Article Cite This: ACS Appl. Electron. Mater. XXXX, XXX, XXX−XXX
pubs.acs.org/acsaelm
Modification of Electrical and Magnetic Properties of Fe3O4 Epitaxial Thin Films by Nitrogen Substitution for Oxygen Satoshi Fujiwara,† Yuji Kurauchi,† Yasushi Hirose,*,† Isao Harayama,§,∥ Daiichiro Sekiba,§,∥ and Tetsuya Hasegawa†,‡ †
Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan Kanagawa Academy of Science and Technology, 3-2-1 Sakado, Takatsu-ku, Kawasaki 213-0012, Japan § Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan ∥ Tandem Accelerator Complex, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan ACS Appl. Electron. Mater. Downloaded from pubs.acs.org by OCCIDENTAL COLG on 04/15/19. For personal use only.
‡
S Supporting Information *
ABSTRACT: Epitaxial thin films of nitrogen-substituted Fe3O4 (Fe3O4−yNy) were synthesized on MgO (001) substrates by using nitrogen-plasma-assisted pulsed laser deposition. The obtained Fe3O4−yNy thin films showed ferrimagnetic behavior at room temperature. The carrier density of the films was decreased by nitrogen substitution up to y = 0.4. These properties were similar to those of A-site (tetrahedral site)-substituted Fe 3O4, such as ZnxFe3−xO4 or MnxFe3−xO4, previously reported. On the other hand, the electrical resistivity of the Fe3O4−yNy thin films at room temperature was rather insensitive to y, in sharp contrast to ZnxFe3−xO4 or MnxFe3−xO4, of which the resistivity drastically increased with increase of x. These results indicated that nitrogen substitution is an effective method to control the carrier density of Fe3O4 without disturbing the carrier conduction through the B-site (octahedral site) Fe ion network. Density functional theory-based first-principles calculation predicted that Fe3O4−yNy is half-metallic. KEYWORDS: magnetite, spintronics, thin film, oxynitride, epitaxial growth, half metal, first-principles calculation
1. INTRODUCTION Magnetite (Fe3O4) is one of the promising materials for spintronics-based applications such as magnetic tunnel junctions and spin injection electrodes because of its ferrimagnetism with high Néel temperature (TN ≈ 860 K) and half-metallicity.1−5 Thus far, control of the physical properties of Fe3O4, especially in thin film form, has been extensively studied for device applications. The intriguing properties of Fe3O4 originate from its inverse spinel structure with two Fe sites (i.e., tetrahedral A site and octahedral B site). The Fe ions occupying A site (FeA) are present as Fe3+ (3d5), whereas the Fe ions occupying B site (FeB) are in the mixedvalence state of Fe3+ and Fe2+ (3d6), where the t2g electrons work as spin-polarized carriers through hopping between the FeB site. An established way to control the valence state of FeB is substitution of aliovalent cations for FeA. For example, Zn2+ or Mn2+ substitution for trivalent FeA reduces the number of carriers on FeB and thus increases the electrical resistivity of Fe3O4 in a controlled manner.6,7 However, unintentional substitution of FeB, not FeA, often occurs, exerting an undesirable influence on the physical properties.8 Anion substitution is an alternative approach to overcome this problem, because the spinel structure has only one oxygen site (Figure 1). For example, N3− substitution for O2− is expected to dope holes into FeB, similar to divalent cation substitution © XXXX American Chemical Society
Figure 1. FeA-site substitution and O-site substitution of Fe3O4. A dotted arrow represents unintentional substitution of FeB. Crystal structure was drawn by VESTA.10
for FeA. However, electrical and magnetic properties of nitrogen-substituted magnetite (Fe3O4−yNy) have scarcely been reported so far9 because of the lack of an established synthetic route. In this study, we fabricated spinel-type Fe3O4−yNy epitaxial thin films (y = 0−0.4) and examined their magnetic and electrical properties. We also performed first-principles calculation to investigate the effect of nitrogen Received: January 28, 2019 Accepted: April 5, 2019 Published: April 5, 2019 A
DOI: 10.1021/acsaelm.9b00051 ACS Appl. Electron. Mater. XXXX, XXX, XXX−XXX
Article
ACS Applied Electronic Materials substitution on the electronic structure and half-metallicity of Fe3O4.
2. EXPERIMENTAL SECTION Fe3O4−xNy thin films were fabricated on MgO (001) single-crystalline substrates by nitrogen-plasma-assisted pulsed laser deposition (NPAPLD).11−14 An Fe2O3 pellet (99.9% purity) sintered at 950 °C for 24 h in air was ablated by a KrF excimer laser. The substrate was heated at 300 °C by an infrared lamp heater. Films were deposited under base pressure ( 0 films. The supplied N2 gas was activated into radicals by a radiofrequency wave plasma source (SVT Associates, Model 4.5 in.). The nitrogen content of each film was controlled by adjusting the film deposition rate as a function of the pulse repetition rate of the excimer laser (2.5−20 Hz)11,15 where the input power of the plasma source was kept constant at 200W. The deposition rate was determined from the deposition time, and the film thickness was evaluated by using a stylus profiler (Veeco, Dektak 6M). The thicknesses of the films were ∼35−45 nm. The crystal structure of the films was determined by an X-ray fouraxis diffractometer (Bruker AXS, d8 discover) using Cu Kα radiation. Chemical compositions of the films were evaluated by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM−EDX) (JEOL, JSM-7100F with JED-2300). The SEM− EDX data were calibrated by standard samples of amorphous Fe3O4−xNy thin films deposited on Si substrate, of which chemical compositions were determined by elastic recoil detection analysis with a ΔE−E telescope detector for N and O as well as Rutherford backscattering spectrometry for Fe with a 38.4 MeV 35Cl beam generated by a 5 MV tandem accelerator (Micro Analysis Laboratory, The University of Tokyo [MALT]).16 The anion compositions x and y included 5% of experimental errors mainly because of statistical errors in ERDA measurements of the standard samples. Electrical resistivity and Hall resistivity were measured by using a physical property measurement system (Quantum Design, Model 6000) with the standard Hall bar geometry using a six-probe method. Magnetic properties were investigated by using a superconducting quantum interference device magnetometer (Quantum Design, MPMS-XL), where the magnetic field was applied parallel to the film surfaces. The electronic structure of Fe3O4−yNy was calculated based on the density functional theory (DFT) implemented in the Vienna Ab initio Simulation Package (VASP).17 The spin-polarized generalized gradient approximation by Perdew, Burke, and Ernzerhof (GGAPBE)18 was adopted for exchange-correlation functionals, and the GGA+U correction19 was employed to treat with the effect of Coulomb repulsion presented in the localized 3d electrons on Fe atoms. We used U = 4.0 eV after the previous theoretical report of the zinc-doped magnetite.20 A plane-wave basis set with a cutoff energy of 800 eV was used for the valence states including 3s23p63d64s2 of Fe, 2s22p4 of O, and 2s22p5 of N. The other core electrons were taken into account by the projector augmented wave method.4,21 The Brillouin zone integration was carried out by the Monkhorst−Pack scheme22 with a Γ-centered 4 × 4 × 4 k-point mesh. Calculation was performed for two model cells containing Fe6O8 (y = 0) and Fe6O7N (y = 0.5) in the trigonal primitive cell of the spinel structure. The cell parameter and atom positions were optimized until the Hellmann− Feynman force on each atom reached to less than 0.01 eV Å−1, and the pressure on the cell became less than 0.01 GPa.
Figure 2. (a) Nitrogen content y of Fe3O4−xNy thin films as a function of deposition rate. Red diamonds and blue triangles indicate samples fabricated with the shutter open and closed, respectively. (b) Detailed chemical composition of the films as a function of N/(O + N).
a function of the deposition rate, where the input power of the plasma source was fixed at 200 W. As the deposition rate increased, y monotonically decreased. Further decrease of y was achieved by blocking and deactivating the radicals with a shutter plate put between the sample and the nitrogen-plasma source. By adjusting these two parameters, y of the Fe3O4−xNy thin films was controlled within the range of y = 0−0.8. Meanwhile, the oxygen content 4 − x systematically decreased with increasing y. As a result, the total anion amount 4 − x + y was almost constant at ∼4.0 (i.e., x ≈ y in all films (Figure 2(b))), indicating substitution of N for O. Therefore, we hereafter refer to these films as Fe3O4−yNy. Epitaxial growth of the Fe3O4−yNy thin films was confirmed by X-ray diffraction (XRD) measurements. Figure 3(a,b) depicts 2θ/ω XRD patterns of the Fe3O4−yNy thin films, clearly indicating the 008 diffraction peaks of the spinel Fe3O4−yNy near the MgO 004 peak without any peaks from impurity phases. We also observed the 113 diffraction peak, which is characteristic of the spinel structure, in an asymmetric 2θ/ω scan. Figure 3(d) plots the out-of-plane lattice constant c and in-plane lattice constant a of Fe3O4−yNy as a function of y, which were calculated from the −408 peak of the reciprocal space maps (RSM) (Figure 3(c)). In all films, a was almost locked to twice of that of the MgO substrate. On the other hand, c increased with increasing y, reflecting the substitution of N3− for O2−. Notably, the slope dc/dy became steep for y = 0.6 and 0.8. This suggests that a certain number of defects, such as anion vacancy and excess octahedral Fe ions, were introduced in these two films,9 although off-stoichiometry was not detected in chemical composition analysis (Figure 2(b)) possibly because of relatively large experimental error of Δx ≈ 0.2 for the oxygen content. Hereafter, we will discuss the physical properties of the Fe3O4−yNy thin films with y = 0−0.4. The physical properties of the films with y = 0.6 and 0.8 are provided as Supporting Information. 3.2. Magnetic and Electrical Properties of Fe3O4−yNy Thin Films. First, we investigated the influence of nitrogen substitution on the magnetic property of Fe3O4. Figure 4(a) shows magnetic field dependence of the in-plane magnetization M at 300 K, where the diamagnetic contribution of the MgO substrate was subtracted. The Fe3O4−yNy thin films showed ferrimagnetic hysteresis loops at 300 K. The y = 0 (Fe3O4) film showed saturation magnetization of Ms = 2.9 μB/ f.u., which was smaller than the ideal value reported for bulk
3. RESULTS AND DISCUSSION 3.1. Epitaxial Growth of Fe3O4−yNy Thin Films. First, we examined the influence of growth parameters on the nitrogen content in the film. We found that the nitrogen content y in an Fe3O4−xNy thin film was almost independent of the input power of the plasma source in the range of 100−300 W. On the other hand, it was sensitive to the thin film deposition rate (i.e., the supply rate of Fe and O from the target).11,15 Figure 2(a) plots the nitrogen content y in the Fe3O4−xNy thin films as B
DOI: 10.1021/acsaelm.9b00051 ACS Appl. Electron. Mater. XXXX, XXX, XXX−XXX
Article
ACS Applied Electronic Materials
Figure 4. (a) In-plane magnetization vs magnetic field curves at room temperature (300 K). The inset plot shows saturation magnetization Ms at 300 K as a function of y. (b) Hall resistivity ρxy at 300 K. The inset plot shows carrier density ne as a function of y calculated from the slope under high magnetic field (orange solid lines in the main panel).
Figure 3. (a,b) 2θ/ω XRD patterns of Fe3O4−yNy thin films. (a) Wide range and (b) enlarged view around the film 008 peak. Black triangles indicate the 008 peak from the Fe3O4−yNy film. (c) Reciprocal space map around −408 peak of y = 0.3 film. (d) Out-of-plane lattice constant c and in-plane lattice constant a calculated from reciprocal space maps around −408 peaks. The dashed line indicates twice of the lattice constant of the MgO substrate.
reflecting that the carrier electrons were mainly provided by the FeB site. Notably, the carrier density ne evaluated from the slope tended to decrease with increasing y from 0 to 0.4 (Figure 4(b), inset), demonstrating that the valence state of FeB could be controlled by N3− substitution for O2−. Figure 5(a) shows the temperature dependence of resistivity ρ. A steep increase of ρ at ∼120 K, being a distinct signature of the Verwey transition, was observed in Fe3O4, whereas the transition was suppressed for Fe3O4−yNy (y > 0). Because the
Fe3O4 (4 μB/f.u.). This is probably because of the existence of antiphase boundaries in the film, as reported in the previous studies on Fe3O4 thin films.1,2,6,7,23,24 The ferrimagnetism of Fe3O4 is dominated by the antiferromagnetic superexchange interaction between FeA and FeB ions and ferromagnetic double-exchange interaction between FeB ions. Considering nominal charge balance, N3− substitution for O2− increases the amount of Fe3+ in FeB and thus enhances Ms. Experimentally, however, Ms decreased with increasing y (Figure 4(a), inset). This discrepancy may be attributable to the increase of antiphase boundaries with nitrogen introduction. We also speculate that magnetic interaction between Fe ions was weakened through formation of Fe−N−Fe bonds. Indeed, reduction of magnetic interaction by nitrogen substitution was recently reported in an antiferromagnetic iron oxynitride, Sr2FeWO6−xNx, of which TN monotonically decreased with increasing the nitrogen content x.25 Although exact evaluation of TN of the Fe3O4−yNy thin films is difficult due to intermixing between the film and the MgO substrate (Supporting Figure S1), magnetization measurements of the Fe3O4−yNy thin films (y = 0 and 0.2) below 300 K supported the reduction of TN by nitrogen substitution (Supporting Figure S2). Next, we discuss the electrical transport properties of the Fe3O4−yNy films. Figure 4(b) plots Hall resistivity ρxy of the Fe3O4−yNy thin films against magnetic field H at 300 K, clearly indicating an anomalous Hall effect originating from the ferrimagnetism. The slope of ρxy in the high magnetic field region was negative in all samples as reported for Fe3O4,7,26
Figure 5. (a) ρ−T curves of the Fe3O4−yNy thin films. (b) Resistivity at 300 K (ρ300K) of the Fe3O4−xNy thin films as a function of substitution amount y (red diamond). The black circles and blue triangles indicate ρ300K of ZnxFe3−xO4 (ZFO) and MnxFe3−xO4 (MFO) thin films, respectively.6,7 Reproduced with permission from references 6 and 7. Copyright 2005 AIP Publishing and 2009 American Physical Society. C
DOI: 10.1021/acsaelm.9b00051 ACS Appl. Electron. Mater. XXXX, XXX, XXX−XXX
Article
ACS Applied Electronic Materials
maintained in Fe3 O3.5N 0.5, which is advantageous for spintronics applications. We also performed DFT calculations under tensile strain from the MgO substrate as observed in the experiment. The DOS profiles of the strained Fe3O4 and Fe3O3.5N0.5 are almost the same as those obtained by the strain-free calculations (Supporting Figure S4), indicating that the epitaxial strain did not have a significant effect on the electronic conduction of Fe3O4−yNy.
Verwey transition of Fe3O4 is caused by the charge ordering of FeB3+ and FeB2+ accompanied by orbital order of FeB2+ with formation of three Fe-site units,27 disappearance of the transition in Fe3O4−xNy can be explained by the deviation of the FeB3+/FeB2+ ratio from unity associated with nitrogen substitution. Indeed, similar suppression of the Verwey transition has also been reported in cation-substituted MxFe3−xO4 (M = Zn, Mn).6,7 Interestingly, ρ of Fe3O4−xNy at 300 K (ρ300K) was insensitive to y (Figure 5(b)), in stark contrast to the cationsubstituted MxFe3−xO4 (M = Zn, Mn), where resistivity monotonically increased with increasing x.6,7 It is unlikely that the different behaviors of ρ300K between cation- and anionsubstituted Fe3O4 are due to a chemical pressure effect (i.e., difference in distance between FeB sites), because an increase of ρ was observed in both Zn- and Mn-substituted Fe3O4, of which the lattice parameter decreased and increased, respectively, by the substitution.6,7 Instead, we speculate that the connectivity state of the FeB network dominates the resistivity. In the case of the cation substitution, unintentional substitution for FeB site would directly disturb the carrier conduction pathway made of FeB ions, resulting in the increase in electrical resistivity. On the other hand, nitrogen substitution for the oxygen site could have little effect on the conduction path of the FeB ion network in Fe3O4. Considering the fact that the ne of Fe3O4−xNy decreased with increasing y (Figure 4(b), inset), nitrogen substitution could even enhance the carrier mobility. The above-mentioned hypothesis was supported by density functional theory (DFT) calculations of Fe3O4−yNy. Figure 6(a,b) shows the electronic density of states (DOS) calculated
4. CONCLUSION Fe3O4−xNy thin films (y = 0−0.4) were epitaxially grown on MgO (001) single-crystalline substrates by NPA-PLD. The obtained Fe3O4−xNy films showed ferrimagnetic behavior at room temperature. The density of carrier electrons was reduced by substituting nitrogen for oxygen due to oxidation of FeB. The Verwey transition characteristic of Fe3O4 was suppressed in the nitrogen-substituted films. The resistivity of Fe3O4−xNy thin films at 300 K was insensitive to y, in sharp contrast to cation-substituted Fe3O4, indicating that N substitution less disturbed the conduction path composed of FeB. Spin-polarized DFT-based calculation reveled halfmetallicity even in Fe3O3.5N0.5. These results demonstrated that N is a prospective dopant to control the carrier density of Fe3O4, maintaining the half-metallicity.
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsaelm.9b00051. X-ray diffraction pattern of an annealed sample (Supporting Figure S1), magnetization vs temperature curves (Supporting Figure S2), physical properties of the nitrogen rich samples (Supporting Figure S3), crystal and electronic structures of the strained films (Supporting Table S1 and Figure S4) (PDF)
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Yasushi Hirose: 0000-0002-0792-4631 Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes
The authors declare no competing financial interest.
■
Figure 6. Spin-polarized electronic density of states (DOS) of (a) y = 0 (Fe3O4) and (b) y = 0.5 (Fe3O3.5N0.5). The blue line in (b) corresponds to the partial DOS (PDOS) for nitrogen.
ACKNOWLEDGMENTS We thank Prof. Hiroyuki Matsuzaki of the University of Tokyo for his assistance in the ERDA measurements. This study was partially supported by the Core Research for Evolutional Science and Technology (CREST) program of the Japan Science and Technology Agency (JST) and by the Grants-inAid for Scientific Research (No. 16H06441, 16H03849, and 17H05475) from the Japan Society for the Promotion of Science (JSPS).
for y = 0 and 0.5 cells, respectively. The DOS calculated for y = 0 cell (Fe3O4) reproduced that reported previously;20,28 the DOS at the Fermi level (EF) mainly consisted of the FeB t2g band and was completely spin-polarized. Remarkably, for the y = 0.5 cell, there was no contribution to the DOS from N at the Fermi level (Figure 6(b)). This implies that the carrier conduction of Fe3O4 was less influenced by N substitution than cation substitution, even though random potential might affect the carrier mobility to some extent. Another intriguing feature seen from Figure 6 is that half-metallicity was
■
REFERENCES
(1) Margulies, D. T.; Parker, F. T.; Rudee, M. L.; Spada, F. E.; Chapman, J. N.; Aitchison, P. R.; Berkowitz, A. E. Origin of the
D
DOI: 10.1021/acsaelm.9b00051 ACS Appl. Electron. Mater. XXXX, XXX, XXX−XXX
Article
ACS Applied Electronic Materials Anomalous Magnetic Behavior in Single Crystal Fe3O4 Films. Phys. Rev. Lett. 1997, 79 (25), 5162. (2) Li, X. W.; Gupta, A.; Xiao, G.; Gong, G. Q. Transport and Magnetic Properties of Epitaxial and Polycrystalline Magnetite Thin Films. J. Appl. Phys. 1998, 83 (11), 7049−7051. (3) Seneor, P.; Fert, A.; Maurice, J. L.; Montaigne, F.; Petroff, F.; Vaurès, A. Large Magnetoresistance in Tunnel Junctions with an Iron Oxide Electrode. Appl. Phys. Lett. 1999, 74 (26), 4017−4019. (4) Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method. Phys. Rev. B: Condens. Matter Mater. Phys. 1999, 59 (3), 1758−1775. (5) Liu, H.; Di Valentin, C. Band Gap in Magnetite above Verwey Temperature Induced by Symmetry Breaking. J. Phys. Chem. C 2017, 121, 25736−25742. (6) Venkateshvaran, D.; Althammer, M.; Nielsen, A.; Geprägs, S.; Ramachandra Rao, M. S.; Goennenwein, S. T. B.; Opel, M.; Gross, R. Epitaxial ZnxFe3-XO4 Thin Films: A Spintronic Material with Tunable Electrical and Magnetic Properties. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 134405. (7) Ishikawa, M.; Tanaka, H.; Kawai, T. Preparation of Highly Conductive Mn-Doped Fe3O4thin Films with Spin Polarization at Room Temperature Using a Pulsed-Laser Deposition Technique. Appl. Phys. Lett. 2005, 86 (22), 222504. (8) Yamamoto, Y.; Tanaka, H.; Kawai, T. The Control of ClusterGlass Transition Temperature in Spinel-Type ZnFe2O4-δ Thin Film. Jpn. J. Appl. Phys. 2001, 40, L545−L547. (9) Voogt, F. C.; Smulders, P. J. M.; Wijnja, G. H.; Niesen, L.; Fujii, T.; James, M. A.; Hibma, T. NO2-Assisted Molecular-Beam Epitaxy of Wustitelike and Magnetitelike Fe Oxynitride Films on MgO(100). Phys. Rev. B: Condens. Matter Mater. Phys. 2001, 63 (12), 125409. (10) Momma, K.; Izumi, F. VESTA 3 for Three-dimensional Visualization of Crystal, Volumetric and Morphology Data. J. Appl. Crystallogr. 2011, 44 (6), 1272−1276. (11) Takahashi, J.; Hirose, Y.; Oka, D.; Nakao, S.; Yang, C.; Fukumura, T.; Harayama, I.; Sekiba, D.; Hasegawa, T. CompositionInduced Structural, Electrical, and Magnetic Phase Transitions in AXType Mixed-Valence Cobalt Oxynitride Epitaxial Thin Films. Appl. Phys. Lett. 2015, 107 (23), 231906. (12) Oka, D.; Hirose, Y.; Fukumura, T.; Hasegawa, T. Heteroepitaxial Growth of Perovskite CaTaO2N Thin Films by Nitrogen Plasma-Assisted Pulsed Laser Deposition. Cryst. Growth Des. 2014, 14 (1), 87−90. (13) Oka, D.; Hirose, Y.; Kamisaka, H.; Fukumura, T.; Sasa, K.; Ishii, S.; Matsuzaki, H.; Sato, Y.; Ikuhara, Y.; Hasegawa, T. Possible Ferroelectricity in Perovskite Oxynitride SrTaO2N Epitaxial Thin Films. Sci. Rep. 2015, 4, 4987. (14) Suzuki, A.; Hirose, Y.; Oka, D.; Nakao, S.; Fukumura, T.; Ishii, S.; Sasa, K.; Matsuzaki, H.; Hasegawa, T. High-Mobility Electron Conduction in Oxynitride: Anatase TaON. Chem. Mater. 2014, 26 (2), 976−981. (15) Sano, M.; Hirose, Y.; Nakao, S.; Hasegawa, T. Strong Carrier Localization in 3d Transition Metal Oxynitride LaVO3−xNx Epitaxial Thin Films. J. Mater. Chem. C 2017, 5, 1798−1802. (16) Harayama, I.; Nagashima, K.; Hirose, Y.; Matsuzaki, H.; Sekiba, D. Development of ΔE-E Telescope ERDA with 40 MeV 35Cl7+ Beam at MALT in the University of Tokyo Optimized for Analysis of Metal Oxynitride Thin Films. Nucl. Instrum. Methods Phys. Res., Sect. B 2016, 384, 61−67. (17) Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54 (16), 11169−11186. (18) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77 (18), 3865− 3868. (19) Dudarev, S. L.; Botton, G. A.; Savrasov, S. Y.; Humphreys, C. J.; Sutton, A. P. Electron-Energy-Loss Spectra and the Structural Stability of Nickel Oxide: An LSDA+U Study. Phys. Rev. B: Condens. Matter Mater. Phys. 1998, 57 (3), 1505−1509.
(20) Cheng, Y. H.; Li, L. Y.; Wang, W. H.; Liu, H.; Ren, S. W.; Cui, X. Y.; Zheng, R. K. Tunable Electrical and Magnetic Properties of Half-Metallic ZnxFe3-XO4 from First Principles. Phys. Chem. Chem. Phys. 2011, 13, 21243−21247. (21) Blöchl, P. E. Projector Augmented-Wave Method. Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 50 (24), 17953. (22) Monkhorst, H. J.; Pack, J. D. Special Points for Brillouin-Zone Integrations. Phys. Rev. B 1976, 13 (12), 5188−5192. (23) Margulies, D. T.; Parker, F. T.; Spada, F. E.; Goldman, R. S.; Li, J.; Sinclair, R.; Berkowitz, A. E. Anomalous Moment and Anisotropy Behavior in Fe3O4 Films. Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 53 (14), 9175−9187. (24) Bollero, A.; Ziese, M.; Höhne, R.; Semmelhack, H. C.; Köhler, U.; Setzer, A.; Esquinazi, P. Influence of Thickness on Microstructural and Magnetic Properties in Fe3O4 Thin Films Produced by PLD. J. Magn. Magn. Mater. 2005, 285, 279−289. (25) Ceravola, R.; Oró-Solé, J.; Black, A. P.; Ritter, C.; Puente Orench, I.; Mata, I.; Molins, E.; Frontera, C.; Fuertes, A. Topochemical Synthesis of Cation Ordered Double Perovskite Oxynitrides. Dalt. Trans. 2017, 46, 5128−5132. (26) Takaobushi, J.; Tanaka, H.; Kawai, T.; Ueda, S.; Kim, J. J.; Kobata, M.; Ikenaga, E.; Yabashi, M.; Kobayashi, K.; Nishino, Y.; et al. Fe3-XZnxO4 Thin Film as Tunable High Curie Temperature Ferromagnetic Semiconductor. Appl. Phys. Lett. 2006, 89 (24), 242507. (27) Senn, M. S.; Wright, J. P.; Attfield, J. P. Charge Order and Three-Site Distortions in the Verwey Structure of Magnetite. Nature 2012, 481, 173−176. (28) Zhang, Z.; Satpathy, S. Electron States, Magnetism, and the Verwey Transition in Magnetite. Phys. Rev. B: Condens. Matter Mater. Phys. 1991, 44 (24), 13319−13331.
E
DOI: 10.1021/acsaelm.9b00051 ACS Appl. Electron. Mater. XXXX, XXX, XXX−XXX
