Experimental and theoretical studies on induced ferromagnetism of new (1 − x)Na0.5Bi0.5TiO3 + xBaFeO3−δ solid solution

Abstract

New solid solution of Na0.5Bi0.5TiO3 with BaFeO3−δ materials were fabricated by sol–gel method. Analysis of X-ray diffraction patterns indicated that BaFeO3−δ materials existed as a well solid solution and resulted in distortion the structure of host Na0.5Bi0.5TiO3 materials. The randomly incorporated Fe and Ba cations in the host Na0.5Bi0.5TiO3 crystal decreased the optical band gap from 3.11 to 2.48 eV, and induced the room-temperature ferromagnetism. Our density-functional theory calculations further suggested that both Ba for Bi/Na-site and Fe dopant, regardless of the substitutional sites, in Na0.5Bi0.5TiO3 lead to the induced magnetism, which is illustrated in terms of the exchange splitting between spin subbands through the crystal field theory and Jahn–Teller distortion effects. Our work proposes a simple method for fabricating lead-free ferroelectric materials with ferromagnetism property for multifunctional applications in smart electronic devices.

Surface ferromagnetism of complex defects lead‐free ferroelectric Bi0.5Na0.5TiO3 materials

“…As we have seen, the non‐spin polarization emerges around the Fermi‐level, implying that the perfect BNT (110) surface is non‐magnetic because there is no unpaired electron. The result is consistent with theoretical and experimental studies on BNT (100) surface by Ju et al 10,11 and also agrees with bulk BNT 13,15,27 …”

“…10 The calculation for surface energy among the (010), (100), (101) and (111) surfaces indicated that the (100) surface is the most stable of the four kinds of surfaces. 11 However, the calculation for the (100) BNT surface direction was not consistent with the experimental results given in Refs [10][11][12][13][14][15], where the BNT (110) direction was favoured for crystal growth. Thus, we suggested that the observed room-temperature ferromagnetism in BNT materials could be contributed by BNT (110)-surface defects rather than that of (100)-surface defects.…”

“…For the perfect BNT (110) surface, the absorption unit is almost equal to zero in the low photon‐energy region and increases rapidly in the high photon‐energy region. These characteristics were correspondent with the bulk rhombohedral BNT 12,13,17,23,27 . Compared with the perfect surface, the absorption boundary of each BNT (110) with defects seems substantially extended toward the low photon‐energy region.…”

“…The electronic band structure and total density of state (TDOS) of the perfect BNT (110) surface in Figure 2A,B, respectively, indicate that the BNT (110) surface has dielectric properties with a bandgap of $ 2.10 eV. Meanwhile, the bulk BNT exhibits a direct bandgap of 2.86 eV via previous calculation 13,23,24 or 3.07 eV via experimental report by G. Jones. 21 These results are indeed quite typical in DFT calculations for oxide perovskites.…”

“…The interstitial defects on BNT (110) surface began with the idea that alkali and transition metals can substitute the interstitial on the structure and influence magnetism. Previous reports have also been investigated 13,14,27 . Interstitial defects are atoms that occupy a site in the structure at which there is usually not an atom.…”