Double-exchange mechanisms for Mn-doped III-V ferromagnetic semiconductors

Abstract

A microscopic model of indirect exchange interaction between transition metal impurities in dilute magnetic semiconductors (DMS) is proposed. The hybridization of the impurity delectrons with the heavy hole band states is largely responsible for the transfer of electrons between the impurities, whereas Hund rule for the electron occupation of the impurity d-shells makes the transfer spin selective. The model is applied to such systems as n−type GaN:Mn and p−type (Ga,Mn)As, p−type (Ga,Mn)P. In n−type DMS with Mn 2+/3+ impurities the exchange mechanisms is rather close to the kinematic exchange proposed by Zener for mixed-valence Mn ions. In p−type DMS ferromagnetism is governed by the kinematic mechanism involving the kinetic energy gain of heavy hole carriers caused by their hybridization with 3d electrons of Mn 2+ impurities. Using the molecular field approximation the Curie temperatures T C are calculated for several systems as functions of the impurity and hole concentrations. Comparison with the available experimental data shows a good agreement.

Ferromagnetism in Gd doped ZnO nanowires: A first principles study

“…The double-exchange model is based on a physical picture of the d electron hopping between atoms with strong on-site exchange. 34 In the present study of ZnO:Gd nanowires, V O donates two electrons to the system, mediating the ferromagnetic exchange and hence, the s-f coupling is more prominent than other mechanisms. 34,35 According to our calculations, introducing V Zn does not increase the ferromagnetic coupling energy.…”

“…34 In the present study of ZnO:Gd nanowires, V O donates two electrons to the system, mediating the ferromagnetic exchange and hence, the s-f coupling is more prominent than other mechanisms. 34,35 According to our calculations, introducing V Zn does not increase the ferromagnetic coupling energy. Moreover, p-f exchange interaction mediated by holes is not possible, as the calculated DOS of Gd-doped ZnO nanowire shows a shift of Fermi level towards the conduction band, implying that electrons can mediate FM through s-f interactions.…”

“…Since d orbitals are not contributing to the partially filled energy bands, the double exchange picture is inappropriate for describing the exchange interaction in the current context of ZnO:Gd nanowires. 34 In this case, when Fermi level overlaps with the Gd f-state (which becomes partially filled) donor electrons occupy empty f states and thus FM coupling occurs. 23 The type of carriers involved in establishing long-range ferromagnetic order determines the exchange interactions in DMS materials.…”

Character of states near the Fermi level in (Ga,Mn)As: Impurity to valence band crossover

“…1 and generally accepted for the shallow acceptor counterparts to GaAs:Mn, applies well to the intermediate extrinsic GaAs:Mn. The perception of merged impurity and valence bands in highly Mn-doped metallic GaAs is now also firmly established in the microscopic theory community 7,15,[18][19][20][21][22] and provides a qualitative, and often a semiquantitative, description of micromagnetic and magnetotransport characteristics of bulk and microstructured ͑Ga,Mn͒As ferromagnets. 6,7,15 Our paper, which we believe further establishes the valence-band nature of the Fermi level states in metallic GaAs:Mn, is timely as the topic is still not fully settled.…”

Third-order many-body perturbation theory applied to Kondo-type dynamics in diluted magnetic semiconductors

“…In Ref. 19 it is shown that doubleexchange and superexchange mechanisms can play an important role on the static polarization of a DMS. According to these considerations the present work is addressed to the study of the third-order exchange contributions and its influence on the time evolution of the total magnetization in a DMS.…”