Tunnel magnetoresistance and robust room temperature exchange bias with multiferroic BiFeO3 epitaxial thin films

Abstract

We report on the functionalization of multiferroic BiFeO 3 epitaxial films for spintronics. A first example is provided by the use of ultrathin layers of BiFeO 3 as tunnel barriers in magnetic tunnel junctions with La 2/3 Sr 1/3 MnO 3 and Co electrodes. In such structures, a positive tunnel magnetoresistance up to 30% is obtained at low temperature. A second example is the exploitation of the antiferromagnetic spin structure of a BiFeO 3 film to induce a sizeable (~60 Oe) exchange bias on a ferromagnetic film of CoFeB, at room temperature.Remarkably, the exchange bias effect is robust upon magnetic field cycling, with no indications of training.1 Multiferroic materials [1,2], that display several long-range orders among ferroelectricity (FE), ferromagnetism (FM) and ferroelasticity, can bring interesting additional functionalities to spintronics [3]. For instance, the magnetoelectric coupling existing in these compounds could be used to rotate the magnetization of a ferromagnetic multiferroic element by applying an electric field, rather than a magnetic field. Unfortunately, very few multiferroics exhibit a finite magnetization (i.e. are ferromagnetic or ferrimagnetic). Most of them are antiferromagnetic (AF) or weak-ferromagnets. Still, many spintronics applications can also be devised exploiting the new functionalities provided by antiferromagnetic multiferroics (AFM). For example, Binek and Doudin [4] have proposed to use a thin AFM

Magnetoelectric coupling across the interface of multiferroic nanocomposites

“…The magnetization of CoFe layer could be reversibly switched by applying an electric field. Similar effect was also reported in BFO/Co 40 Fe 40 B 20 (CoFeB) structures [77].…”

Exchange bias effect and intragranular magnetoresistance in Nd0.84Sr0.16CoO3

“…FM, AFM, spin-glass (SG), cluster-glass (CG), ferrimagnetic (FI) systems [7,8,9,10]. The EB effect has also been evidenced through the systematic shifts in magnetoresistance-field (MR-H) curve which is limited to the bilayer or multilayer films only [11,12,13,14]. Recently, EB effect has been reported in few compounds attributed to the grain interior spontaneous phase separation where EB effect was reported through the shift in the magnetic hysteresis loop [9,10,15,16,17,18,19] In this article, we report a new paradigm of EB effect in a polycrystalline compound, Nd 0.84 Sr 0.16 CoO 3 through the shifts in the MR-H curve.…”

Polaronic Transport Induced by Competing Interfacial Magnetic Order in aLa0.7Ca0.3MnO3/BiFe

“…In these novel systems, different degrees of freedom (DOFs) (e.g., charge, spin, and orbital) are coupled at a single interface between two different oxide layers to form a new state that displays properties dramatically different from those of the individual layers [4][5][6][7][8]. Particular attention has been given to the coupling between ferromagnetic (FM), antiferromagnetic (AFM), and ferroelectric (FE) orders, as this could reveal new routes to realizing strong magnetoelectric coupling [1][2][3][9][10][11].Heterostructures consisting of manganite and multiferroic layers are particularly promising in this regard. The most extensively studied combination [2,3,9,10,12] consists of the colossal magnetoresistive manganite La 0.7 Sr 0.3 MnO 3 (LSMO) [or the similar compound La 0.7 Ca 0.3 MnO 3 (LCMO)], which is ferromagnetic below a critical temperature T c , and the canonical multiferroic BiFeO 3 (BFO), which has coexisting coupled AFM and FE phases in which the magnetization can be switched by an applied electric (E) field [13].…”

“…In these novel systems, different degrees of freedom (DOFs) (e.g., charge, spin, and orbital) are coupled at a single interface between two different oxide layers to form a new state that displays properties dramatically different from those of the individual layers [4][5][6][7][8]. Particular attention has been given to the coupling between ferromagnetic (FM), antiferromagnetic (AFM), and ferroelectric (FE) orders, as this could reveal new routes to realizing strong magnetoelectric coupling [1][2][3][9][10][11].…”

“…Particular attention has been given to the coupling between ferromagnetic (FM), antiferromagnetic (AFM), and ferroelectric (FE) orders, as this could reveal new routes to realizing strong magnetoelectric coupling [1][2][3][9][10][11].…”