Multiferroic magnetoelectric composite nanostructures

Abstract

R esearch on the magnetoelectric (ME) eff ect, discovered more than a century ago [1], progressed through pioneering work in the 1950s and 1960s, and has now seen a resurgence driven by long-term technological aspirations. With the trends toward device miniaturization, there is ever-increasing interest in combining electronic and magnetic properties into multifunctional materials to produce a single device component that can perform more than one task. Multiferroic ME materials are particularly appealing not only because they have the properties of their parent compounds, but also because interactions between the magnetic and electric orders lead to additional functionalities.From the viewpoint of material constituents, multiferroic ME materials can essentially be divided into two types: single-phase [2,3] and composite [4,5]. According to the original defi nition, a singlephase multiferroic material is one that possesses at least two of the 'ferroic' properties, such as ferroelectricity, ferromagnetism or ferroelasticity. While ME composites are multiphase materials composed of diff erent phases, neither phase supports the ME eff ect.Magnetoelectric coupling describes the infl uence of a magnetic (electric) fi eld on the polarization (magnetization) of a material. It may arise directly between the two order parameters as in single-phase multiferroics, or indirectly via strain/stress as in ME composites. Several recent articles have summarized and reviewed research progress in single-phase multiferroic ME materials [2,3], and accordingly, this review will instead focus on composite multiferroic materials.Th e ME eff ect in composite materials is known as a product tensor property, fi rst proposed by van Suchtelen in 1972 [5], that results from the cross interaction between the two phases in the composite. As illustrated schematically in Figure 1, the composite ME eff ect is a result of the product of the magnetostrictive eff ect (magnetic/mechanical eff ect) in the magnetic phase and the piezoelectric eff ect (mechanical/ electrical eff ect) in the piezoelectric phase. Multiferroic magnetoelectric composite nanostructuresYao Wang, Jiamian Hu, Yuanhua Lin and Ce-Wen Nan * Tsinghua University, ChinaMultiferroics are attracting increasing interest and provoking much research activity driven by the profound physics of these materials, the coexistence and coupling of ferroelectric and magnetic orders, and the potential applications in novel multifunctional devices such as sensors, transducers, memories and spintronics. Multiferroic magnetoelectric (ME) composite systems, such as ferromagnetic-ferroelectric heterostructures, which off er a novel route for integrating ferroelectric and ferromagnetism, have been widely studied in recent years. In these ME composite systems, ME coupling is strain-mediated, that is, the strain induced in one component, either by magnetostriction in the ferromagnetic or by the piezoelectric eff ect in the ferroelectric, is transferred to the other component, altering the polarization or ma...

Film size-dependent voltage-modulated magnetism in multiferroic heterostructures

“…the converse magnetoelectric (ME) effect, has become a central issue in the fields of spintronics and multiferroics [1][2][3][4][5][6][7][8][9][10]. It can provide a fast and extremely energy-efficient way for modulating magnetism compared with the traditional way of using external magnetic fields or spin currents [11], and has thus tremendous potential in future low-power and [ [51][52][53][54][55] (for details, see comprehensive review [10]).…”

“…It can provide a fast and extremely energy-efficient way for modulating magnetism compared with the traditional way of using external magnetic fields or spin currents [11], and has thus tremendous potential in future low-power and [ [51][52][53][54][55] (for details, see comprehensive review [10]). Compared with the strains which can normally be sustained throughout the heterostructure [5][6][7][8], such charge-driven ME effects can only occur at the heterointerface ranging from the first few atomic layers to several nanometres (normally less than 10 nm) depending on the charge screening length of a specific magnetic film [9,10]. As a result, such charge effects may become remarkable only when the thickness of the magnetic film and/or the heterostructure becomes small.…”

Interface induced out-of-plane magnetic anisotropy in magnetoelectric BiFeO3-BaTiO3 superlattices

“…This strain is mechanically transferred to the magnetic component, inducing a magnetization change through the piezomagnetic effect. 10,11 Thin multilayered films with strong out-of-plane (OOP) magnetic anisotropy, i.e., magnetization aligned perpendicular to the film surface, are the best candidates for next-generation non-volatile memory. In such systems, there is a large energy barrier for magnetization switching, implying higher stability of the magnetization states, and lower critical current for spintransfer torque memory devices.…”

“…16 It is well known that bulk BiFeO 3 is a G-type antiferromagnet possessing a cycloidal spin structure with a period of 62 nm. 17 The magnetic moment gradually rotates in the plane determined by the propagation direction of the cycloid [1][2][3][4][5][6][7][8][9][10] and the polarization direction [111], which is the principal axis of the electric field gradient (EFG) tensor (Fig. 1).…”

Electric in-plane polarization in multiferroic CoFe2O4/BaTiO3 nanocomposite tuned by magnetic fields

“…Because the choice of single-phase multiferroic materials being suitable at room temperature is limited, the use of magnetoelectric two-phase composites has proven to be more promising 2 . Recently, even classic materials such as ferromagnetic Fe and ferroelectric BaTiO 3 (BTO) have been shown as potentially useful 3 .…”