. Lett. 101 166602) and Catalan (2006 Appl. Phys. Lett. 88 102902). The results are interpreted as due not to magnetocapacitance but to the sharp negative magnetoresistance in LSMO at low magnetic fields (Hwang et al 1996 Phys. Rev. Lett. 77 2041), which causes a dramatic increase in leakage current through the PZT.

Recent progress in multiferroic magnetoelectric composites: from bulk to thin films

Multiferroic magnetoelectric composite systems such as ferromagnetic-ferroelectric heterostructures have recently attracted an ever-increasing interest and provoked a great number of research activities, driven by profound physics from coupling between ferroelectric and magnetic orders, as well as potential applications in novel multifunctional devices, such as sensors, transducers, memories, and spintronics. In this Review, we try to summarize what remarkable progress in multiferroic magnetoelectric composite systems has been achieved in most recent few years, with emphasis on thin films; and to describe unsolved issues and new device applications which can be controlled both electrically and magnetically.

Multiferroic thin-film integration onto semiconductor devices

This review deals with thin films of single-phase materials which exhibit two primary ferroic properties, namely ferroelectricity and (anti)ferromagnetism, deposited directly or through buffer layers onto semiconductors. It is the electrical control of ferromagnetism and magnetic control of ferroelectricity at room temperature and resulting device functionality that served as the driving force for the recent widespread research activities in this field. Although Gilbert demonstrated in 1600 that electrostatics (amber) do not couple to magnetostatics (compass needles), charges in motion certainly couple to magnetism, as shown later by Oersted and epitomized by Maxwell's theoretical derivation of the properties of electromagnetic waves. We survey the important contributions of various eminent physicists, from Curie to Dzyaloshinskii and Astrov to Schmid, without whom this field of research might not have developed. Most of the known multiferroic materials are classified into different groups, primarily based on Khomskii's classification of oxide multiferroics. We follow this with a brief discussion on the device application of multiferroics with semiconductor integration.

Novel room temperature multiferroics for random access memory elements

We have fabricated a variety of PZT-PFW (P bZr₀.₅₂Ti₀.₄₈O₃)1-x(PbFe₂/₃W₁/₃O₃)x [PZTFWx; 0.2 < x <0.4] single-phase tetragonal ferroelectrics via chemical solution deposition [polycrystalline] and pulsed laser deposition [epitaxial] onto Pt/Ti/SiO2/Si(100) and SrTiO₃/Si substrates. These exhibit ferroelectricity and (weak) ferromagnetism above room temperature with strain coupling via electrostriction and magnetostriction. Application of modest magnetic field strength (μ₀H < 1.0 T) destabilizes the long-range ferroelectric ordering and switches the polarization from approximately 22 μC/cm² (0.22 C/m²) to zero (relaxor state). This offers the possibility of three-state logic (+P, 0, -P) and magnetically switched polarizations. Because the switching is of large magnitude (unlike the very small nanocoulomb per centimeter squared values in terbium manganites) and at room-temperature, commercial devices should be possible.