Growth and charge ordering of epitaxial YbFe₂O₄ films on sapphire using Fe₃O₄ buffer layer

Abstract

Well-crystallized epitaxial YbFe 2 O 4 films were prepared on an α-Al 2 O 3 (001) substrate using an Fe 3 O 4 buffer layer. Fe 3 O 4 has a relatively small lattice mismatch with both YbFe 2 O 4 and α-Al 2 O 3 . Electron diffraction analysis combined with transmission electron microscopy revealed the epitaxial relationship to be α-Al 2 O 3 [110](001) k Fe 3 O 4 [ 211](111) k YbFe 2 O 4 [110](001). Moreover, superlattice spots due the Fe 2+ -Fe 3+ charge order state of YbFe 2 O 4 were clarified. The Fe 2+ /Fe 3+ ratio in YbFe 2 O 4 was nearly stoichiometric. The film exhibited a ferrimagnetic transition at >220 K and a nonlinear current-voltage characteristic at room temperature. These results confirmed the good crystallinity and stoichiometry of the obtained YbFe 2 O 4 films.

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“…Various trivalent ions are selected as R ion in reported films: Lu, [18][19][20][21][22][23][24][25] Yb, [26][27][28] Tm 17 and In. 29 The change in R ions is unlikely to affect intrinsically as well as for bulk.…”

“…29 The change in R ions is unlikely to affect intrinsically as well as for bulk. These films are fabricated on various substrates: Al 2 O 3 (001), 18,21,25,26,28 YSZ(111), 17,19,24,27 ZnO(001), 29 MgO(111), 20,22,23 MgAl2O4(111) 23 and 6H-SiC(001). 23 Also various deposition techniques are tried: pulsed laser deposition (PLD), 17,18,20,21,24,27,29 electron beam deposition (EB), 19,25,26 molecular beam epitaxy (MBE), 22,23 and rf magnetron sputtering.…”

“…23 Also various deposition techniques are tried: pulsed laser deposition (PLD), 17,18,20,21,24,27,29 electron beam deposition (EB), 19,25,26 molecular beam epitaxy (MBE), 22,23 and rf magnetron sputtering. 28 The most popular way to fabricate RFe 2 O 4 film is PLD. The ablation is performed on RFe 2+x O 4+y target prepared by solid state reaction.…”

“…23 In these various deposition techniques, much effort has been made to get high stoichiometric film. 18,21,23,27,28 The most popular way to overcome easier vaporization of Fe is deposition in Fe-rich environment: Fe enriched target or higher power of Fe source. Kashimoto R et al 27 suppressed revaporization of Fe ion by detail investigation of the emission intensity variation of each element with defocus degree, chamber pressure and substrate temperature.…”

“…However, the film fabrication of this material is still a developing research due to the difficulty in selecting substrates and keeping the stoichiometory, which changes various properties significantly. 15, 16 13 reports have been published by 2017, [17][18][19][20][21][22][23][24][25][26][27][28][29] following the first report by M. Seki et al in 2010. 17 In this paper, the film growth and electric, magnetic and optical properties of the films are briefly reviewed.…”