Fabrication and Characterization of Multiferroic Al 0.5 Fe 1.5 O 3 Epitaxial Thin Films
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.121
Fabrication and Characterization of Multiferroic Al0.5Fe1.5O3 Epitaxial Thin Films Badari Narayana Aroor Rao1, Shintaro Yasui1, Tsukasa Katayama2, Mitsuru Itoh1 1
Laboratory for Materials and Structures, Tokyo Institute of Technology, Japan
2
Department of Chemistry, The University of Tokyo, Japan
ABSTRACT
Single-phase multiferroic materials have attracted considerable attention among scientists, due to the strong drive in industry towards device miniaturization, addition of new functionalities, etc. Currently, most of the discovered materials have at-least one ferroic order active only at low temperatures, thereby hindering their induction into practical devices. κAl2O3-type AlxFe2-xO3 (x-AFO) oxides belong to a new class of metastable multiferroic compounds (space group: Pna21), with relatively high Curie temperatures. The current work investigates the effect of thin film deposition conditions on the ferroelectric and ferrimagnetic properties of Al0.5Fe1.5O3 (0.5-AFO). Substrate temperature and oxygen partial pressure during deposition were found to be the critical parameters in obtaining high quality films. Optimizing the deposition conditions of 0.5-AFO enabled observation of both ferroelectricity and ferrimagnetism at room temperature.
INTRODUCTION Single-phase multiferroic materials are attractive, due to the various advantages like new functionalities, device miniaturization, low energy consumption, etc. [1–5]. However, most of the multiferroic materials currently known, function only at low temperatures, thereby limiting their use in practical applications [6,7]. Recently, a new class of materials with κ-Al2O3 structure have been discovered [e.g. GaxFe2-xO3 (x-GFO), ε-Fe2O3, AlxFe2-xO3 (x-AFO)], which are promising as room temperature multiferroics [8–16]. Of these compounds, AlxFe2-xO3 (x-AFO) is interesting, since it uses cheap and environment friendly raw materials. It crystallizes in the κ-Al2O3 structure with the polar orthorhombic space group Pna21 [11,16,17]. The polar symmetry of the structure indicates its potential to exhibit ferroelectricity. The polarization mechanism in these class of materials is not entirely clear, and is understood to be a complex process
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[16,18,19]. On the other hand, ferrimagnetism originates in x-AFO due to disordered but unequal distribution of Fe and Al in each of the four cation sites [11,16]. Recently, Hamasaki et al. successfully synthesized epitaxial thin films of xAFO on (111)SrTiO3 substrates [11,17]. However, high leakage currents in the films, possibly due to presence of oxygen vacancies, made direct ferroelectric measurements at room temperature difficult, and only local information using piezoresponse force microscopy (PFM) could be obtained. T
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