Physical origin of the ferromagnetic ordering above room temperature in GaMnN nanowires

Abstract

We report a new method for large-scale production of GaMnN nanowires, by annealing manganese-gallium oxide nanowires in flowing ammonia at high temperature. Microstructure analysis indicates that the GaMnN nanowires have wurtzite GaN structure without Mn precipitates or Mn-related second phases. Magnetic measurements reveal that ferromagnetic ordering exists in the GaMnN nanowires, whose Curie temperature is above room temperature. A mean-field model based on the exchange coupling of the nondegenerate carrierlocalized impurity band, together with the consideration of the superexchange antiferromagnetic interaction, is used to explain the physical origin of the observed ferromagnetic ordering. Theoretical calculations indicate that the Curie temperature increases with the increase of the hole density and reveal a small ratio of the hole to the magnetic dopant density in the samples. The low ratio of hole to Mn concentration and the superexchange antiferromagnetic interaction lead to the very concave temperature dependence of the magnetization curve in contrast to conventional ferromagnetic M-T behaviour. The theoretical calculation is in agreement with the experimental data.Recently, diluted magnetic semiconductors (DMSs) have attracted considerable attention since they manifest both the spin and charge properties of the carriers, and much effort has been devoted to spintronics from the viewpoint of fundamental physics and potential applications. A high-Curie-temperature DMS above room temperature is the key for applications. A breakthrough theoretical work reported that some wide-bandgap semiconductors such as GaN and ZnO are the most promising candidates for achieving practical ferromagnetic ordering with T c above room temperature [1,2]. Much work has then focused on the Mnbased II-VI and III-V semiconductor materials, such as GaMnAs, InMnAs, GaMnN and

Hole mediated magnetism in Mn-doped GaN nanowires

“…4, i.e., all the peaks are fully merged by the thermal distribution of holes in the valence band as T C is very high. 22,23 Mn-doped GaN nanowires have promising applications in information processing and spintronics; for example, they can be used as quantum conducting wires in quantum circuits. In this high x eff case, T C is not sensitive to the detailed band structure (i.e., maximums of hole subbands), thus the difference between T C versus p plots of cylindrical nanowires and ribbons is small.…”

“…: Condens. [21][22][23] Hole-mediated ferromagnetism in single-crystalline wurtzite-structured Mn-doped GaN nanowires with T C in excess of 300 K has been observed in experiments. The ferromagnetism in Mn-doped GaN wire is slightly anisotropic due to the small spin-orbit coupling.…”

“…Matter 17, 5073 (2005)]. 22,23 In the mean-field theory, the ferromagnetism in DMSs is approximately proportional to the density of states around the Fermi level. V C 2011 American Institute of Physics.…”

Structure and Elemental Distribution of (Ga,Mn)N Nanowires

“…Experimentally, the magnetic properties of (Ga,Mn)N NWs grown by various methods have been reported to vary between paramagnetic and ferromagnetic up to room temperature. [4][5][6][7][8][9][10] In some reports also the distribution of Mn has been investigated and is found to be homogeneous within the NWs. 4,7,[9][10][11][12] In this Letter we report on the growth of (Ga,Mn)N NWs by molecular beam epitaxy (MBE) with the main focus on the structural and chemical composition which could play an important role in determining the magnetic properties as already pointed out above.…”

“…[4][5][6][7][8][9][10] In some reports also the distribution of Mn has been investigated and is found to be homogeneous within the NWs. 4,7,[9][10][11][12] In this Letter we report on the growth of (Ga,Mn)N NWs by molecular beam epitaxy (MBE) with the main focus on the structural and chemical composition which could play an important role in determining the magnetic properties as already pointed out above. The NWs all grow in the stable wurtzite structure, and Mn is preferentially incorporated at the surface.…”