Magnetic polarons

A.K. Ramdas and S. Rodriquez, Raman Scattering in Diluted Magnetic Semiconductors P.A. Wolff, Theory of Bound Magnetic Polarons in Semimagnetic Semiconductors... 

The interaction between a charged point defect and neighboring magnetic ions in magnetically doped thin films has been described in terms of a defect cluster called a bound magnetic polaron (Fig. 9.5a). The radius of a bound magnetic polaron due to an electron located on the defect, r, is given by... 

Figure 9.5 Schematic representation of a bound magnetic polaron (a) one bound magnetic polaron located on a charged defect and (b) overlapping bound magnetic polarons leading to ferromagnetic alignment of magnetic ions.

Co0.04Zn0.96O is a ferromagnetic semiconductor, (a) Estimate the radius of a bound magnetic polaron in this material, (b) If the Co2+ ions are uniformly... 

Diet T, Spalek J (1982) Effect of Fluctuations of Magnetization on the Bound Magnetic Polaron - Comparison with Experiment. Phys Rev Lett 48 355-358... 

A rather large negative MR, with a substantial anisotropy, has been observed in reentrant insulating samples with high x (Oiwa et al. 1998b Katsumoto et al. 1998). A destruction of bound magnetic polarons, as invoked in an earlier work on (In.Mn)As... 

Magnetostriction measurements have also been interpreted as proof for the existence of magnetic polarons above Tq in La2/3Sri/3Mn03 perovskites (De Teresa et al. 1997). See below, however, for an alternate interpretation, as discussed by Demin et al. (1997) and others. 

Fig.4 Magnetic polaron (big shaded region) for the rectangular strip with N=L+1.

Fig. 6. Magnetic polarons (big shaded regions) for different values of electron concentration p in the interval 1 ln< p <21 n. The small ellipses correspond to the two-electron states of the segments.

As a result we have obtained the effective Hamiltonian with the two types of interaction of neighboring segments. The competition between these types of interactions leads to the formation of a magnetic polaron similar to the anisotropic one band U=oo Hubbard model. 

Fig. 12 Complexity of the problem of marginal metallicity (adapted from ref. 27). The oxides discussed in this article fall somewhere in the three-dimensional space indicated here. The other factors include electron-lattice interaction, magnetic polaron and finite temperature effects.

The tSR data are compatible with either dense spin glass freezing or with the sudden condensation of a coherent Kondo state (for a discussion see, for example, Grewe and Steglich 1991) with slow, but dynamic spin correlations at 2.5K. The latter interpretation ties in with the specific heat data, especially in applied fields. The former could be explained in terms of the magnetic polaron model formulated by Kasuya et al. (1993a,b). 

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