Curie temperature of ferromagnetic (Ga,Mn)N epitaxial films

Abstract

PACS 75.47.Pq, 75.50.Pp, 81.15.Hi Electron-mediated ferromagnetism persisting to room temperature has been investigated in epitaxial (Ga,Mn)N films with low Mn concentration grown by plasma-enhanced molecular beam epitaxy (PEMBE).The experimental value of T C (~325 K) in the (Ga,Mn)N film with x = 0.3% from the difference (∆M) between field-cooled (FC) and zero field-cooled (ZFC) magnetization curves is found to be lower than the estimated value of T C (~407 K), obtained by the mean field approximations. The extra-ordinary Hall effect in the epitaxial (Ga,Mn)N film with x = 0.2% is found to appear in the temperature range 100 K -300 K. [1] predicted on the basis of the mean-field Zener model of ferromagnetism that the Curie temperature (T C ) for GaN and ZnO can be higher than room temperature, wide bandgap semiconductors are of central importance in the search for novel diluted magnetic semiconductors (DMSs). In particular, the recent discovery of ferromagnetic ordering in Mn-doped GaN semiconductors with T C exceeding room temperature has generated intense interest in spintronics for device applications [2 -6]. Although the Curie temperature in the GaMnN system has been estimated by mean field theoretical considerations, the empirical determination of the Curie temperature still remains controversial [2 -6].In this article, we report on electron-induced ferromagnetism persisting to above room temperature in epitaxial (Ga,Mn)N films grown by plasma-enhanced molecular beam epitaxy (PEMBE). We find that T C in the (Ga,Mn)N film with x = 0.3% was estimated to be ∼407 K by fitting the M-T curve with theoretical equations based on the mean field theory. However, the experimental value of T C was observed to be ∼325 K from the temperature dependence of the magnetization difference ∆M = (M FC -M ZFC ) between field-cooled (FC) and zero field-cooled (ZFC) magnetization curves. We discuss the implication of the mean field approximations and experimental results on the Curie temperature in detail.