Hall Effect and Magnetoresistance in P-Type Ferromagnetic Semiconductors

Abstract

Recent works aiming at understanding magnetotransport phenomena in ferromagnetic III-V and II-VI semiconductors are described. Theory of the anomalous Hall effect in p-type magnetic semiconductors is discussed, and the relative role of side-jump and skew-scattering mechanisms assessed for (Ga,Mn)As and (Zn,Mn)Te. It is emphasized that magnetotransport studies of ferromagnetic semiconductors in high magnetic fields make it possible to separate the contributions of the ordinary and anomalous Hall effects, to evaluate the role of the spins in carrier scattering and localization as well as to determine the participation ratio of the ferromagnetic phase near the metal-insulator transition. A sizable negative magnetoresistance in the regime of strong magnetic fields is assigned to the weak localization effect.

Role of defects in ferromagnetism inZn1−xCoxO: A hybrid density-functional study

“…Disproportionation of magnetic, singly charged vacancies into nonmagnetic neutral and doubly charged vacancies seems to preclude simple oxygen vacancies from being the mediator of ferromagnetism in Zn 1−x Co x O. The mechanism of exchange coupling is discussed and compared to that proposed by Dietl et al 65 The differences in the models for exchange coupling described here lie in the degree of localization of the magnetic state responsible for exchange coupling ͑determined by the acceptor binding energies͒ and positions of their centroids ͑on the transition metal for the model of Dietl et al or …”

“…A mechanism of exchange coupling has been proposed by Dietl et al 65 to account for ferromagnetism in zinc-blende semiconductors, particularly Ga 1−x Mn x As; Mn 2+ 3d 5 ions substitute for Ga 3+ ions and so introduce a shallow acceptor state with a binding energy of order 100 meV. 65 The key elements of this mechanism are an unpaired electron in the valence band whose wave function overlaps that of the transition-metal ion and whose spin is opposite to that of the transition-metal ion.…”

“…65 The key elements of this mechanism are an unpaired electron in the valence band whose wave function overlaps that of the transition-metal ion and whose spin is opposite to that of the transition-metal ion. In the particular case of Ga 1−x Mn x As, a 2+ ion is substituted for a 3+ ion, so that the substitution simultaneously produces a transition-metal ion magnetic moment and an unpaired electron state with appropriate spin.…”

Effects of Ni implantation into bulk and epitaxial GaP on structural and magnetic characteristics

“…In Mndoped GaAs and InAs for example, the transition temperatures are very low (B/105 K). Since the Curie temperature is predicted to be a strong function of bandgap, magnetic ion concentration and carrier concentration in the semiconductor, it has been proposed that materials with gaps much larger than GaAs and InAs should be investigated [9]. There has been some success in initial experiments on (Ga,Mn)N, prepared either by bulk growth processes [10,11] or direct implantation of Mn into GaN [12,13].…”

“…This study enabled the comparison between the magnetic properties in the presence of either electrons or holes. This is important for determining the origin of ferromagnetism in dilute magnetic semiconductors since it is carrier-mediated and may work only with p-type material [9]. Our results show two contributions to the ferromagnetism in both types of Ni-implanted GaP, one which is present below Â/75 K and the other which remains until Â/225 K. No evidence of secondary phase formation was found by selected area diffraction pattern analysis or by transmission electron microscopy (TEM).…”