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

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

The body of research on (III,Mn)V diluted magnetic semiconductors initiated during the 1990's has concentrated on three major fronts: i) the microscopic origins and fundamental physics of the ferromagnetism that occurs in these systems, ii) the materials science of growth and defects and iii) the development of spintronic devices with new functionalities. This article reviews the current status of the field, concentrating on the first two, more mature research directions. From the fundamental point of view, (Ga,Mn)As and several other (III,Mn)V DMSs are now regarded as textbook examples of a rare class of robust ferromagnets with dilute magnetic moments coupled by delocalized charge carriers. Both local moments and itinerant holes are provided by Mn, which makes the systems particularly favorable for realizing this unusual ordered state. Advances in growth and post-growth treatment techniques have played a central role in the field, often pushing the limits of dilute Mn moment densities and the uniformity and purity of materials far beyond those allowed by equilibrium thermodynamics. In (III,Mn)V compounds, material quality and magnetic properties are intimately connected. In the review we focus on the theoretical understanding of the origins of ferromagnetism and basic structural, magnetic, magneto-transport, and magneto-optical characteristics of simple (III,Mn)V epilayers, with the main emphasis on (Ga,Mn)As. The conclusions we arrive at are based on an extensive literature covering results of complementary ab initio and effective Hamiltonian computational techniques, and on comparisons between theory and experiment.

/pdf/theory-of-ferromagnetic-iii-mn-v-semiconductors-24pzayfeji.pdf

Theory of ferromagnetic (III, Mn) V semiconductors

Recent advances in the theory and experimental realization of ferromagnetic semiconductors give hope that a new generation of microelectronic devices based on the spin degree of freedom of the electron can be developed. This review focuses primarily on promising candidate materials (such as GaN, GaP and ZnO) in which there is already a technology base and a fairly good understanding of the basic electrical and optical properties. The introduction of Mn into these and other materials under the right conditions is found to produce ferromagnetism near or above room temperature. There are a number of other potential dopant ions that could be employed (such as Fe, Ni, Co, Cr) as suggested by theory [see, for example, Sato and Katayama-Yoshida, Jpn. J. Appl. Phys., Part 2 39, L555 (2000)]. Growth of these ferromagnetic materials by thin film techniques, such as molecular beam epitaxy or pulsed laser deposition, provides excellent control of the dopant concentration and the ability to grow single-phase layers. T...

/pdf/wide-band-gap-ferromagnetic-semiconductors-and-oxides-48l1gtt253.pdf

Wide band gap ferromagnetic semiconductors and oxides

Microcrystalline Ga1−xMnxN samples with Mn content up to x=0.005 were grown by an ammonothermal method and were studied using various techniques. X-ray diffraction showed characteristic diffraction lines for hexagonal GaN phase mixed with a small contribution (<5%) from the Mn3N2 phase. Raman spectra exhibited characteristic peaks of pure GaN and modes that could be associated with Mn-induced lattice disorder. Electron spin resonance and magnetization measurements were consistent with the dominant Mn2+(d5) configuration of spin S=5/2 which is responsible for the observed paramagnetic behavior of the GaMnN material.

Magnetic and optical properties of GaMnN magnetic semiconductor

Magnetic circular dichroism (MCD) of a ferromagnetic diluted magnetic semiconductor Ga1−xMnxAs films was measured to clarify their electronic structure. Strong enhancement of MCD by Mn substitution indicated a strong sp–d hybridization. The p–d exchange interaction was concluded to be antiferromagnetic, which was in contrast with the reported ferromagnetic p–d exchange in very diluted paramagnetic GaAs:Mn bulk crystals. The change of the character of the p–d exchange interaction is due to the unique feature of Ga1−xMnxAs that the relative abundance of the neutral and ionized Mn acceptors controls the p–d exchange.

Magneto-optic effect of the ferromagnetic diluted magnetic semiconductor Ga1−xMnxAs

The $s,p\ensuremath{-}d$ exchange interaction of p-type ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As} (xl0.05)$ epilayers is investigated by means of magnetoabsorption. The observed ferromagnetic-type splitting of fundamental absorption edge is explained by antiferromagnetic $p\ensuremath{-}d$ exchange interaction, taking into account the Moss-Burstein effect, resulting from high hole concentration.

Antiferromagnetic p-d exchange in ferromagnetic Ga 1-x Mn x As epilayers

The magnetization of Ga1−xMnxN (x<0.1) crystals was measured as a function of the magnetic field and temperature. Paramagnetic behavior typical of spin S=5/2 expected for Mn2+ (d5) magnetic centers was observed in the temperature range of 2 K<T<300 K. On the other hand, antiferromagnetic coupling between Mn ions was clearly visible. The nearest neighbor (NN) coupling constant JNN/kB=−1.9 K was estimated from the temperature dependence of the magnetization.

Andrzej Twardowski

Papers

Magnetic and optical properties of GaMnN magnetic semiconductor

Magneto-optic effect of the ferromagnetic diluted magnetic semiconductor Ga1−xMnxAs

Antiferromagnetic p-d exchange in ferromagnetic Ga 1-x Mn x As epilayers

Paramagnetism and antiferromagnetic d–d coupling in GaMnN magnetic semiconductor

The study of the s-d type exchange interaction in Zn1−xMnxSe mixed crystals