Magnetoelectric Devices for Spintronics Fusil, S; Garcia, V; Barthélémy, A ...
Annual review of materials research,
07/2014, Letnik:
44, Številka:
1
Journal Article
Recenzirano
The control of magnetism by electric fields is an important goal for the future development of low-power spintronics. Various approaches have been proposed on the basis of either single-phase ...multiferroic materials or hybrid structures in which a ferromagnet is influenced by the electric field applied to an adjacent insulator (usually having a ferroelectric, piezoelectric, or multiferroic character). The electric field effect on magnetism can be driven by purely electronic or electrostatic effects or can occur through strain coupling. Here we review progress in the electrical control of magnetic properties (anisotropy, spin order, ordering temperature, domain structure) and its application to prototype spintronic devices (spin valves, magnetic tunnel junctions). We tentatively identify the main outstanding difficulties and give perspectives for spintronics and other fields.
The celebrated renaissance of the multiferroics family over the past ten years has also been that of its most paradigmatic member, bismuth ferrite (BiFeO3). Known since the 1960s to be a high ...temperature antiferromagnet and since the 1970s to be ferroelectric, BiFeO3 only had its bulk ferroic properties clarified in the mid-2000s. It is however the fabrication of BiFeO3 thin films and their integration into epitaxial oxide heterostructures that have fully revealed its extraordinarily broad palette of functionalities. Here we review the first decade of research on BiFeO3 films, restricting ourselves to epitaxial structures. We discuss how thickness and epitaxial strain influence not only the unit cell parameters, but also the crystal structure, illustrated for instance by the discovery of the so-called T-like phase of BiFeO3. We then present its ferroelectric and piezoelectric properties and their evolution near morphotropic phase boundaries. Magnetic properties and their modification by thickness and strain effects, as well as optical parameters, are covered. Finally, we highlight various types of devices based on BiFeO3 in electronics, spintronics, and optics, and provide perspectives for the development of further multifunctional devices for information technology and energy harvesting.
The spin-orbit interaction couples the electrons' motion to their spin. As a result, a charge current running through a material with strong spin-orbit coupling generates a transverse spin current ...(spin Hall effect, SHE) and vice versa (inverse spin Hall effect, ISHE). The emergence of SHE and ISHE as charge-to-spin interconversion mechanisms offers a variety of novel spintronic functionalities and devices, some of which do not require any ferromagnetic material. However, the interconversion efficiency of SHE and ISHE (spin Hall angle) is a bulk property that rarely exceeds ten percent, and does not take advantage of interfacial and low-dimensional effects otherwise ubiquitous in spintronic hetero- and mesostructures. Here, we make use of an interface-driven spin-orbit coupling mechanism-the Rashba effect-in the oxide two-dimensional electron system (2DES) LaAlO
/SrTiO
to achieve spin-to-charge conversion with unprecedented efficiency. Through spin pumping, we inject a spin current from a NiFe film into the oxide 2DES and detect the resulting charge current, which can be strongly modulated by a gate voltage. We discuss the amplitude of the effect and its gate dependence on the basis of the electronic structure of the 2DES and highlight the importance of a long scattering time to achieve efficient spin-to-charge interconversion.
A new spin for oxide interfaces Varignon, J.; Vila, L.; Barthélémy, A. ...
Nature physics,
04/2018, Letnik:
14, Številka:
4
Journal Article
Recenzirano
The variety of emergent phenomena occurring at oxide interfaces has made these systems the focus of intense study in recent years. We argue that spin–orbit effects in oxide interfaces provide a ...versatile handle to generate, control and convert spin currents, with a view towards low-power spintronics.
Phase separation is a cooperative process, the kinetics of which underpin the orderly morphogenesis of domain patterns on mesoscopic scales
. Systems of highly degenerate frozen states may exhibit ...the rare and counterintuitive inverse-symmetry-breaking phenomenon
. Proposed a century ago
, inverse transitions have been found experimentally in disparate materials, ranging from polymeric and colloidal compounds to high-transition-temperature superconductors, proteins, ultrathin magnetic films, liquid crystals and metallic alloys
, with the notable exception of ferroelectric oxides, despite extensive theoretical and experimental work on the latter. Here we show that following a subcritical quench, the non-equilibrium self-assembly of ferroelectric domains in ultrathin films of Pb(Zr
Ti
)O
results in a maze, or labyrinthine pattern, featuring meandering stripe domains. Furthermore, upon increasing the temperature, this highly degenerate labyrinthine phase undergoes an inverse transition whereby it transforms into the less-symmetric parallel-stripe domain structure, before the onset of paraelectricity at higher temperatures. We find that this phase sequence can be ascribed to an enhanced entropic contribution of domain walls, and that domain straightening and coarsening is predominantly driven by the relaxation and diffusion of topological defects. Computational modelling and experimental observation of the inverse dipolar transition in BiFeO
suggest the universality of the phenomenon in ferroelectric oxides. The multitude of self-patterned states and the various topological defects that they embody may be used beyond current domain and domain-wall-based
technologies by enabling fundamentally new design principles and topologically enhanced functionalities within ferroelectric films.
Controlling magnetism by means of electric fields is a key issue for the future development of low-power spintronics. Progress has been made in the electrical control of magnetic anisotropy, domain ...structure, spin polarization or critical temperatures. However, the ability to turn on and off robust ferromagnetism at room temperature and above has remained elusive. Here we use ferroelectricity in BaTiO3 crystals to tune the sharp metamagnetic transition temperature of epitaxially grown FeRh films and electrically drive a transition between antiferromagnetic and ferromagnetic order with only a few volts, just above room temperature. The detailed analysis of the data in the light of first-principles calculations indicate that the phenomenon is mediated by both strain and field effects from the BaTiO3. Our results correspond to a magnetoelectric coupling larger than previous reports by at least one order of magnitude and open new perspectives for the use of ferroelectrics in magnetic storage and spintronics.
Oxide Spintronics Bibes, M.; Barthelemy, A.
IEEE transactions on electron devices,
05/2007, Letnik:
54, Številka:
5
Journal Article
Recenzirano
Concomitant with the development of metal-based spintronics in the late 1980s and 1990s, important advances were made on the growth of high-quality oxide thin films and heterostructures. While this ...was at first motivated by the discovery of high-temperature superconductivity in perovskite Cu oxides, this technological breakthrough was soon applied to other transition-metal oxides and, notably, mixed-valence manganites. The discovery of colossal magnetoresistance in manganite films triggered intense research activity on these materials, but the first notable impact of magnetic oxides in the field of spintronics was the use of such manganites as electrodes in magnetic tunnel junctions, yielding tunnel magnetoresistance ratios that are one order of magnitude larger than what had been obtained with transition-metal electrodes. Since then, research on oxide spintronics has been intense, with the latest developments focused on diluted magnetic oxides and, more recently, on multiferroics. In this paper, the most important results on oxide spintronics was reviewed, emphasizing materials physics as well as spin-dependent transport phenomena, and finally give some perspectives on how the flurry of new magnetic oxides could be useful for next-generation spintronics devices
Abstract
After almost twenty years of intense work on the celebrated LaAlO
3
/SrTiO
3
system, the recent discovery of a superconducting two-dimensional electron gas (2-DEG) in (111)-oriented KTaO
3
...-based heterostructures injects new momentum to the field of oxides interface. However, while both interfaces share common properties, experiments also suggest important differences between the two systems. Here, we report gate tunable superconductivity in 2-DEGs generated at the surface of a (111)-oriented KTaO
3
crystal by the simple sputtering of a thin Al layer. We extract the superfluid stiffness of the 2-DEGs and show that its temperature dependence is consistent with a node-less superconducting order parameter having a gap value larger than expected within a simple BCS weak-coupling limit model. The superconducting transition follows the Berezinskii-Kosterlitz-Thouless scenario, which was not reported on SrTiO
3
-based interfaces. Our finding offers innovative perspectives for fundamental science but also for device applications in a variety of fields such as spin-orbitronics and topological electronics.
Abstract
Antiferromagnetic thin films are currently generating considerable excitement for low dissipation magnonics and spintronics. However, while tuneable antiferromagnetic textures form the ...backbone of functional devices, they are virtually unknown at the submicron scale. Here we image a wide variety of antiferromagnetic spin textures in multiferroic BiFeO
3
thin films that can be tuned by strain and manipulated by electric fields through room-temperature magnetoelectric coupling. Using piezoresponse force microscopy and scanning NV magnetometry in self-organized ferroelectric patterns of BiFeO
3
, we reveal how strain stabilizes different types of non-collinear antiferromagnetic states (bulk-like and exotic spin cycloids) as well as collinear antiferromagnetic textures. Beyond these local-scale observations, resonant elastic X-ray scattering confirms the existence of both types of spin cycloids. Finally, we show that electric-field control of the ferroelectric landscape induces transitions either between collinear and non-collinear states or between different cycloids, offering perspectives for the design of reconfigurable antiferromagnetic spin textures on demand.
The control of optical fields is usually achieved through the electro-optic or acousto-optic effect in single-crystal ferroelectric or polar compounds such as LiNbO3 or quartz. In recent years, ...tremendous progress has been made in ferroelectric oxide thin film technology-a field which is now a strong driving force in areas such as electronics, spintronics and photovoltaics. Here, we apply epitaxial strain engineering to tune the optical response of BiFeO3 thin films, and find a very large variation of the optical index with strain, corresponding to an effective elasto-optic coefficient larger than that of quartz. We observe a concomitant strain-driven variation in light absorption--reminiscent of piezochromism--which we show can be manipulated by an electric field. This constitutes an electrochromic effect that is reversible, remanent and not driven by defects. These findings broaden the potential of multiferroics towards photonics and thin film acousto-optic devices, and suggest exciting device opportunities arising from the coupling of ferroic, piezoelectric and optical responses.
PDF
