Abstract Stoichiometric gallium ferrite (GFO) is a promising single-phase multiferroic material at room temperature. Nevertheless, simultaneous magnetism and ferroelectricity in a single GFO at room temperature has not been demonstrated yet. In this work, single-phase GFO thin films with different amount of excessive Fe have been successfully grown using a dual target pulsed laser deposition (PLD) process, and the magnetic transition temperature is found to be above room temperature with excessive Fe distributed among the available cation sites of GFO unit cell. Ferroelectricity of GFO films have been confirmed by second harmonic generation (SHG), polarization hysteresis, pyroelectric reversal, and piezoresponse force microscopy (PFM), and magnetoelectric (ME) coupling has been demonstrated by increase in piezoresponse induced via external magnetic field applied in-plane, all measured at room temperature. From the data, it is theorized that the magnetic properties of GFO originate from the superexchange interaction mediated via the Fe1-O-Fe2 bond, and an additional Fe1-O-Fe* bond can form from excess Fe atoms. Under a magnetic field applied along c axis, the magnetic moment of Fe2 and Fe* increase while that of Fe1 decreases, and these changes in magnetic moment result in larger distortion of Fe2 and Fe* octahedrons along the b-axis, and thus enhanced polarization and piezoresponse. This series of studies thus confirm single-phase GFO with excessive Fe as a multiferroic material at room temperature with ME coupling, paving way for its potential functional applications in microelectronic and spintronic devices.

中文翻译：

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调节外延镓铁氧体薄膜中的 Fe 浓度以获得室温多铁性

摘要 化学计量镓铁氧体（GFO）是一种很有前途的室温单相多铁性材料。然而，在室温下单个 GFO 中同时具有磁性和铁电性尚未得到证实。在这项工作中，使用双靶脉冲激光沉积（PLD）工艺成功地生长了具有不同过量 Fe 的单相 GFO 薄膜，并且发现磁转变温度高于室温，过量的 Fe 分布在GFO 晶胞的可用阳离子位点。GFO 薄膜的铁电性已通过二次谐波产生 (SHG)、极化滞后、热电反转和压电响应力显微镜 (PFM) 得到证实，和磁电 (ME) 耦合已经通过面内施加的外部磁场引起的压电响应的增加得到证明，所有这些都是在室温下测量的。根据数据，理论上 GFO 的磁性源于通过 Fe1-O-Fe2 键介导的超交换相互作用，额外的 Fe1-O-Fe* 键可以由过量的 Fe 原子形成。在沿 c 轴施加磁场的情况下，Fe2 和 Fe* 的磁矩增大，Fe1 的磁矩减小，这些磁矩的变化导致 Fe2 和 Fe* 八面体沿 b 轴的畸变较大，从而增强极化和压电响应。因此，这一系列研究证实了在室温下具有过量 Fe 的单相 GFO 作为多铁性材料与 ME 耦合，