Structural, magnetic and optical properties of Y bFe2O4 films deposited by spin coating

Abstract

Rare-earth iron oxides (RFe2O4) have attracting attention as new electronic device materials because of their numerous functionalities, such as electronic ferroelectricity, ferrimagnetism, and high infrared absorption. In this paper, nearly monophasic Y bFe2O4 films were prepared on α-Al2O3(001) substrates by the spin coating method using an aqueous-based Y bFe2O4 solution. The solution was composed of a stoichiometric ratio of Y b(CH3COO)3 and Fe(NO3)3 with excess chelating agents. After heat treatment above 800 °C, well-crystallized and highly (001)-oriented Y bFe2O4 started to epitaxially form on the substrate under controlled oxygen partial pressure with H2/CO2 gas mixtures. X-ray pole figure analysis confirmed the following epitaxial relationship: Y bFe2O4[100](001)//α-Al2O3[100](001). Moreover formation of an Fe3O4 interracial layer between Y bFe2O4 and α-Al2O3 was detected by high-resolution transmission electron microscopy. Presence of the Fe3O4 interracial layer seemed to release the lattice misfit with the substrate. The Fe2+/Fe3+ ratio in the obtained Y bFe2O4 films was nearly stoichiometric and the indirect bandgap assigned to Fe2+ → Fe3+ charge transfer excitation was found to be ∼0.4 eV by optical spectroscopy. A clear magnetic transition from the paramagnetic state to the ferrimagnetic state occurred at ∼230 K.

Single domain growth and charge ordering of epitaxial YbFe2O4 films

“…It must be mentioned that the remanent magnetization values at lower temperatures were comparable to those of bulk single crystals, 7,32 and were more than one order of magnitude larger than those of thin film samples in earlier studies. 19,20,22,23,25,26 The large deviation between the field-cooled (FC) and zero-field-cooled (ZFC) curves in Figure S2 indicates that the obtained films possessed large uniaxial magnetic anisotropy along the c-axis. Thus the ZFC magnetization curves had a sharp cusp 33 near the TN even with a magnetic field of 5 kOe.…”

“…It is noteworthy that the YbFe2O4-δ films reported previously showed six-fold symmetric patterns owing to the formation of double-domain structure. 21,25 However, using the sputtering deposition technique, the epitaxial YbFe2O4-δ films exhibiting a nearly single-domain structure were successfully formed on the YSZ (111) substrates. This may be the reason the resulting films had a large magnetization comparable to that of bulk single crystal.…”

“…[15][16][17][18] Later, with the successful fabrication of well-crystallized Fe3O4 films, many research groups have attempted to fabricate well-defined RFe2O4 films intended for device applications. Epitaxial c-axis oriented RFe2O4 films were grown on various substrates such as yttria-stabilized zirconia (YSZ) (111), [19][20][21] MgO (111), 22,23 α-Al2O3(0001), 11,[24][25][26] ZnO (001), 27 MgAl2O4 (111), 22 and 6H-SiC (001). 22 However, to the best of our knowledge, no study presenting the charge-ordered superstructure of prepared films exists, except those on the epitaxial YbFe2O4 films on α-Al2O3(0001) with Fe3O4 Please do not adjust margins Please do not adjust margins buffer layers.…”

“…In the present study, we attempted to prepare stoichiometric and epitaxial YbFe2O4 films with a single-domain structure using an RF magnetron sputtering method. In our previous study, 25,26 α-Al2O3(0001) substrates were used instead of YSZ (111) singlecrystalline substrates. α-Al2O3 has a corundum structure, while YSZ has a fluorite structure.…”

Optical and Electro-Optical Properties of YbFe2O4 Thin Films

“…Although there has been a decent amount of work on YbFe 2 O 4 , most of the published articles have been on the bulk samples and there is only a small number of studies on YbFe 2 O 4 thin films. [34,35,36,37] Additionally, the systematic studies on the optical properties and electronic excitations of YbFe 2 O 4 are very limited. Since both ferroelectric and magnetic properties of YbFe 2 O 4 come from the Fe d electrons, understanding of the electronic transitions and their temperature dependence is very important.…”