Ab-initio approach to the stability and the structural, electronic and magnetic properties of the (001) Znfe2O4 surface terminations

Abstract

We present a Density Functional Theory (DFT) based study of the structural and magnetic properties of the (001) surface of the semiconducting oxide ZnFe 2 O 4 (spinel structure). The calculations were performed using the DFT based ab initio plane wave and pseudopotential method as implemented in the Quantum Espresso code. The all electron Full-potential linearized-augmented-plane-wave method (FP-LAPW) was also employed to check the reproducibility of the plane wave method. In both calculations the DFT+U methodology was employed and different (001) surface terminations of ZnFe 2 O 4 were studied. We find that the surface terminated in Zn is the stable one. For all the (001) surface terminations our calculations predict that the Zn-Fe cationic inversion (antisites), which are defects in bulk ZnFe 2 O 4 , becomes stable and an integral part of the surface. Also, a ferrimagnetic behavior is predicted for the case of anti-sites in the superficial layer. Our results for different properties of the surface of ZnFe 2 O 4 are compared with those obtained in bulk samples and those reported in the literature.

Theoretical Study of Polar Spinel Surfaces: Effect of Termination and Cation Inversion on Structure and Stability

“…Symmetric, nonstoichiometric surface models were used to study different terminations of the ZnFe 2 O 4 (100) surface. 40 None of these surface models is comparable to those used in this work. In our previous work, 7 we employed the same defective surface model of the Zn-terminated (100) surface but did not compare the stability of different surface terminations.…”

“…With and without BSSE correction, the surface stability order is (100) Zn < (111) Fe(Zn) < (100) Fe < (110) Fe < (110) mix. The Zn-terminated (100) surface without antisites has also been found to be most stable by Rodrigues et al 40 The Fe-terminated (100) surface undergoes a different relaxation from the corresponding MgAl 2 O 4 surface. Half of the topmost octahedral oxygen atoms move in the y-direction assuming a pseudotetrahedral position in between the topmost Fe and Zn atoms.…”

“…Small energy differences were also found for antisite defects in symmetric models of the (100) surface of ZnFe 2 O 4 which tie in well with our results. 40 Despite the lower surface energy, the inverse FM surface models are less stable than the Wulff Construction of Single-Crystal Shapes. In order to predict the shapes of single crystals of MgAl 2 O 4 and ZnFe 2 O 4 , we applied the Wulff construction scheme 63 using the open-source program VESTA.…”

“…The effect of spin state and cation distribution on electronic properties of the ZnFe 2 O 4 bulk has previously been studied at different levels of theory. − Adding to our work on the bulk, we have also considered the effect of cation inversion on the band positions of the (100) surface of ZnFe 2 O 4 . While the low-index surfaces of MgAl 2 O 4 have been studied extensively, only a few theoretical studies of ZnFe 2 O 4 surfaces are available. ,− We present a comprehensive and comparative study on the structure and stability of low-index MgAl 2 O 4 and ZnFe 2 O 4 surfaces at the hybrid density functional theory (DFT) level, taking into account cation inversion and possible spin states.…”

Fabrication of Mn1Zn Fe2O4 ferrofluids from natural sand for magnetic sensors and radar absorbing materials

“…ZnFe 2 O 4 nanoparticles show ferrimagnetic behavior at room temperature and antiferromagnetic ordering below 9 K [ 38 ]. Other showed that the ZnFe 2 O 4 nanoparticles have ferrimagnetic behavior at room temperature [ 39 , 40 ]. Interestingly, the ZnFe 2 O 4 ferrofluid sample has a fractal dimension of D ~1, which is interpreted as a chain arrangement resembling a rod.…”