Magnetic Defects

Accurate experimental determinations require that not only the handedness of the produced light, but its exact degree of polarization, are known. The theoretical performance of an undulator may be in practice be degraded by magnetic defects, and the optical beam can be further depolarized by reflections along the beamline. Again, the dephasing on optical elements can in principle be... 

Magnetic defects can be thought of as defects in the magnetic dipole state of an atom or group of atoms compared to those of the parent structure. For instance, magnetic defects can be considered to form when magnetic ions are introduced into a nonmagnetic structure, either as substituents or as interstitials (Fig. 9.1a and 9.1b). These... 

Figure 9.1 Schematic representation of magnetic defects in a nonmagnetic matrix (a) impurity substituent and (b) impurity interstitial.

Figure 9.2 Schematic representation of magnetic defects in a magnetic matrix (a) vacancy or nonmagnetic impurity, (b) self-interstitial, (c) magnetic Frenkel defect , (d) magnetic foreign substituent, and (e) magnetic foreign interstitial. The magnetic matrix can have ordered (as drawn) or disordered spins.

Neither the magnetic defect structures of these phases nor the mechanism of the CMR effect are yet clear, although Mn3+-Mn4+ interactions are believed to be important in inducing CMR. 

Figure 9.9 Magnetic defects in FeO (a) antiferromagnetic alignment of magnetic moments in nominally stoichiometric FeO with the spins perpendicular to [111] (Z>) the simplest defect cluster in FeO, with the spin on the interstitial Fe lying in (111) and (c) antiferromagnetic coupling of the surrounding Fe ions with all spins lying in (111).

In the initial state, all transition-metal ions are in the low-spin state, giving an effectively nonmagnetic solid. Irradiation transfers an electron from Fe to Co and promotes electron excitation to create all high-spin ions with a considerable magnetic moment (Fig. 9.29b). The magnetic defects in this case are the triple group of metal ion-cyanide-metal ion. As in all materials for device use, variation in dopant concentrations can be used to tune the desirable properties of the solid. 

R93 J. A. Weil, A Demi-Century of Magnetic Defects in a-Quartz , p. 197... 

Levin (1979) has studied the ternary compound CeCo2Si2. He reported the dependence of the spontaneous Hall effect and the magneto-resistance on the applied field. He observed anomalous galvanomagnetic effects due to an asymmetric distribution of charge carriers caused by their spin-orbit interaction with magnetic defects (Co clusters). 

Fig. 4.18 Dependence of the exchange integral J on the distance r between the magnetic defects for permittivity 6 = 30, 100, 300 (figures near the curves) [48]...

Therefore undoped nanoparticles (size< 10-100 nm) of incipient ferroelectrics could become ferromagnetic up to the room temperatures due to the inherent presence of a new type of magnetic defects — oxygen vacancies, where the... 

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