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

http://myweb.rz.uni-augsburg.de/~eckern/WEH-287/ABSTRACTS/ruitenbeek.pdf

Quantum properties of atomic-sized conductors

Some of the most relevant finite-size and surface effects in the magnetic and transport properties of magnetic fine particles and granular solids are reviewed. The stability of the particle magnetization, superparamagnetic regime and the magnetic relaxation are discussed. New phenomena appearing due to interparticle interactions, such as the collective state and non-equilibrium dynamics, are presented. Surface anisotropy and disorder, spin-wave excitations, as well as the enhancements of the coercive field and particle magnetization are also reviewed. The competition of surface and finite-size effects to settle the magnetic behaviour is addressed. Finally, two of the most relevant phenomena in the transport properties of granular solids are summarized namely, giant magnetoresistance in granular heterogeneous alloys and Coulomb gap in insulating granular solids.

https://iopscience.iop.org/article/10.1088/0022-3727/35/6/201/pdf

Finite-size effects in fine particles: magnetic and transport properties

Magnetic sensors can be classified according to whether they measure the total magnetic field or the vector components of the magnetic field. The techniques used to produce both types of magnetic sensors encompass many aspects of physics and electronics. Here, we describe and compare most of the common technologies used for magnetic field sensing. These include search coil, fluxgate, optically pumped, nuclear precession, SQUID, Hall-effect, anisotropic magnetoresistance, giant magnetoresistance, magnetic tunnel junctions, giant magnetoimpedance, magnetostrictive/piezoelectric composites, magnetodiode, magnetotransistor, fiber optic, magnetooptic, and microelectromechanical systems-based magnetic sensors. The usage of these sensors in relation to working with or around Earth's magnetic field is also presented

Magnetic sensors and their applications

Complex perovskite oxides exhibit a rich spectrum of properties, including magnetism, ferroelectricity, strongly correlated electron behaviour, superconductivity and magnetoresistance, which have been research areas of great interest among the scientific and technological community for decades. There exist very few materials which exhibit multiple functional properties; one such class of materials is called the multiferroics. Multiferroics are interesting because they exhibit simultaneously ferromagnetic and ferroelectric polarizations and a coupling between them. Due to the nontrivial lattice coupling between the magnetic and electronic domains (the magnetoelectric effect), the magnetic polarization can be switched by applying an electric field; likewise the ferroelectric polarization can be switched by applying a magnetic field. As a consequence, multiferroics offer rich physics and novel devices concepts, which have recently become of great interest to researchers. In this review article the recent experimental status, for both the bulk single phase and the thin film form, has been presented. Current studies on the ceramic compounds in the bulk form including Bi(Fe,Mn)O3, REMnO3 andthe series of REMn2O5 single crystals (RE =  rare earth) are discussed in the first section and a detailed overview on multiferroic thin films grown artificially (multilayers and nanocomposites) is presented in the second section.

https://iopscience.iop.org/article/10.1088/0953-8984/17/30/R01/pdf

The single-phase multiferroic oxides: from bulk to thin film

We present magnetoresistance experiments in magnetic Ni nanocontacts in the ballistic transport regime at room temperature. It is shown that the magnetoresistance for a few-atom contact reaches values of $280%$ at room temperature and for applied magnetic fields of 100 Oe. Results are presented for over 50 samples showing the trend that the smaller the contact the larger the magnetoresistance response. This indicates that the effect arises just at the nanocontact.

Magnetoresistance in excess of 200% in ballistic ni nanocontacts at room temperature and 100 oe

We present theory and experiments in good agreement for ballistic magnetoresistance in nanoscopic-size contacts in 3 $d$ metals (Ni and Co) It is found that values of the ballistic magnetoconductance of $\ensuremath{\sim}300%$ at room temperature can be explained by scattering by the domain wall which is trapped in the constriction region These values are obtained for very small contacts and they decrease very fast as the contact size increases The theory also explains this behavior

Domain Wall Scattering Explains 300% Ballistic Magnetoconductance of Nanocontacts

We present experimental results of unprecedented large magnetoresistance obtained in stable electrodeposited Ni–Ni nanocontacts 10–30 nm in diameter. The contacts exhibit magnetoresistance of up to 700% at room temperature and low applied fields and, therefore, act as very effective spin filters. These large values of the magnetoresistance are attributed to spin ballistic transport through a magnetic “dead layer” at the contact of width of about 1 nm or smaller. Nanometer sized, high sensitive magnetoresistive sensors could become key elements for magnetic storage in the terabit/in.2 range and in high density magnetic random access memories.

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Ballistic magnetoresistance in a magnetic nanometer sized contact: An effective gate for spintronics

This letter shows that the ballistic magnetoresistance of Fe at room temperature and low magnetic fields is ten times smaller than for Ni and Co. The results are well explained by theory that provides a global understanding for 3d transition metals because, for Fe, the ratio of majority to minority spins at Fermi level is much smaller than for Ni and Co. The data indicate that conduction is carried out by majority d electrons in the case of Fe, in contrast to what happens for Ni and Co.

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Ballistic magnetoresistance in transition-metal nanocontacts: The case of iron

We show that, in a nanometric size stable electrodeposited Ni contact, it is possible to modify the magnetoresistance by applying current pulses and external magnetic fields whereby the same current path is used for detection and modification. We can pass from positive to negative magnetoresistance with values as large as 25% at room temperature, all in the same contact. We propose that the effect may be due to switching and moving domain walls in the contact region under the combination of current effects and external fields.

Y.-W. Zhao

Papers

Magnetoresistance in excess of 200% in ballistic ni nanocontacts at room temperature and 100 oe

Domain Wall Scattering Explains 300% Ballistic Magnetoconductance of Nanocontacts

Ballistic magnetoresistance in a magnetic nanometer sized contact: An effective gate for spintronics

Ballistic magnetoresistance in transition-metal nanocontacts: The case of iron

Negative and positive magnetoresistance manipulation in an electrodeposited nanometer Ni contact.