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

Electrons have a charge and a spin, but until recently these were considered separately. In classical electronics, charges are moved by electric fields to transmit information and are stored in a capacitor to save it. In magnetic recording, magnetic fields have been used to read or write the information stored on the magnetization, which 'measures' the local orientation of spins in ferromagnets. The picture started to change in 1988, when the discovery of giant magnetoresistance opened the way to efficient control of charge transport through magnetization. The recent expansion of hard-disk recording owes much to this development. We are starting to see a new paradigm where magnetization dynamics and charge currents act on each other in nanostructured artificial materials. Ultimately, 'spin currents' could even replace charge currents for the transfer and treatment of information, allowing faster, low-energy operations: spin electronics is on its way.

/pdf/the-emergence-of-spin-electronics-in-data-storage-1vrnm5549k.pdf

The emergence of spin electronics in data storage

http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

Multiferroic magnetoelectric composite systems such as ferromagnetic-ferroelectric heterostructures have recently attracted an ever-increasing interest and provoked a great number of research activities, driven by profound physics from coupling between ferroelectric and magnetic orders, as well as potential applications in novel multifunctional devices, such as sensors, transducers, memories, and spintronics. In this Review, we try to summarize what remarkable progress in multiferroic magnetoelectric composite systems has been achieved in most recent few years, with emphasis on thin films; and to describe unsolved issues and new device applications which can be controlled both electrically and magnetically.

Recent Progress in Multiferroic Magnetoelectric Composites: from Bulk to Thin Films

We show that the in-plane magnetoresistance of sandwiches of uncoupled ferromagnetic (${\mathrm{Ni}}_{81}$${\mathrm{Fe}}_{19}$,${\mathrm{Ni}}_{80}$${\mathrm{Co}}_{20}$,Ni) layers separated by ultrathin nonmagnetic metallic (Cu,Ag,Au) layers is strongly increased when the magnetizations of the two ferromagnetic layers are aligned antiparallel. Using NiFe layers, we report a relative change of resistance of 5.0% in 10 Oe at room temperature. The comparison between different ferromagnetic materials (alloys or pure elements) leads us to emphasize the role of bulk rather than interfacial spin-dependent scattering in these structures, in contrast to Fe/Cr multilayers.

Giant magnetoresistive in soft ferromagnetic multilayers.

Two types of patterned, unshielded Giant MagnetoResistance (GMR) spin valve sensors have been fabricated: nano-layered NiFe/Co/Cu/Co/NiFe and simpler NiFe/Cu/Co spin valves. GMR values of 7.6% for /spl Delta/H=10 Oe were measured for the nano-layered structures on coupons. Transfer curves in uniform fields were obtained and were in agreement with theoretical expectations. The sensors were highly linear and well biased. Optimum biasing of the free layer in the spin valve sensor has new features over that in AMR sensors. These were explored in shielded as well as unshielded spin valves using micromagnetic simulation. >

Design and operation of spin valve sensors

Spin-valve effect in soft ferromagnetic sandwiches

We present comprehensive results on the magnetoresistive properties of spin-valve sandwiches comprising glass/M(1)/Cu/${\mathrm{Ni}}_{80}$${\mathrm{Fe}}_{20}$/${\mathrm{Fe}}_{50}$${\mathrm{Mn}}_{50}$/Cu, where M(1) is a ferromagnetic transition metal or alloy (Co,Ni,${\mathrm{Ni}}_{80}$${\mathrm{Fe}}_{20}$). We discuss the thermal variation of the magnetoresistance (\ensuremath{\Delta}R/R) and its dependence on the thicknesses of the layers constituting the active part of the spin-value sandwich [i.e., M(1)/Cu/NiFe]. An almost linear decrease of \ensuremath{\Delta}R/R is observed between 77 and 320 K. For a given ferromagnetic material, \ensuremath{\Delta}R/R extrapolates to zero at a temperature ${\mathit{T}}_{0\mathrm{S}\mathrm{V}}$ significantly lower than the Curie temperature, and independent of the ferromagnetic layer thickness. We have identified spin-\ensuremath{\uparrow} and spin-\ensuremath{\downarrow} intermixing by spin-wave scattering as responsible for the thermal decrease of the magnetoresistance. We show that the magnetoresistance arises within the ``active'' parts of the ferromagnetic layers of thickness of about 90 \AA{} located next to the M/Cu interfaces. We give a phenomenological expression relating \ensuremath{\Delta}R/R to the longer of the two spin-dependent mean free paths, and to current shunting in the inactive part of the sandwich. The thickness of the active region is independent of temperature.

Giant magnetoresistance of magnetically soft sandwiches: Dependence on temperature and on layer thicknesses.

We show that the giant magnetoresistance in sputtered Ni-Fe/Cu/Ni-Fe/Fe-Mn spin-valve structures is strongly reduced by the presence of compositionally intermixed regions at the NiFe/Cu interfaces. The ultrathin intermixed layers, which are not ferromagnetic, are centers of strong spin-independent scattering, thus reducing the flow of polarized electrons from one ferromagnetic layer to the other. Our results show that interfacial spin-independent scattering must be included in the theory of giant magnetoresistance

B.A. Gurney

Papers

Giant magnetoresistive in soft ferromagnetic multilayers.

Design and operation of spin valve sensors

Spin-valve effect in soft ferromagnetic sandwiches

Giant magnetoresistance of magnetically soft sandwiches: Dependence on temperature and on layer thicknesses.

Role of interfacial mixing in giant magnetoresistance.