Influence of diamagnetic impurity on mid‐IR absorption in antiferromagnetic insulator NiO

Abstract

The influence of diamagnetic magnesium impurities on the absorption band at ~2000 cm -1 was studied in polycrystalline Ni c Mg 1-c O solid solutions with c=0. 99, 0.98, 0.97, 0.95, 0.90, 0.80, 0.70 and 0.60. The composition and temperature dependences of the absorption suggest that the band has magnetic origin related to simultaneous excitation of two-magnons at the Brillouin-zone boundary and one phonon. . The absorption spectrum of NiO in mid-infrared spectral range has a band at ~2000 cm -1 (0.24 eV), observed previously in [5][6][7][8][9][10]. This band was attributed to an impurity induced absorption in [5]. However, further studies have shown its connection with magnetic ordering in . It was found that upon temperature increase, the band becomes less intensive and its position shifts to lower energies, till the band disappears completely above the Nèel temperature [6,7,10]. The energy position of the band was attributed to the joint excitation of two magnons and one phonon [8,9]. The theoretical description of such transitions was given in [10,11] and more recently in [12].The magnetic properties of nickel oxide can be strongly influenced by admixture of non-magnetic ions [13]. For example, Ni c Mg 1-c O solid solutions represent a nice example of diluted antiferromagnetic system. Its magnetic properties vary from antiferromagnetic-like behaviour for c=1, to diamagnetic-like behaviour for c=0 [14,15]. For intermediate compositions with c>0.3, paramagnetic-toantiferromagnetic phase transition occurs upon cooling [14,15].In this work, we have studied the influence of diamagnetic magnesium impurities on the absorption band at ~2000 cm -1 in polycrystalline Ni c Mg 1-c O solid solutions. Polycrystalline solid solutions Ni c Mg 1-c O (c=0.99, 0.98, 0.97, 0.95, 0.90, 0.80, 0.70 and 0.60) were prepared using ceramic technology from the appropriate amounts of aqueous solutions of Mg(NO 3 ) 2 ·6H 2 O and Ni(NO 3 ) 2 ·6H 2 O salts, which were mixed and slowly evaporated. The remaining dry 'flakes' were heated up to 500-600 ºC to remove NO 2 completely. The obtained polycrystalline solid solutions were pressed and annealed during 100 hours at 1200 ºC in air and then rapidly cooled down to room temperature. The pure polycrystalline NiO and MgO were obtained using the same method by thermal decomposition of the above mentioned salts. These Ni c Mg 1-c O solid solutions have greenish

Hybrid density functional theory description of N- and C-doping of NiO

“…This AFM ordering for NiO is well known [43].The HSE06 local magnetic moment on the Ni ion is 1.65 µ B which is consistent with the experimental value of 1.64 µ B [41] and the previous DFT+U result of 1.68 µ B [27].…”

“…The band gap calculated from HSE06 is 4.2 eV, comparing reasonably with the experimental band gap in the range 3.8 -4 eV [42,43], showing a small overestimation with HSE06, and comparing more favourably than the strongly underestimated DFT+U band gap, which is 2.6 eV [27]. HSE06 can overestimate band gaps of metal oxides, e.g.…”

Synchrotron-based far-infrared spectroscopy of nickel tungstate

“…Therefore, they are intensively used nowadays in infrared (IR) spectroscopy to probe vibrational properties of single crystalline [1,2], microcrystaline [2,3] and nanocrystalline materials [4][5][6][7]. Besides that infrared spectrum can contain information on magnetic excitations, which were observed, for example, in antiferromagnetic metal oxides as CoO, NiO and solid solutions Ni c Mg 1-c O and Co c Mg 1-c O [2,8].…”

Spin–phonon interaction effects in pure and ion‐doped NiO nanoparticles

“…The Raman scattering by phonons and magnons in AFM NiO was studied by many authors [3][4][5][6]. Raman frequencies of both optical and acoustical phonons are shifted in the spectra obtained from pure [7,8] and Mg-doped NiO [9,10], from FeO [11,12], a-Fe 2 O 3 [13], Mn 3 O 4 [14] nanostructures compared to their positions in the spectra from the bulk material. The origin of these phonon frequency shift is still under debate.…”

“…Another one is related to the phonon localization by defects. The Raman modes of AFM NPs are very sensitive to doping with different ions [9,10]. Electron-phonon and spin-phonon interactions play an important role in the lattice dynamic of AFM NPs.…”