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

Presents a study by susceptibility measurements of the Neel temperature concentration dependence in both antiferromagnetic series: Fe1-xCdxCl2 and Fe1-xMnxCl2. At low cadmium or manganese concentrations, the order temperature decreases linearly with x, TN(x)= TN(0)(1- alpha x) where alpha =1.79 for the manganese series and alpha =2.18 for the cadmium series. In Fe1-xCdxCl2, the order temperature falls to zero near x=0.45. This concentration is close to the two-dimensional triangular lattice percolation threshold. In Fe1-xMnxCl2, the Fe-Mn and Mn-Mn exchange interactions maintain the long-range order over the whole concentration range, the concentration dependence of TN incurves and slowly decreases to the Neel temperature of pure MnCl2 (TN approximately 2K). The authors discuss these behaviours by comparison with some recent theoretical studies.

Neel temperatures of dilute Fe 1-x Cd x Cl 2 and mixed Fe 1-x Mn x Cl 2 by susceptibility measurements

In order to interpret the magnetic anisotropy of spin‐glass alloys, we calculate the anisotropic terms arising in the RKKY interaction between transition metal impurities when spin‐orbit coupling is taken into account. We find pseudo‐dipole and single ion anisotropy terms in the pair interaction and Dzyaloshinsky‐Moriya terms when triangles of impurities are considered. Applying our results to AuFe alloys we find that, although the pseudo‐dipole interactions are 40 times stronger than the magnetic dipole‐dipole, the Dzyaloshinsky‐Moriya interactions are even stronger and are sufficient to explain the magnetic anisotropy observed in AuFe spin‐glass alloys.

Origin of magnetic anistropy in transition metal spin‐glass alloys

We present magnetization and resistivity measurements on single crystals of yttrium doped with small concentrations of gadolinium (c=1, 2, and 3 at. %). The low‐field susceptibility exhibits a spin‐glass‐like sharp cusp for the magnetic field along the c axis. However, there is no irreversible behavior below the temperature of the cusp, which rules out the existence of a spin‐glass state. Moreover, our magnetization measurements show up a spin‐flop transition for H in the basal plane. The existence of a long‐range ordering is confirmed by our resistivity measurements. The resistivity parallel to the c axis exhibits a maximum just below the ordering temperature, which is reminiscent of the superzone effects observed in many rare‐earth metals. The antiferro‐ magneticlike properties of the YGd alloys contrast with the spin‐glass behavior observed in other Y–rare‐earth alloys at similar concentrations.

Magnetic ordering in YGd alloys

Amorphous alloys containing small concentrations of rare earths exhibit very different magnetic properties for Pr (strong singlet ground state effects), Tm (smaller singlet effects), and Dy or Er (small deviations from the free ion behavior). All the experimental results for different rare earths in a given host can be accounted for by a unique distribution of nonuniaxial quadratic crystal fields. The distribution of local symmetries is not consistent with random dense packing of hard spheres and suggests well defined local angular correlations.

Albert Fert

Papers

Neel temperatures of dilute Fe 1-x Cd x Cl 2 and mixed Fe 1-x Mn x Cl 2 by susceptibility measurements

Origin of magnetic anistropy in transition metal spin‐glass alloys

Magnetic ordering in YGd alloys

Crystal electric field and local symmetry in rare‐earth amorphous alloys

Growth of single-crystal Fe/Cr magnetic multilayer structures on (001) GaAs by molecular beam epitaxy