There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

This review describes a new paradigm of electronics based on the spin degree of freedom of the electron. Either adding the spin degree of freedom to conventional charge-based electronic devices or using the spin alone has the potential advantages of nonvolatility, increased data processing speed, decreased electric power consumption, and increased integration densities compared with conventional semiconductor devices. To successfully incorporate spins into existing semiconductor technology, one has to resolve technical issues such as efficient injection, transport, control and manipulation, and detection of spin polarization as well as spin-polarized currents. Recent advances in new materials engineering hold the promise of realizing spintronic devices in the near future. We review the current state of the spin-based devices, efforts in new materials fabrication, issues in spin transport, and optical spin manipulation.

http://science.sciencemag.org/content/sci/294/5546/1488.full.pdf

Spintronics: a spin-based electronics vision for the future.

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

/pdf/spintronics-fundamentals-and-applications-2dx38n6phu.pdf

Spintronics: Fundamentals and applications

A ferroelectric crystal exhibits a stable and switchable electrical polarization that is manifested in the form of cooperative atomic displacements. A ferromagnetic crystal exhibits a stable and switchable magnetization that arises through the quantum mechanical phenomenon of exchange. There are very few 'multiferroic' materials that exhibit both of these properties, but the 'magnetoelectric' coupling of magnetic and electrical properties is a more general and widespread phenomenon. Although work in this area can be traced back to pioneering research in the 1950s and 1960s, there has been a recent resurgence of interest driven by long-term technological aspirations.

/pdf/multiferroic-and-magnetoelectric-materials-2fpof7uzog.pdf

Multiferroic and magnetoelectric materials

A negative isotropic magnetoresistance effect more than three orders of magnitude larger than the typical giant magnetoresistance of some superlattice films has been observed in thin oxide films of perovskite-like La0.67Ca0.33MnOx. Epitaxial films that are grown on LaAIO3 substrates by laser ablation and suitably heat treated exhibit magnetoresistance values as high as 127,000 percent near 77 kelvin and ∼1300 percent near room temperature. Such a phenomenon could be useful for various magnetic and electric device applications if the observed effects of material processing are optimized. Possible mechanisms for the observed effect are discussed.

http://science.sciencemag.org/content/sci/264/5157/413.full.pdf

Thousandfold Change in Resistivity in Magnetoresistive La-Ca-Mn-O Films

The conduction-f electron interaction (k-f interaction) can be probed by the investigation of the transport properties. We will focus on the specific effects -anisotropic magnetoresistance and extraordinary Hall effect- which are related to the anisotropy of the k-f interaction. We describe studies on metals containing rare earth (RE) impurities, RE metals and intermetallic compounds and amorphous alloys successively and we discuss the data obtained on the anisotropy of the k-f interaction.

Magneto-Transport in f-Electron Systems — Quadrupole and Orbital Exchange Effects

Dispositif a memoire (10), comprenant au moins un element spintronique (11) adapte pour representer un etat parmi au moins n etats associes a l'element spintronique, n>1, caracterise en ce que chacun des n etats est associe a au moins une caracteristique d'un ensemble de skyrmions magnetiques (1) dans l'element spintronique, et en ce que ladite caracteristique associee a un etat n°i est distincte de ladite caracteristique associee a un etat n°j lorsque les etat n°i et j sont deux etats distincts parmi les n etats.

Dispositif a memoire, comprenant au moins un element spintronique et procede associe

An interesting point of investigation in high T c superconductors concerns the problems of pinning of the vortices. It is known that their motion can be monitored on the one hand by the ratio between their pinning energy and the thermal activation energy, and on the other hand by the driving forces generated by an applied magnetic field. For a temperature near T c , a flux flow behaviour is expected, characterized by a frequency dependence of the motion of flux lines. Hysteresis cycles in a.c. magnetic field were measured for a YBa2Cu3O7−x single crystal with the applied field perpendicular to the c axis. The hysteresis losses were studied as a function of field amplitude (0–250 Oe), frequency (0.5–100 Hz) and temperature (4.2–90 K). It is pricipally shown that near T c the hysteresis loops are frequency dependent, and that the associated losses present, for aiven amplitude, a maximum for a temperature T ∗ corresponding to full field penetration in the sample. The behaviour of the hysteresis losses as a function of frequency is analysed on the basis of a flux flow model.

Study of vortex dynamics in YBa2Cu3O7−x by hysteresis cycle measurements

L'invention concerne un systeme (10) de generation de skyrmions comprenant : - un canon (12) comportant une region formant paroi (14) realisee en un premier materiau, la region (14) delimitant un espace exterieur (16) realise dans un deuxieme materiau distinct du premier materiau et un espace interieur (18) realise dans un troisieme materiau distinct du premier materiau, le deuxieme materiau et le troisieme materiau etant des materiaux magnetiques, et - un dispositif de renversement (26) de l'aimantation magnetique propre a renverser l'aimantation magnetique a l'interface entre la region (14) et l'espace interieur (18).

Systeme de generation de skyrmions

The spin Hall effect (SHE) [1] allows for a reciprocal conversion between charge and spin currents using the spin orbit coupling which can be at the core of several promising spintronics devices. The spin orbit interaction is used to produce a transverse flow of spin or charge in response to a longitudinal excitation, these are the direct or inverse SHE. The spin Hall angle (SHA), the ratio of longitudinal and transverse electronic conductivities, is the characterizing parameter of this conversion. So far, large SHA have been reported in transition metals like Pt, Pd, W, Beta-Ta and in a few alloys with large spin orbit coupling impurities: CuIr, CuBi or CuPb [2]. In this presentation we will report on our study of the SHA in AuW alloys [3] which exhibits a non-monotonic relation with the W concentration. In the regime of diluted alloys the behaviour suggests a dominant side-jump contribution to the spin Hall resistivity, the SHA increasing with the W concentration. We will present experiments demonstrating the requirement of new spin-absorption model in lateral spin valves adapted to the case of strong spin absorption for a correct evaluation of the SHA. Altogether with complementary Ferromagnetic Resonance Spin-Pumping studies, it then leads to SHA as large as +15%. At higher W content the SHA sign is reversed, becoming negative as for pure W.

/pdf/spin-hall-effect-in-5d-au-w-transition-metal-alloys-32siwpghvt.pdf

Albert Fert

Papers

Magneto-Transport in f-Electron Systems — Quadrupole and Orbital Exchange Effects

Dispositif a memoire, comprenant au moins un element spintronique et procede associe

Study of vortex dynamics in YBa2Cu3O7−x by hysteresis cycle measurements

Systeme de generation de skyrmions

Spin Hall effect in 5d Au: W transition metal alloys(Conference Presentation)