The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

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

Ferromagnetism in manganese compound semiconductors not only opens prospects for tailoring magnetic and spin-related phenomena in semiconductors with a precision specific to III-V compounds but also addresses a question about the origin of the magnetic interactions that lead to a Curie temperature (T(C)) as high as 110 K for a manganese concentration of just 5%. Zener's model of ferromagnetism, originally proposed for transition metals in 1950, can explain T(C) of Ga(1-)(x)Mn(x)As and that of its II-VI counterpart Zn(1-)(x)Mn(x)Te and is used to predict materials with T(C) exceeding room temperature, an important step toward semiconductor electronics that use both charge and spin.

http://info.ifpan.edu.pl/SL-2/sl23sub/science_dietl.pdf

Zener Model Description of Ferromagnetism in Zinc-Blende Magnetic Semiconductors

REVIEW Semiconductor devices generally take advantage of the charge of electrons, whereas magnetic materials are used for recording information involving electron spin. To make use of both charge and spin of electrons in semiconductors, a high concentration of magnetic elements can be introduced in nonmagnetic III-V semiconductors currently in use for devices. Low solubility of magnetic elements was overcome by low-temperature nonequilibrium molecular beam epitaxial growth, and ferromagnetic (Ga,Mn)As was realized. Magnetotransport measurements revealed that the magnetic transition temperature can be as high as 110 kelvin. The origin of the ferromagnetic interaction is discussed. Multilayer heterostructures including resonant tunneling diodes (RTDs) have also successfully been fabricated. The magnetic coupling between two ferromagnetic (Ga,Mn)As films separated by a nonmagnetic layer indicated the critical role of the holes in the magnetic coupling. The magnetic coupling in all semiconductor ferromagnetic/nonmagnetic layered structures, together with the possibility of spin filtering in RTDs, shows the potential of the present material system for exploring new physics and for developing new functionality toward future electronics.

https://science.sciencemag.org/content/sci/281/5379/951.full.pdf

Making Nonmagnetic Semiconductors Ferromagnetic

The current status of research on the carrier-mediated ferromagnetism in tetrahedrally coordinated semiconductors is briefly reviewed. The experimental results for III–V semiconductors, where Mn atoms introduce both spins and holes, are compared to the case of II–VI compounds, in which the ferromagnetism has been observed for the modulation-doped p-type Cd1−xMnxTe/Cd1−y−zMgyZnzTe:N heterostructures, and more recently, in Zn1−xMnxTe:N epilayers. On the theoretical side, a model is presented, which takes into account: (i) strong spin–orbit and kp couplings in the valence band; (ii) the effect of confinement and strain upon the hole density-of-states and response function, and (iii) the influence of disorder and carrier–carrier interactions, particularly near the metal-to-insulator transition. A comparison between the experimental and theoretical results demonstrates that the model can describe the magnetic circular dichroism, the values of TC observed in the studied systems as well as explain the directions of the easy axis and the magnitudes of the corresponding anisotropy fields as a function of confinement and biaxial strain. Various suggestions concerning design of novel ferromagnetic semiconductor systems are described.

Ferromagnetism in III-V and II-VI Semiconductor Structures

Mesoscopic phenomena in nanostructures that incorporate diluted magnetic semiconductors may exhibit a number of novel features driven by spin interactions between mobile electrons and localized spins. Millikelvin studies of linear and nonlinear diffusive charge transport, which have been carried out for submicron wires of epilayers as well as for microstructures of bicrystals, are reviewed. These studies have provided information on the significance of spin-disorder scattering and evidence of a new driving mechanism of the magnetoconductance fluctuations - the redistribution of the electrons between energy levels of the system, induced by the giant s - d exchange spin-splitting. Important implications of these findings for previous interpretations of spin effects in semiconductor and metal nanostructures are discussed.

http://iopscience.iop.org/article/10.1088/0268-1242/11/11S/029/pdf

Universal conductance fluctuations in submicron wires of

Microscopic four-contact probes to semimagnetic HgCdMnTe grain-boundary inversion 1ayers have been photolithographically patterned. Magnetoresistance measurements performed on these samples revealed aperiodic conductance fluctuations of the magnitude of the order of e2 /h. Quantitative analysis of both fluctuation amplitude and their mean period indicate that we have approached the mesoscopic regime in our system. This opens new possibilities in studies of spin-subsystem dynamics in semimagnetic semiconductors.

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Conductance Fluctuations in Microstructures of HgCdMnTe Bicrystals

Theoretical description of spin waves in the p‐d Zener model of a dilute magnetic semiconductor in Ref [1] allowed us to discover new effects resulting from spatial inversion asymmetries. In this paper, we focus on thin layers and bulk crystals of (Ga,Mn)As, as described by the spdsf* tight‐binding computational scheme. We demonstrate how the Dzyaloshinskii‐Moriya interaction in thin layers leads to the formation of a zero‐temperature spin cycloid and the accompanying uniaxial anisotropy of in‐plane diagonal ([110]/[110]) directions. We also investigate the exchange stiffness with its anisotropic part, which accounts for the elliptical polarization of longitudinal spin waves—kinetically, their Lorentz contraction in the direction of motion. Additionally, a model for the spin‐wave contribution to magnetization and Curie temperature is proposed. Our theory is applied and compared to relevant experimental data gathered during the recent years.

Theory of spin waves in ferromagnetic (Ga,Mn)As

SQUID measurements of the time decay of the thermoremanent magnetization (field-cooled in 1000 Oe) at long time scale, 102 < t < 105 s, are presented for MBE grown Cd 0.50 Mn 0.50 Τe. We found that for both thin (32 A) and thick (2500 A) layers the spin-glass dynamics is characterized by a similar value of k = -(1/Tf)(dTf/dlog t) > 0.05, indicating the absence of the phase transition at nonzero temperature under the experimental conditions.

http://przyrbwn.icm.edu.pl/APP/PDF/90/a090z5p15.pdf

Tomasz Dietl

Papers

Ferromagnetism in III-V and II-VI Semiconductor Structures

Universal conductance fluctuations in submicron wires of

Conductance Fluctuations in Microstructures of HgCdMnTe Bicrystals

Theory of spin waves in ferromagnetic (Ga,Mn)As

Search for Dimensionality Crossover of Spin-Glass Freezing in Superlattices of Cd0.50Mn0.50Te/CdTe