Bound magnetic polaron in Cr-based diluted magnetic semiconductors

Herbich, M.; Twardowski, A.; Scalbert, D.; Petrou, A.

doi:10.1103/physrevb.58.7024

Cited by 19 publications

(13 citation statements)

References 36 publications

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“…Thus, in the presence of simultaneous overlap with the localized spins, a macroscopic spin polarization becomes favorable. As discussed in [75], the interaction mechanism of a BMP depends strongly on the configuration of the magnetic ions. The Brillouin-type permanent polarization of the isolated d 5 multiplets of Mn 2+ -and Fe 3+ -based BMPs is determined either by fluctuations in the weak sd coupling regime, or saturates in the strong pd coupling regime.…”

Section: à3mentioning

confidence: 98%

Prospects for carrier‐mediated ferromagnetism in GaN

Graf

Goennenwein

Brandt

2003

Physica Status Solidi (b)

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Theoretical predictions of room-temperature ferromagnetism in Mn-doped GaN and other wide band gap semiconductors suggest that these materials might be useful for spintronic applications. In this short review, we summarize recent observations on the gap states of GaN : Mn, which make it impossible that the two main prerequisites of these predictions can be fulfilled at the same time, which are (1) a large concentration of localized Mn 2þ spins coexisting with (2) a high density of free holes in the valence band. Such conditions have been observed in only a few materials like e.g. GaAs : Mn. More typically, transition-metal impurities act as traps for free carriers, thus pinning the Fermi level in the semiconductor band gap far from the valence or conduction band. Alternatively to ferromagnetism mediated by free carriers, the interactions between bound magnetic polarons and the double-exchange mechanism have been suggested to possibly lead to ferromagnetism in GaN : Mn. Because of the energy position and the character of its gap states, Mn seems to be rather unsuitable for these two mechanisms. Better candidates would be GaN : Fe : Mg for a system of magnetic polarons, and GaN : Cr for a double-exchange ferromagnet. Because of its short-range nature, the double-exchange interaction requires rather concentrated alloys and does not offer significant advantages of GaN : Mn over the established ferromagnetic materials. However, microscopic ferromagnetic inclusions observed in many SQUID measurements of GaN : Mn could possibly help to achieve spin injection in nitride semiconductors. Prerequisites for carrier-mediated ferromagnetismParticularly high Curie temperatures T c have recently been predicted for GaN and other wide band gap semiconductors upon heavy Mn doping [1,2]. Because of the large potential of room-temperature ferromagnetic semiconductors in spintronic devices [3,4], this perspective has triggered significant research activities [5][6][7][8][9][10][11][12][13][14]. According to [1], the magnetic ordering in dilute magnetic semiconductors results from the exchange interaction between localized magnetic spins and delocalized carriers. In particular, the extended wavefunctions of free or weakly bound holes enable a long-range magnetic ordering, which should be adjustable by charge control, e.g. via external gates [15,16], even for low Mn concentrations up to high temperatures. The highest Curie temperatures with T c ! 300 K according to a mean-field Zener model are expected for a d 5 configuration (as found e.g. for Mn 2þ ) and valence-band holes as carriers mediating the magnetic coupling. In GaAs:Mn, the pd exchange energy N 0 b is typically about 1 eV, where N 0 is the concentration of cation sites and b the pd exchange integral between the mostly p-like valence-band states and the mostly d-like Mn 2þ orbitals. It is

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Section: à3mentioning

confidence: 98%

Prospects for carrier‐mediated ferromagnetism in GaN

Graf

Goennenwein

Brandt

2003

Physica Status Solidi (b)

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“…In this diluted regime, carrier mediated spin-coupling could be realized via holes being captured and thermally released by the TM centers [136]. At higher TM concentrations when the average distance becomes equal to the effective Bohr radius, the overlap of the effective-mass-like states enables to mediate ferromagnetic interaction [11,39]. At even higher TM concentrations, the impurity band eventually merges with the VB and the material becomes metallic.…”

Section: Significance Of the [Fementioning

confidence: 99%

“…A good understanding of the electronic structure of all occurring Fe charge states is required for predictions about d-states potentially involved in that hopping process and the formation of such bands. Also the coupling mechanism involving bound magnetic polarons depends crucially on the configuration of the magnetic centers [39].…”

Section: +mentioning

confidence: 99%

Fe in III–V and II–VI semiconductors

Malguth

Hoffmann

Phillips

2008

Physica Status Solidi (b)

114

110

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Many theoretical and experimental studies deal with the realization of room‐temperature ferromagnetism in dilute magnetic semiconductors (DMS). However, a detailed quantitative understanding of the electronic properties of transition metal doped semiconductors has often been neglected. This article points out which issues concerning electronic states and charge transfers need to be considered using Fe as an example. Methods to address these issues are outlined, and a wealth of data on the electronic properties of Fe doped III–V and II–VI compound semiconductors that have been obtained over a few decades is reviewed thoroughly. The review is complemented by new results on the effective‐mass‐like state consisting of a hole bound to Fe2+ forming a shallow acceptor state.The positions of established Fe3+/2+ and Fe2+/1+ charge transfer levels are summarized and predictions on the positions of further charge transfer levels are made based on the internal reference rule. The Fe3+/4+ level has not been identified unambiguously in any of the studied materials. Detailed term schemes of the observed charge states in tetrahedral and trigonal crystal field symmetry are presented including hyperfine structure, isotope effects and Jahn–Teller effect. Particularly, the radiative transitions Fe3+(4T1 → 6A1) and Fe2+(5E → 5T2) are analyzed in great detail.An effective‐mass‐like state [Fe2+, h] consisting of a hole bound to Fe2+ is of great significance for a potential realization of spin‐coupling in a DMS. New insights on this shallow acceptor state could be obtained by means of stress dependent and temperature dependent absorption experiments in the mK range. The binding energy and effective Bohr radius were determined for GaN, GaP, InP and GaAs and a weak exchange interaction between the hole and the Fe2+ center was detected.With regard to the Fe3+ ground state, 6A1, in GaP and InP, the hyperfine structure level Γ8 was found to be above the Γ8 level.All results are discussed with respect to a potential realization of a ferromagnetic spin‐coupling in DMSs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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“…From this it was concluded that the carrierimpurity correlations should in fact be important for the dynamics in DMS. Furthermore, some studies [39][40][41][42][43][44] suggest that bound magnetic polarons can play a key role for the ferromagnetic behaviour of some DMS. These polarons consist of carriers which are bound to the magnetic impurities and, thus, the carriers and impurities are strongly correlated.…”

Section: Introductionmentioning

confidence: 99%

Nonperturbative correlation effects in diluted magnetic semiconductors

2016

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The effects of carrier-impurity correlations due to a Kondo-like spin-spin interaction in diluted magnetic semiconductors are investigated. These correlations are not only responsible for a transfer of spins between the carriers and the impurities, but also produce non-perturbative effects in the spin dynamics such as renormalization of the precession frequency of the carrier spins, which can reach values of several percent in CdMnTe quantum wells. In two-dimensional systems, the precession frequency renormalization for a single electron spin with defined wave vector shows logarithmic divergences similar to those also known from the Kondo problem in metals. For smooth electron distributions, however, the divergences disappear due to the integrability of the logarithm. A possible dephasing mechanism caused by the wave-vector dependence of the electron spin precession frequencies is found to be of minor importance compared to the spin transfer from the carrier to the impurity system. In the Markov limit of the theory, a quasi-equilibrium expression for the carrier-impurity correlation energy can be deduced indicating the formation of strongly correlated carrier-impurity states for temperatures in the mK range.

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Bound magnetic polaron in Cr-based diluted magnetic semiconductors

Cited by 19 publications

References 36 publications

Prospects for carrier‐mediated ferromagnetism in GaN

Prospects for carrier‐mediated ferromagnetism in GaN

Fe in III–V and II–VI semiconductors

Nonperturbative correlation effects in diluted magnetic semiconductors

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