Diluted Ferromagnetic Semiconductors—Theoretical Aspects

Abstract

This chapter reviews theoretical understanding of ferromagnetic response that has been detected in diluted magnetic semiconductors (DMS). Particular attention is paid to those ferromagnetic DMS in which no precipitation of other crystallographic phases has been observed. It is argued that these materials can be divided into three categories. The first consists of (Ga,Mn)As, heavily doped p‐(Zn,Mn)Te, and related compounds. In these solid solutions, the theory built on p–d Zener's model of hole‐mediated ferromagnetism and on either the Kohn‐Luttinger kp theory or the multiorbital tight‐binding approach describes qualitatively, and often quantitatively, thermodynamic, micromagnetic, optical, and transport properties. Moreover, the understanding of these materials has provided a basis for the development of novel methods enabling magnetization manipulation and switching. To the second group, belong compounds in which a competition between long‐range ferromagnetic and short‐range antiferromagnetic interactions and/or the proximity of the localization boundary lead to an electronic nanoscale phase separation that results in characteristics similar to colossal magnetoresistance oxides. Finally, in a number of compounds a chemical nanoscale phase separation into the regions with small and large concentrations of the magnetic constituent is present. Methods of controlling the spinodal decomposition and possible functionalities of these systems are outlined.

Origin of ferromagnetic response in diluted magnetic semiconductors and oxides

“…These materials exhibit characteristics specific to both charge transfer insulators and strongly correlated disordered metals. Moreover, complexities specific to strongly correlated systems coexist in DMSs with features exhibited by heavily doped semiconductors and semiconductor alloys, such as Anderson-Mott localization [9], defect generation by self-compensation mechanisms [70,71,51], and the breakdown of the virtual crystal approximation [72]. Nevertheless, the theory built on the p-d Zener model of carriermediated ferromagnetism and on either Kohn-Luttinger's kp [69,70,73] or multi-orbital tightbinding [74][75][76] descriptions of the valence band in tetrahedrally coordinated semiconductors has qualitatively, and often quantitatively, described thermodynamic, micromagnetic, transport, and optical properties of DMSs with delocalized holes [77][78][79], challenging competing theories.…”

“…Here, two approaches have been pursued. The first of them, initiated by Gała ¸zka et al [7][8][9] and by Ohno et al [10][11][12], is the incorporation of magnetism into functional semiconductors by alloying with transition metals, notably Mn. To date, a ferromagnetic response, often persisting to above room temperature, has been detected in a large number of semiconductor and oxide thin layers containing a minute number of magnetic ions [13,14] or even nominally undoped by magnetic elements [15].…”

Photo-Induced Spin Dynamics in Nanoelectronic Devices

“…[6−8] Diluted magnetic semiconductors of II-VI compounds have attracted a considerable attention for the last few years due to the carrier-mediated origin of the ferromagnetism. [9] This special feature makes it possible to control quantization of the material by changing the concentration of the carriers, which is required property for future applications in semiconductor spintronics and in optoelectronic devices. [9,10] The II-VI diluted magnetic semiconductors are known to be good candidates for effective spin injection into a nonmagnetic semiconductor because their spin polarization can be easily detected.…”

“…[9] This special feature makes it possible to control quantization of the material by changing the concentration of the carriers, which is required property for future applications in semiconductor spintronics and in optoelectronic devices. [9,10] The II-VI diluted magnetic semiconductors are known to be good candidates for effective spin injection into a nonmagnetic semiconductor because their spin polarization can be easily detected. [11,12] Quantum dots are semiconductor heterostructures in which carriers are confined in all three space dimensions.…”

Dilute Magnetic Semiconductors

“…magnetic circular dichroism (MCD) [32], and resistivity measurements above the critical temperature [33], indicate an anti-ferromagnetic coupling between the local 3d 5 electrons and the valence holes. This so-called kinetic-exchange interactions originates from the hybridization between the Mn 3d-orbitals and the neighboring As 4p-orbitals and is much larger than the pure Coulomb exchange interaction [34]. e) In transport measurements, a large anomalous-Hall effect (AHE) completely dominates the low-field off-diagonal resistance coefficient.…”