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...

We report on experiments of spin filtering through ultrathin single-crystal layers of the insulating and ferromagnetic oxide BiMnO 3 ͑BMO͒. The spin polarization of the electrons tunneling from a gold electrode through BMO is analyzed with a counterelectrode of the half-metallic oxide La 2/3 Sr 1/3 MnO 3 ͑LSMO͒. At 3 K we find a 50% change of the tunnel resistances according to whether the magnetizations of BMO and LSMO are parallel or opposite. This effect corresponds to a spin-filtering efficiency of up to 22%. Our results thus show the potential of complex ferromagnetic insulating oxides for spin filtering and injection.

A large polarization in Ce-modified bismuth ferrite thin films effects on the ferroelectric and magnetic properties of chemical solution deposited Bi Fe O 3 thin films Several experimental methods to measure ferroelectric hysteresis loops and to extract polarization values are compared for thin films with significant losses and different magnitudes of polarization. The analysis allows the determination of the most appropriate frequency range and technique to extract reliable values of the remanent polarization in materials with low polarization and high leakage. Examples include multiferroic YMnO 3 and Bi 0.9 La 0.1 NiMnO 6 thin films.

We demonstrate that epitaxial strain engineering is an efficient method to manipulate the ferromagnetic and ferroelectric properties in BiFeO(3)-CoFe(2)O(4) columnar nanocomposites. On one hand, the magnetic anisotropy of CoFe(2)O(4) is totally tunable from parallel to perpendicular controlling the CoFe(2)O(4) strain with proper combinations of substrate and ferroelectric phase. On the other hand, the selection of the used substrate allows the growth of the rhombohedral bulk phase of BiFeO(3) or the metastable nearly tetragonal one, which implies a rotation of the ferroelectric polar axis from [111] to close to the [001] direction. Remarkably, epitaxy is preserved and interfaces are semicoherent even when lattice mismatch is above 10%. The broad range of sustainable mismatch suggests new opportunities to assemble epitaxial nanostructures combining highly dissimilar materials with distinct functionalities.

Epitaxial and fully strained SrRuO 3 thin films have been grown on SrTiO 3 (100). At initial stages the growth mode is three-dimensional-͑3D-͒like, leading to a finger-shaped structure aligned with the substrate steps and that eventually evolves into a 2D step-flow growth. We study the impact that the defect structure associated with this unique growth mode transition has on the electronic properties of the films. Detailed analysis of the transport properties of nanometric films reveals that microstructural disorder promotes a shortening of the carrier mean free path. Remarkably enough, at low temperatures, this results in a reinforcement of quantum corrections to the conductivity as predicted by recent models of disordered, strongly correlated electronic systems. This finding may provide a simple explanation for the commonly observed-in conducting oxidesresistivity minima at low temperature. Simultaneously, the ferromagnetic transition occurring at about 140 K, becomes broader as film thickness decreases down to nanometric range. The relevance of these results for the understanding of the electronic properties of disordered electronic systems and for the technological applications of SrRuO 3 -and other ferromagnetic and metallic oxides-is stressed.