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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.37

Magnetic properties of Single Crystal GaFeO3 Koki Tachiyama1, Shintaro Yasui1, Badari Narayana Aroor Rao1, Takuro Dazai1, Takamasa Usami1, Tomoyasu Taniyama1, Tsukasa Katayama2, Yosuke Hamasaki3, Jianding Yu4, Huan He4, Hui Wang4, and Mitsuru Itoh1 1 Laboratory for Materials and Structures, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8503, Japan

2

Department of Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan

3

Department of Applied Physics, National Defence of Academy, Yokosuka 239-8686, JAPAN

4

Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, P.R. China 200050

Abstract

-Al2O3-type GaFeO3 is a promising multiferroic material due to the coexistence of a large spontaneous magnetization and polarization near room temperature. In the current study, we present the magnetic properties of single crystalline GaFeO3 and compare it with that of Fe2O3. Magnetic measurements revealed that spontaneous magnetization appears below 540 K in two steps, similar to that reported for Fe2O3. Partial magnetic ordering takes place at 540 K (TN1), with Fe3+ ions in two distorted octahedral sites ordering antiparallel to one another. Upon further cooling at 200 K (TN2), the remaining Fe3+ ions in regular octahedra and tetrahedra order antiparallel to one another. Substitution of Ga for Fe in -Fe2O3 leads to a decrease in TN1 and TN2 from 850 to 540 K and from 480 to 200 K, respectively, caused by a dilution of magnetic Fe by nonmagnetic Ga and preferential site occupation of Ga. [email protected]

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INTRODUCTION Among multiferroic materials, -Al2O3-type oxides—isostructural with -Fe2O3 and GaFeO3—are promising due to the coexistence of a large spontaneous magnetization and polarization near and above room temperature as well as their multiferroic properties such as magnetic-field-induced modulation of polarization [1-11]. GaFeO3, a multiferroic material of longstanding history, is the sole known thermodynamically stable phase among -Al2O3-type oxides, AxFe2-xO3 (A=Al [12,13], (Ga,Cr) [14,15], (Ga,Mn) [14], Ga [1,3,16], Fe [2,6,17], Rh [18,19], and In [20]). GaFeO3 has an orthorhombic structure with a space group of Pna21 (No.33) and consists of two distorted octahedral Fe1d and Fe2d sites, one regular octahedral Fe3r site and one tetrahedral Fe4t site (Figure 1). It exhibits ferrimagnetism with a high magnetic transition temperature due to the superexchange interaction between the Fe ions at the Fe1d and Fe2d sites and those at the Fe1d and Fe3r sites [1]. The ferrimagnetism can also be adjusted to be above room temperature by changing the Ga/Fe ratio [1-4]. Furthermore, spin-orbit coupling due to the strong hybridization between the orbitals of Fe 3d5 at the