Ferromagnetism in Nitrogen Doped Magnesium Oxide: a First Principle Study (original) (raw)
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Ferromagnetism in nitrogen-doped MgO: Density-functional calculations
Physical Review B, 2009
The magnetic state of Nitrogen-doped MgO, with N substituting O at concentrations between 1% and the concentrated limit, is calculated with density-functional methods. The N atoms are found to be magnetic with a moment of 1 µB per Nitrogen atom and to interact ferromagnetically via the double exchange mechanism. The long-range magnetic order is established above a finite concentration of about 1.5% when the percolation threshold is reached. The Curie temperature TC increases linearly with the concentration, and is found to be about 30 K for 10% concentration. Besides the substitution of single Nitrogen atoms, also interstitial Nitrogen atoms, clusters of Nitrogen atoms and their structural relaxation on the magnetism are discussed. Possible scenarios of engineering a higher Curie temperature are analyzed, with the conclusion that an increase of TC is dicult to achieve, requiring a particular attention to the choice of chemistry.
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.
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.
Ab Initio Study on Nitrogen or Carbon Doped Magnesium Oxide
IEEE Transactions on Magnetics, 2000
The ferromagnetism induced by nitrogen (N) or carbon (C) atoms in magnesium oxide (MgO) is studied by using ab initio calculation based on the density functional theory. The calculation shows that single N or C impurity may induce local magnetic moment to MgO due to the localization of -electrons. Moreover, the calculation of two impurities in one supercell shows that the stability of ferromagnetism in both N:MgO and C:MgO depends on the distance between the two impurities. The energy difference between the ferromagnetic and antiferromagnetic states in some situations is smaller than 28 meV, the thermal energy at room temperature, suggesting that both the localization of the -electrons and the distance between the impurities may influence the stability of ferromagnetism.
Possible d0 ferromagnetism in MgO doped with nitrogen
Physical Review B, 2009
We study the possibility of d 0 ferromagnetism in the compound MgO doped with nitrogen (N). The Haldane-Anderson impurity model is formulated within the tight-binding approximation for determining the host band-structure and the impurity-host hybridization. Using the quantum Monte Carlo technique, we observe a finite local moment for an N impurity, and long-range ferromagnetic correlations between two N impurities. The ferromagnetic correlations are strongly influenced by the impurity bound state. When the ferromagnetic correlation between a pair of impurities is mapped onto the isotropic Heisenberg model for two spin-1/2 particles, the effective exchange constant J12 is found to increase with increasing temperature. Similar temperature dependence of J12 is also obtained in other diluted magnetic semiconductors, such as zincblende ZnO doped with Mn. The temperature dependence of J12 suggests that the mapping of the full Hamiltonian onto the spin Hamiltonian cannot fully describe the magnetic correlations for the diluted magnetic semiconductors at least in the limit of low impurity spin.
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...
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.
Optik, 2017
The local spin density approximation with Hubbard-like coulomb term based on first principles calculations are used to investigate a substitute doping of transition metal Mn in MgO. Under the crystal field theory and according to the intensity of the ligand field, the d 4d 8 transition elements can have two possible configurations such as the case of Mn(d 5), in its low spin configuration that represents a strong field, the Mn +2 doped MgO material has a halfmetallic character in the two proposed studies approximations: the local spin density approximation (LSDA) and (LSDA+U), a character that will enable to change the magnetic, electronic and optical properties., This result is supported by the sp-d exchange mechanism calculation confirming that the coupling between impurity and ligand is completely ferromagnetic. The material has a magnetic moment of about 1µB, mainly due to the Mn impurity of around 95% in LSDA+U case. In optical propriety the material shows a slight spin polarization and reduction of band gap of around 5% with strong filed in LSDA+U case.
Oxygen vacancy enhanced room temperature magnetism in Al-doped MgO nanoparticles
Applied Physics Letters, 2013
We have measured the room temperature magnetization in Al-substituted magnesium oxide, Mg(Al)O nanoparticles with Al fractions of up to 5 at. %. All samples, including undoped MgO nanoparticles, exhibit weak room temperature ferromagnetism, with the saturation magnetization reaching a maximum of 0.023 emu/g at 2 at. % of Al. X-ray photoelectron spectroscopy identifies the presence of oxygen vacancies in both doped and undoped MgO nanoparticles, with the vacancy concentration increasing upon vacuum annealing of Mg(Al)O, resulting in two-fold enhancement of the saturation magnetization for 2 at. % Al-doped MgO. Our results suggest that the oxygen vacancies are largely responsible for the weak room temperature ferromagnetism in MgO.