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.

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Spintronics: Fundamentals and applications

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

Multiferroic magnetoelectrics are materials that are both ferromagnetic and ferroelectric in the same phase. As a result, they have a spontaneous magnetization that can be switched by an applied magnetic field, a spontaneous polarization that can be switched by an applied electric field, and often some coupling between the two. Very few exist in nature or have been synthesized in the laboratory. In this paper, we explore the fundamental physics behind the scarcity of ferromagnetic ferroelectric coexistence. In addition, we examine the properties of some known magnetically ordered ferroelectric materials. We find that, in general, the transition metal d electrons, which are essential for magnetism, reduce the tendency for off-center ferroelectric distortion. Consequently, an additional electronic or structural driving force must be present for ferromagnetism and ferroelectricity to occur simultaneously.

Why Are There so Few Magnetic Ferroelectrics

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

We have studied the magnetoresistance of (001)Fe/(001)Cr superlattices prepared by molecularbeam epitaxy. A huge magnetoresistance is found in superlattices with thin Cr layers: For example, with ${t}_{\mathrm{Cr}}=9$ \AA{}, at $T=4.2$ K, the resistivity is lowered by almost a factor of 2 in a magnetic field of 2 T. We ascribe this giant magnetoresistance to spin-dependent transmission of the conduction electrons between Fe layers through Cr layers.

/pdf/giant-magnetoresistance-of-001-fe-001-cr-magnetic-4n464berkj.pdf

Giant magnetoresistance of (001)Fe/(001)Cr magnetic superlattices.

We describe the magnetic and transport properties of Fe(001)/Cr(001) superlattices grown on GaAs (001) by molecular‐beam epitaxy and characterized by reflection high‐energy electron diffraction (RHEED), Auger spectroscopy, x‐ray diffraction, and electron microscopy. For Cr layers thinner than about 30 A the magnetic behavior reveals strong antiferromagnetic couplings between the Fe layers across the Cr layers. Polarized neutron diffraction experiments confirm the existence of an antiferromagnetic superstructure. We discuss the origin of the antiferromagnetic (AF) coupling. The Fe/Cr superlattices with AF interlayer coupling exhibit a giant magnetoresistance: when an applied field aligns the magnetizations of the Fe layers, the resistivity drops by a factor of 2 for some samples. This giant magnetoresistance can be ascribed to the spin dependence of the electron scattering by interfaces. We compare our results with the predictions of two recent theoretical models.

/pdf/magnetic-and-transport-properties-of-fe-cr-superlattices-14wnq4yep6.pdf

Magnetic and transport properties of Fe/Cr superlattices (invited)

Magnetoresistance of Fe/Cr superlattices

An extensive experimental study by magnetic-resistivity, magnetostriction, and thermal-expansion measurements on a single crystal of the hexagonal ${\mathrm{PrNi}}_{5}$ compound is presented. The magnetoelastic results are quite satisfactorily interpreted within a model involving the crystal-field and quadrupolar interactions acting on the Pr ions and taking into account the Ni contribution. All the unusual features, especially the maxima observed around 15 K in the thermal variations of these properties, arise from crystal-field effects which lead to a nonmagnetic singlet ground state lying about 40 K below the first magnetic level. The induced Ni magnetism, although very small, strongly influences the observed behavior, especially the high-temperature magnetic susceptibility. The magnetoelastic coefficients ${B}^{\ensuremath{\alpha}1}$ and ${B}^{\ensuremath{\alpha}2}$ and the total quadrupolar coefficients ${G}^{\ensuremath{\alpha}}$ and ${G}^{\ensuremath{\epsilon}}$ were determined, leading to the experimental evidence of antiferroquadrupolar interactions between rare-earth ions in ${\mathrm{PrNi}}_{5}$.

G. Creuzet

Papers

Giant magnetoresistance of (001)Fe/(001)Cr magnetic superlattices.

Magnetic and transport properties of Fe/Cr superlattices (invited)

Magnetoresistance of Fe/Cr superlattices

Magnetic and magnetoelastic properties of PrNi 5 single crystal

SPECIFIC HEAT AND PRESSURE EFFECTS IN THE KONDO LATTICE COMPOUND CePt2Si2