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

In this review paper, we summarize the performance (in particular the magnetic field resolution), micro-fabrication technologies and applications of micrometer sized Hall effect devices. Additionally, our activities in this domain are briefly described.

Micro-Hall devices: performance, technologies and applications

Recent discoveries of large magnetoresistance in non-magnetic semiconductors have gained much attention because the size of the effect is comparable to, or even larger than, that of magnetoresistance in magnetic systems. Conventional magnetoresistance in doped semiconductors is straightforwardly explained as the effect of the Lorentz force on the carrier motion, but the reported unusually large effects imply that the underlying mechanisms have not yet been fully explored. Here we report that a simple device, based on a lightly doped silicon substrate between two metallic contacts, shows a large positive magnetoresistance of more than 1,000 per cent at room temperature (300 K) and 10,000 per cent at 25 K, for magnetic fields between 0 and 3 T. A high electric field is applied to the device, so that conduction is space-charge limited. For substrates with a charge carrier density below approximately 10(13) cm(-3), the magnetoresistance exhibits a linear dependence on the magnetic field between 3 and 9 T. We propose that the observed large magnetoresistance can be explained by quasi-neutrality breaking of the space-charge effect, where insufficient charge is present to compensate the electrons injected into the device. This introduces an electric field inhomogeneity, analogous to the situation in other semiconductors in which a large, non-saturating magnetoresistance was observed. In this regime, the motions of electrons become correlated, and thus become dependent on magnetic field. Although large positive magnetoresistance at room temperature has been achieved in metal-semiconductor hybrid devices, we have now realized it in a simpler structure and in a way different from other known magnetoresistive effects. It could be used to develop new magnetic devices from silicon, which may further advance silicon technology.

Large positive magnetoresistive effect in silicon induced by the space-charge effect

Magnetic recording read head sensor technology

The magnetoresistance at temperatures below 20 K in an $n\text{-InSb}/{\text{In}}_{0.85}{\text{Al}}_{0.15}\text{Sb}$ two-dimensional electron system is studied and described in terms of antilocalization due to quantum interference under strong spin-orbit interaction. The spin-orbit interaction coefficients are extracted by fitting the magnetoresistance data to an antilocalization theory distinguishing the Rashba and Dresselhaus contributions. A good agreement between magnetoresistance data and theory suggests a Rashba coefficient $|\ensuremath{\alpha}|\ensuremath{\approx}0.03\text{ }\text{eV}\text{ }\text{\AA{}}$ and a Dresselhaus coefficient $\ensuremath{\gamma}\ensuremath{\approx}490\text{ }\text{eV}\text{ }{\text{\AA{}}}^{3}$. A strong contribution from the Dresselhaus term leads to pronounced anisotropy in the energy splitting induced by spin-orbit interaction in the two-dimensional electron dispersion.

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Spin-orbit interaction determined by antilocalization in an InSb quantum well

A mesoscopic nonmagnetic magnetoresistive read-head sensor based on the recently reported extraordinary magnetoresistance (EMR) effect has been fabricated from a narrow-gap Si-doped InSb quantum well. The sensor has a conservatively estimated areal-density of 116 Gb/in.2 with a 300 K EMR of 6% and a current sensitivity of 147 Ω/T at a relevant field of 0.05 T and a bias of 0.27 T. Because this sensor is not subject to magnetic noise, which limits conventional sensors to areal densities of order 100 Gb/in.2, it opens a pathway to ultra-high-density recording at areal densities of order 1 Tb/in.2.

Nonmagnetic semiconductors as read-head sensors for ultra-high-density magnetic recording

The room temperature extraordinary magnetoresistance (EMR) of a mesoscopic sensor structure prepared from an InSb quantum well of dimension 30 nm wide/spl times/100 nm high/spl times/3 /spl mu/m long is reported. The observed EMR is 4.75% at a relevant field of 0.05 T. The advantages and disadvantages of this nonmagnetic composite semiconductor/metal structure relative to that of conventional magnetic giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) devices for use as read-heads in high-density magnetic recording are discussed.

Room temperature extraordinary magnetoresistance of nonmagnetic narrow-gap semiconductor/metal composites: application to read-head sensors for ultrahigh-density magnetic recording

M. B. Santos

Papers

Nonmagnetic semiconductors as read-head sensors for ultra-high-density magnetic recording

Room temperature extraordinary magnetoresistance of nonmagnetic narrow-gap semiconductor/metal composites: application to read-head sensors for ultrahigh-density magnetic recording