Magnetization study of nanograined pure and Mn-doped ZnO films: Formation of a ferromagnetic grain-boundary foam

Abstract

In order to elucidate room-temperature ͑RT͒ ferromagnetism ͑FM͒ in ZnO, we have analyzed a multitude of experimental publications with respect to the ratio of grain-boundary ͑GB͒ area to grain volume. FM only appears if this ratio exceeds a certain threshold value s th . Based on these important results nanograined pure and Mn-doped ZnO films have been prepared, which reveal reproducible RT FM and magnetization proportional to the film thickness, even for pure ZnO films. Our findings strongly suggest that grain boundaries and related vacancies are the intrinsic origin for RT ferromagnetism.

Magnetism in Dopant-Free ZnO Nanoplates

“…Therefore, the magnitude of the saturation magnetization is in the order of 10 −1 emu/g, which is much larger than the moments of ZnObased dilute magnetic semiconductors doped with magnetic atoms 23 and is significantly larger than the measured moments originating from the broken bonds associated with the surface or atomic vacancies (typically in the order of less than 10 −3 emu/g) in pure ZnO measured using nanoparticles 24,25 or nanograined thin films. 26 However, it is quite comparable to the calculated M S of 0.069−0.34 emu/g obtained based on our first principles calculation discussed earlier, assuming the magnetic moment of 0.001−0.005 μ B /atom depending on the thickness of the nanoplates as in Table 1. Alternatively, it was reported by Yi et al 27 that the presence of very small Zn clusters embedded in ZnO matrix may lead to the measurable magnetic moment in ZnO.…”

Magnetic field cycling effect on the non-linear current-voltage characteristics and magnetic field induced negative differential resistance in α-Fe1.64Ga0.36O3 oxide

“…6 We could detect an extra phase whose total contribution is less than 2% of the rhombohedral and the contribution from such extremely minor phase, if really non-negligible, can be included in the contribution from grain boundary disorder and free surface, whose effect surface has been discussed for various alloyed compounds. 34,35 In fact many reports highlighted the role of surface defects at the interfaces of metal electrodes and magnetic semiconductor for the NDR effect, e.g., in Pt/TiO 2 /Pt device. 26 In such interfaces, oxygen vacancy and Schottky barrier determine the trapping and de-trapping of charge carriers, and space charge limited current (SCLC) mechanism controls I-V characteristics.…”

Defect-induced magnetism in SiC: Interplay between ferromagnetism and paramagnetism

“…Therefore, the magnetic moments can not be increased by increasing the fluence of irradiation all the time, while, the amount of paramagnetic centers can be scaled up with neutron fluence and show saturation at very large fluences. The locally accumulation of ferromagnetic defects has also been suggested for defective ferromagnetic oxides [14,19,79].…”

“…A fundamental question is whether materials containing only s or p electrons can be ferromagnetic. For nearly two decades, there have been various theoretical and experimental studies devoted to clarifying this question [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. It turns out that materials with completely filled 3d or 4f shells or with only s or p electrons can be ferromagnetic when they contain defects.…”