We review the physical properties of diluted magnetic semiconductors (DMS) of the type AII1−xMnxBVI (e.g., Cd1−xMnxSe, Hg1−xMnxTe). Crystallographic properties are discussed first, with emphasis on the common structural features which these materials have as a result of tetrahedral bonding. We then describe the band structure of the AII1−xMnxBVI alloys in the absence of an external magnetic field, stressing the close relationship of the sp electron bands in these materials to the band structure of the nonmagnetic AIIBVI ‘‘parent’’ semiconductors. In addition, the characteristics of the narrow (nearly localized) band arising from the half‐filled Mn 3d5 shells are described, along with their profound effect on the optical properties of DMS. We then describe our present understanding of the magnetic properties of the AII1−xMnxBVI alloys. In particular, we discuss the mechanism of the Mn++‐Mn++ exchange, which underlies the magnetism of these materials; we present an analytic formulation for the magnetic susc...

Diluted magnetic semiconductors

General analysis of magnetic refrigeration and its optimization using a new concept: maximization of refrigerant capacity

This paper reviews the electrical, magnetic, and optical properties of diluted magnetic semiconductors (sometimes also referred to as ‘‘semimagnetic’’ semiconductors). These materials are ternary semiconductor alloys whose lattice is made up in part of substitutional magnetic ions. Cd1−xMnxTe and Hg1−xMnxTe are examples of such systems. As semiconductors, these alloys display interesting and important properties, such as the variation of the energy gap and of effective mass with composition. They also exhibit magnetic properties which are interesting in their own right, e.g., a low temperature spin glass transition and magnon excitations. Most importantly, however, the presence of substitutional magnetic ions in these alloys leads to spin–spin exchange interaction between the localized magnetic moments and the band electrons. This in turn has rather important consequences on band structure and on donor and acceptor states, leading to dramatic effects in quantum transport, impurity conduction, and magneto‐optics. Specifically, the presence of exchange interaction results in extremely large and temperature dependent g‐factors of electrons and holes; in gigantic values of Faraday rotation; in anomalously large negative magnetoresistance; and in the formation of the bound magnetic polaron.

Diluted magnetic semiconductors: An interface of semiconductor physics and magnetism (invited)

Reviewed at both a relatively elementary and more advanced level is the interpretative theory of the electron spin resonance of magnetic ions in metals. The various theoretical possibilities are illustrated by experimental examples wherever possible. Initially the development is based upon the Bloch-Hasegawa equations. The relationship of the advanced theory to this more elementary theory is emphasized. Multimagnetic-impurity experiments, the skin depth problem, the analysis of exchange, hyperfine and crystal field parameters, Redfield theory, ionic and virtual bound state models and the Kondo effect, all in relation to E.S.R. in metals, are each covered in some detail. A discussion of some outstanding problems and projections for the future are also included.

Theory of electron spin resonance of magnetic ions in metals

Optical Properties of (Zn, Mn) and (Cd, Mn) Chalcogenide Mixed Crystals and Superlattices

We have measured the magnetic susceptibility and the electron paramagnetic resonance for ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Te}(0.001\ensuremath{\le}x\ensuremath{\le}0.60)$ and ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Se}(0.001\ensuremath{\le}x\ensuremath{\le}0.45)$ as a function of magnetic field, temperature, time, and microwave frequency. For $xl0.20$, both systems remain paramagnetic for all temperatures measured ($0.7\ensuremath{\le}T\ensuremath{\le}300$ K). Above $x\ensuremath{\simeq}0.20$, a cusp in the low-field susceptibility after zero-field cooling was observed at a temperature ${T}_{f}$, its position being a linear function of concentration. A broadening and a shift in the magnetic field of the electron paramagnetic resonance line with decreasing temperature were observed, and found to be independent of the microwave frequency used (9 and 35 GHz). The isothermal remanent and thermoremanent magnetization were studied in detail. The magnetic properties of these systems are similar to those of the canonical metallic spin-glasses, with the exception that the scaling law for the magnetization is not obeyed.

Magnetic susceptibility and EPR measurements in concentrated spin-glasses: Cd 1 − x Mn x Te and Cd 1 − x Mn x Se

Magnetic measurements on Al‐flux grown EuB6 crystals show that this material orders ferromagnetically with a transition temperature Tc=13.7 K. The effective moment derived from paramagnetic susceptibility measurements gives μeff=7.76 μB, and the saturation magnetization extrapolated to 0 K is within 10% of the theoretical value of 7 μB expected for Eu+2. The magnetic order, however, cannot be that of a simple colinear ferromagnet because the magnetic specific heat in zero applied magnetic field shows a broad maximum centered about 9 K rather than the expected λ‐like anomaly at 13.7 K. Finally, transport measurements suggest that EuB6 is an intrinsic semimental.

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Magnetic, transport, and thermal properties of ferromagnetic EuB6

EPR experiments have been performed in l‐alanine single crystals doped with copper in order to measure the gyromagnetic tensor of Cu(ii) and the hyperfine coupling tensor with 63Cu. The hyperfine coupling and the nuclear quadrupole interaction tensors of a ligand nitrogen have been obtained by ENDOR at 4 K. The principal values of the hyperfine coupling of 14N are: AN(1)=27 190 KHz, AN(2)=27 560 KHz, and AN(3)=41 740 KHz and those for the nuclear quadrupole interaction are PN(1)=97 KHz, PN(2)=987 KHz and PN(3)=−1084 KHz. The principal directions of the four tensors evaluated in this work are noncoincident. ENDOR resonances of another nitrogen ligand and at least three protons have been detected. Our ENDOR measurements show a pseudonuclear spin–spin interaction between 63Cu and 14N nuclei. This effect is very large and arises from a high order mechanism involving the hyperfine couplings of the unpaired electrons of Cu(ii) with those nuclei. The data are explained with a second order perturbation calculation and it is shown that these effects should be considered in systems with low symmetry where the electrons are coupled to more than one magnetic nuclei.

EPR and ligand‐ENDOR measurements of Cu (ii) in l‐alanine single crystals

We have performed electron paramagnetic resonance measurements in single crystals of Cd1−xMnxTe at 9 GHz between 1.6 and 290 K for a wide range of manganese content (0.0005?x?0.60). The temperature of the order‐disorder transition, Tc, and the critical exponent α, were determined from the temperature dependence of the EPR linewidth. At x=0.2 we find a discontinuity in Tc suggestive of a percolation critical point.

S. Oseroff

Papers

Magnetic susceptibility and EPR measurements in concentrated spin-glasses: Cd 1 − x Mn x Te and Cd 1 − x Mn x Se

Magnetic, transport, and thermal properties of ferromagnetic EuB6

EPR and ligand‐ENDOR measurements of Cu (ii) in l‐alanine single crystals

Electron spin resonance in Cd1−xMnxTe

Magnetic properties of Cd1−xMnxTe