Ferromagnetism in undoped semiconductors
- PDF / 161,208 Bytes
- 5 Pages / 432 x 648 pts Page_size
- 93 Downloads / 251 Views
Ferromagnetism in undoped semiconductors Yandong Ma, Ying Dai* and Baibiao Huang School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, P. R.China ABSTRACT The so-called “d0” magnetism observed in semiconductors, which is not caused by partially filled d orbitals, has challenged our conventional understanding on the origin of magnetism. One class of semiconductor materials showing d0 ferromagnetism is undoped oxides and nitrides. Here, we review the ferromagnetic properties of undoped GaN and MgO based on our recent investigations. It is revealed that the room-temperature ferromagnetism originates from the anion dangling bonds associated with the surface cation-vacancies. And the magnetism of ferromagnetic coupling between the vacancy induced local magnetic moment by through-bond spin polarization in undoped semiconductors is reviewed according to our works. INTRODUCTION Traditionally, considerable attention has been focused on dilute magnetic semiconductors (DMSs), in which local magnetic moments are introduced by doping elements with partially 3d or 4f subshells [1,2]. However, in recent years, “d0” magnetism [3], which is not caused by partially filled d orbitals, has been observed in two classes of semiconductor materials. One consists of nometal doped semiconductors, such as C- or N- doped oxides[4-10] and B- doped AlN and ZnO [11,12], the other is undoped oxides and nitrides as HfO2 [13,14], CaO [15], SnO2 [16], MgO [17] and GaN[18]. Correspondingly, a numerous of theoretical attempts have also been done to explore the mechanism of such new phenomena [19-21]. In this proceeding, we briefly review the previous studies on the electronic structures and the origin of the ferromagnetic coupling between the local spin polarizations induced by vacancy in undoped semiconductors [22,23]. DISCUSSION Ferromagnetism in GaN It has been reported experimentally that GaN nanoparticles exhibit room-temperature “d0” ferromagnetism, which is believed to originate from defects confined on their surface [18]. A theoretical study predicted that Ga-vacancies in bulk GaN give rise to a ferromagnetic ground state [24,25], which makes it be interesting that how surface defects of GaN nanoparticles might cause ferromagnetism with TC over room temperature. Consequently, first-principles DFT calculations are performed to examine the energetic and electronic properties of the bulk and the (10 1 0) surface of GaN containing Ga- and N-vacancies[22]. The calculated energies revealed that the native vacancies favor largely on the surface layer both in bulk and on (101 0) surface of GaN. The electronic structure showed that both Ga-vacancy and N-vacancy induce spinpolarized gap states. However, N-vacancies on the surface cannot account for the observed
99
ferromagnetism in GaN nanoparticles because the unpaired spin is accommodated in the diffuse Ga 4s/4p orbitals leading to the weak interaction of spin polarization. While, each Ga-vacancy leads to a high-spin ground state with magnetic moment of abo
Data Loading...
