Oxygen vacancy enhanced room temperature magnetism in Al-doped MgO nanoparticles (original) (raw)
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International Journal of Engineering, 2020
Pure and doped magnesium oxide nanoparticles were successfully synthesized employing a sol-gel process. The synthesized nanoparticles were characterized by thermal differential analysis, X-ray powder diffraction, transmission electron microscopy, scanning electron microscope, energy-dispersive X-ray spectroscopy, and vibrating sample magnetometer. X-ray diffraction patterns confirmed the crystallization of MgO structure and correspondingly ratified that the transition metal atoms were incorporated into the MgO host lattice. The crystallite size decreases as the concentration of dopants were augmented. TEM images showed that the particles of pristine magnesium oxide were embedded in the sheet matrix of the graphene-like layer with a size of 22.06 nm. The EDS spectra revealed the presence of carbon in pure MgO nanoparticles, while nickel and chromium were distributed in the host lattice. Based on VSM measurements, room temperature ferromagnetism in pristine MgO-NPs could be ascribed to the presence of either Mg vacancy or carbon atoms. Furthermore, paramagnetic ordering had been observed upon doping. Overall, the prepared MgO-NPs may be found as a potential application in spintronics devices.
Ferromagnetism in Nitrogen Doped Magnesium Oxide: a First Principle Study
2011
The formation of magnetic moment in the p-orbital doped semiconductors is named d 0 magnetism, where the ion without partially filled d states is found to be responsible for the magnetism. To study origin of magnetism in such p-orbital doped semiconductors, we report a theoretical investigation of electronic and magnetic properties of N doped MgO, with and without an oxygen vacancy. The first principle calculations have been performed using ab initio total energy calculations with in generalized gradient approximation (GGA) as embodied in projector augmented wave (PAW) method. Our results suggest that without other defects, the oxygen vacancy does not reflect magnetism. It is observed that when N, substitutes for oxygen, it shows spontaneous magnetization and affect the magnetic moment of dopant. Although, the total magnetic moment of the system is independent of the presence of oxygen vacancies and found to be 1 B.
Possible ferromagnetism in MgO
Solid State Communications, 2009
We study the impact of vacancies on the magnetism of MgO and TiO 2 nanoparticles, and develop fist-principle calculations to ascertain the origin of the induced polarization. Theoretically, we expect ferromagnetism only for the case of MgO with cation defects. Experimentally, we observed a small magnetic signal probably due to imperfections in the lattice order, perhaps at the nanoparticles surface.
Scientific Reports
We investigated the effects of both intrinsic defects and hydrogen atom impurities on the magnetic properties of MgO samples. MgO in its pure defect-free state is known to be a nonmagnetic semiconductor. We employed density-functional theory and the Heyd–Scuseria–Ernzerhof (HSE) density functional. The calculated formation energy and total magnetic moment indicated that uncharged {\mathrm{V}}_{\mathrm{Mg}}^{0}VMg0andsinglychargedV Mg 0 and singly chargedVMg0andsinglycharged{\mathrm{V}}_{\mathrm{Mg}}^{-1}$$ V Mg - 1 magnesium vacancies are more stable than oxygen vacancies (VO) under O-rich growth conditions and introduce a magnetic moment to MgO. The calculated density of states (DOS) results demonstrated that magnetic moments of VMg result from spin polarization of an unpaired electron of the partially occupied valence band, which is dominated by O 2p orbitals. Based on our calculations, VMg is the origin of magnetism and ferromagnetism in MgO. In contrast, the magnetic moment of the magnetic VMg-MgO crystal is s...
Crafting ferromagnetism in Mn-doped MgO surfaces with p-type defects
Science and Technology of Advanced Materials, 2014
We have employed first-principles calculations based on density functional theory (DFT) to investigate the underlying physics of unusual magnetism in Mn-doped MgO surface. We have studied two distinct scenarios. In the first one, two Mn atoms are substitutionally added to the surface, occupying the Mg sites. Both are stabilized in the Mn + 3 valence state carrying a local moment of 4.3 μ B having a high-spin configuration. The magnetic interaction between the local moments display a very short-ranged characteristic, decaying very quickly with distance, and having antiferromagnetic ordering lower in energy. The energetics analysis also indicates that the Mn ions prefer to stay close to each other with an oxygen atom bridging the local interaction. In the second scenario, we started exploring the effect of native defects on the magnetism by crafting both Mg and O vacancies, which are p-and n-type defects, respectively. It is found that the electrons and holes affect the magnetic interaction between Mn ions in a totally different manner. The n-type defect leads to very similar magnetism, with the AFM configuration being energetically preferred. However, in the presence of Mg vacancy, the situation is quite different. The Mn atoms are further oxidized, giving rise to mixed Mn(d) ionic states. As a consequence, the Mn atoms couple ferromagnetically, when placed in the close configuration, and the obtained electronic structure is coherent with the double-exchange type of magnetic interaction. To guarantee the robustness of our results, we have benchmarked our calculations with three distinct theory levels, namely DFT-GGA, DFT-GGA+U and DFT-hybrid functionals. On the surface, the Mg vacancy displays lower formation energy occurring at higher concentrations. Therefore, our model systems can be the basis to explain a number of controversial results regarding transition metal doped oxides.
We have employed first-principles calculations based on density functional theory (DFT) to investigate the underlying physics of unusual magnetism in Mn-doped MgO surface. We have studied two distinct scenarios. In the first one, two Mn atoms are substitutionally added to the surface, occupying the Mg sites. Both are stabilized in the Mn + 3 valence state carrying a local moment of 4.3 μ B having a high-spin configuration. The magnetic interaction between the local moments display a very short-ranged characteristic, decaying very quickly with distance, and having antiferromagnetic ordering lower in energy. The energetics analysis also indicates that the Mn ions prefer to stay close to each other with an oxygen atom bridging the local interaction. In the second scenario, we started exploring the effect of native defects on the magnetism by crafting both Mg and O vacancies, which are p-and n-type defects, respectively. It is found that the electrons and holes affect the magnetic interaction between Mn ions in a totally different manner. The n-type defect leads to very similar magnetism, with the AFM configuration being energetically preferred. However, in the presence of Mg vacancy, the situation is quite different. The Mn atoms are further oxidized, giving rise to mixed Mn(d) ionic states. As a consequence, the Mn atoms couple ferromagnetically, when placed in the close configuration, and the obtained electronic structure is coherent with the double-exchange type of magnetic interaction. To guarantee the robustness of our results, we have benchmarked our calculations with three distinct theory levels, namely DFT-GGA, DFT-GGA+U and DFT-hybrid functionals. On the surface, the Mg vacancy displays lower formation energy occurring at higher concentrations. Therefore, our model systems can be the basis to explain a number of controversial results regarding transition metal doped oxides.
d° Ferromagnetism of Magnesium Oxide
Condensed Matter
Magnetism without d-orbital electrons seems to be unrealistic; however, recent observations of magnetism in non-magnetic oxides, such as ZnO, HfO2, and MgO, have opened new avenues in the field of magnetism. Magnetism exhibited by these oxides is known as d° ferromagnetism, as these oxides either have completely filled or unfilled d-/f-orbitals. This magnetism is believed to occur due to polarization induced by p-orbitals. Magnetic polarization in these oxides arises due to vacancies, the excitation of trapped spin in the triplet state. The presence of vacancies at the surface and subsurface also affects the magnetic behavior of these oxides. In the present review, origins of magnetism in magnesium oxide are discussed to obtain understanding of d° ferromagnetism.
2011
The formation of magnetic moment due to the dopants with p-orbital (d-orbital) is named d 0 (d−) magnetism, where the ion without (with) partially filled d states is found to be responsible for the observed magnetic properties. To study the origin of magnetism at a fundamental electronic level in such materials, as a representative case, we theoretically investigate ferromagnetism in MgO doped with transition metal (Mn) and non-metal (C). The generalized gradient approximation based first-principles calculations are used to investigate substitutional doping of metal (Mn) and nonmetal (C), both with and without the presence of neighboring oxygen vacancy sites. Furthermore, the case of co-doping of (Mn, C) in MgO system is also investigated. It is observed that the oxygen vacancies do not play a role in tuning the ferromagnetism in presence of Mn dopants, but have a significant influence on total magnetism of the C doped system. In fact, we find that in MgO the d 0 magnetism through C doping is curtailed by pairing of the substitutional dopant with naturally occurring O vacancies. On the other hand, in case of (Mn, C) co-doped MgO the strong hybridization between the C (2 p) and the Mn(3d) states suggests that co-doping is a promising approach to enhance the ferromagnetic coupling between the nearestneighboring dopant and host atoms. Therefore, (Mn,C) co-doped MgO is expected to be a ferromagnetic semiconductor with long ranged ferromagnetism and high Curie temperature.
Ferromagnetism and diamagnetism behaviors of MgO synthesized via thermal decomposition method
Journal of Alloys and Compounds, 2017
MgO powders were synthesized by a thermal decomposition method which was determined by differential scanning calorimetry coupled with thermogravimetric analysis (TG/DSC). The starting material, Mg(OH) 2, was calcined at 400°C, 450°C and 500°C for 1 hour each to obtain the MgO powders. Phase composition, morphology and magnetic properties at room temperature of calcined powders were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fourier transform infrared Spectroscopy (FTIR) and vibrating sample magnetometer (VSM), respectively. Both Mg(OH) 2 and MgO phases were found in all calcined powders. The combination of ferromagnetism and diamagnetism at room temperature of all powders were observed. It is believed to be attributed to Mg vacancies and defect in the MgO and Mg(OH) 2 structures.
Undoped and cobalt doped MgO nanoparticles (Mg 1-x Co x O, x = 0, 0.03, 0.06 and 0.12) were prepared by co-precipitation method. The synthesized samples were characterized by using X-ray diffraction (XRD), differential thermal analysis (DTA) and Ultraviolet-Visible (UV-Vis) spectroscopy. The UV-Visible absorption spectra showed a redshift with the increase in cobalt doping content in MgO host lattice while corresponding bandgap energy of cobalt doped MgO-NPs was decreased with the increase of doping concentration. The XRD patterns revealed the formation of rock salt MgO phase nanostructures. The Rietveld analysis revealed the formation of impurity phase (Co 3 O 4 ), which was remarkably appear at higher doping concentration (x = 0.12). Rietveld refinement was utilized to investigate the individual influences of coherent domain sizes and lattice strain on the peak broadening of the pure and cobalt doped MgO-NPs. The coherent domain size increased from 7.44 nm to 8.11 nm with increasing Co doping amount up to x = 0.06. The strain decreased with increasing in cobalt content. The decreasing trend in lattice constant "a" was observed with increasing doping concentration which confirms the incorporation of Co ions into the MgO host lattice. Furthermore, the linear and planar defects were also considered. First-principles calculations based on DFT were employed to determine elastic constants for the pure and doped MgO. These values were then used in combination with X-ray diffraction data to measure stacking fault energies as a function of doping concentration. The results showed that the stacking fault energy decreased as the doping concentration increase. The formation enthalpy and bonding properties of the studied compounds were also inspected. Further, the magnetic features of Co monodoping and (Co, Mg or O vacancy) co-doping in MgO host lattice were studied. The results reveal that the studied compounds may have potential applications in spintronics and magnetic data storage.