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Electric Transport Characteristics of Gallium Iron Oxide Epitaxial Thin Film Tsukasa Katayama, Shintaro Yasui, Yosuke Hamasaki, and Mitsuru Itoh Laboratory for Materials and Structures, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8503, Japan

ABSTRACT A Ga0.8Fe1.2O3 epitaxial thin film was fabricated on a SrTiO3(111) substrate using pulsed laser deposition. The film is c-axis-oriented and has multiple in-plane domains. In-plane magnetization measurements show that it exhibits ferrimagnetic behavior with a Curie temperature (TC) of 290 K. The insulating film exhibits hopping conduction with a resistivity (ρ) of 4 × 105 Ωcm at 300 K. The ρ value is four orders lower than that of a BiFeO3 film, probably owing to the formation of multiple in-plane domains in the Ga0.8Fe1.2O3 film. Positive magnetoresistance with a maximum value of 3.5% near TC was observed, suggesting that antiferromagnetic interaction between Fe3+ ions decreases carrier transfer between the ions.

INTRODUCTION Multiferroics are interesting materials that display simultaneous electric and magnetic orders. They were recently reported to be useful for future applications such as spin-filter-type tunnel junctions [1] and resistive switching memory elements [2,3]. In these devices, multiferroic materials are employed as a carrier transfer layer, so it is necessary to investigate the transport properties of these materials. GaFeO3 (GFO)-type iron oxides are promising multiferroic materials owing to the coexistence of spontaneous polarization and magnetization near and above room temperature [4– 11]. They exhibit ferrimagnetic properties with a controllable Curie temperature (TC) [4,5]. Ferroelectric features are also observed at room temperature in GaxFe2-xO3 (x = 0–1) epitaxial thin films [6–9]. However, although their magnetic and dielectric properties have been investigated, reports on their transport properties are very few [10,11]. Therefore, in this study, we fabricated a Ga0.8Fe1.2O3 epitaxial thin film and investigated its magnetic and transport properties. The film undergoes a ferrimagnetic to paramagnetic transition near room temperature,

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at 290 K. Its in-plane resistivity behavior is insulating and exhibits positive magnetoresistance (MR). The MR increases as the temperature approaches 300 K (near TC), suggesting that antiferromagnetic interaction between Fe3+ ions decreases electron transfer between the ions.

EXPERIMENT GFO-type Ga0.8Fe1.2O3 thin films were grown on SrTiO3(111) (STO) substrates by pulsed laser deposition (PLD). The composition was chosen because its TC is near room temperature [4,5]. We used a Ga0.8Fe1.2O3 ceramic pellet prepared from mixed powders of α-Fe2O3 and Ga2O3 by a solid-state reaction (sintering at 1500°C) as the PLD target. The substrate temperature and oxygen partial pre