Electric-Field Control of Exchange Bias in Multiferroic Epitaxial Heterostructures

Abstract

The magnetic exchange between epitaxial thin films of the multiferroic (antiferromagnetic and ferroelectric) hexagonal YMnO 3 oxide and a soft ferromagnetic (FM) layer is used to couple the magnetic response of the FM layer to the magnetic state of the antiferromagnetic one. We will show that biasing the ferroelectric YMnO 3 layer by an electric field allows control of the magnetic exchange bias and subsequently the magnetotransport properties of the FM layer. This finding may contribute to paving the way towards a new generation of electric-field controlled spintronic devices. DOI: 10.1103/PhysRevLett.97.227201 PACS numbers: 75.70.Cn, 85.80.Jm Multiferroic materials have been proposed for building a new generation of devices in spintronics, eventually allowing us to overcoming critical limitations in technology [1]. Much effort has been directed to searching for materials displaying the elusive coexistence of ferroelectricity (FE) and ferromagnetism (FM) [2,3], which is thought to be essential for progress in this direction. In contrast, materials displaying coupled FE and antiferromagnetic (AF) behavior have received much less attention. To exploit the multiferroic character of a material, it is essential that the ferroic properties (magnetic and electric, in the present context) are coupled. Hexagonal YMnO 3 (YMO), in bulk form, is ferroelectric up to 900 K and exhibits an antiferromagnetic character at low temperature (T N 90 K). It has been shown that in YMO single crystals, both order parameters are coupled [4], and this observation has triggered a renewed attention to this oxide [5,6]. The electric polarization axis of YMO is along the c axis; the Mn atomic spins lie in a perpendicular plane, forming a two dimensional, frustrated antiferromagnetic, triangular network [7,8]. Hence, in principle, one could use AF YMO to pin the magnetic state of a FM material and subsequently exploit its ferroelectric character and the coupling between FE and AF order parameters to tailor the properties of the FM layer. As a first step, it has been recently shown that indeed it is possible to exchange-bias NiFe (Permalloy-Py) with AF epitaxial (0001) YMO films which display a remanent electric polarization [5].Attempts towards electric-field control of exchange bias have been recently reported by Borisov et al. using magnetoelectric, but not multiferroic (AF) Cr 2 O 3 single crystals as pinning layers [9]. Here, we will show that it is possible to grow heterostructures that, exploiting the AF and FE character of YMO, allow us to control the magnetic state of a FM layer by an electric field. For that purpose, an epitaxial layer of YMO has been sandwiched between metallic electrodes (Pt and Py), and the exchange bias between YMO and Py has been monitored as a function of a biasing electric field applied across the YMO layer [ Fig. 1(b)].When a magnetic field is applied parallel to the interface between FM and AF materials, the magnetization of the FM layer does not follow (neglecting the anisotropy of the FM layer) the ex...

Magnetoelectric coupling across the interface of multiferroic nanocomposites

“…With the increase of the electric field, the magnetic anisotropy became stronger. Similar effect can be observed in Py/YMO herterostructure as well [31]. In 2013, Buzzi et al [32] observed a 90° rotation of magnetization due to the switching of out-of-plane ferroelectric polarization in artificial multiferroic nanostructures (arrays of Ni on PMN-PT substrates).…”

Probing electric field control of magnetism using ferromagnetic resonance

“…1a 17 . We image the magnetic structure of the CoFe layer at zero magnetic field using scanning electron microscopy with polarization analysis (SEMPA) 38 . By measuring the spin polarization of secondary electrons, SEMPA directly measures the local vector magnetization in the CoFe layer 39 .…”

Multi-ferroic and magnetoelectric materials and interfaces

“…The most promising single-phase MF materials to use as an AFM pinning layer are YMnO 3 and BiFeO 3 . ME control of the exchange bias has been demonstrated at YMnO 3 /NiFe interfaces [140]. However, this effect is irreversible and exists only at low temperatures.…”