Ferrimagnetism and Ferroelectricity in Cr-Substituted GaFeO₃ Epitaxial Films

Abstract

GaFeO3-type iron oxides are promising multiferroic materials due to the coexistence of a large spontaneous magnetization and polarization near room temperature. However, magnetic substitution, which is a general method to control multiferroic properties, is difficult due to instability of the substituted GaFeO3. In this study, Ga0.5Cr0.5FeO3 epitaxial thin films are successfully fabricated through epitaxial stabilization. These films exhibit in-plane ferrimagnetism and out-of-plane ferroelectricity simultaneously. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements of the Ga0.5Cr0.5FeO3 film reveal that the oxidation states of the Fe and Cr ions are trivalent. In addition, some Fe ions are located at tetrahedral Ga1 sites. Compared to the GaFeO3 film, the Ga0.5Cr0.5FeO3 film shows a higher magnetic phase transition temperature (240 K), weaker saturation magnetization at 5 K, and a unique temperature dependence of the magnetization behavior. The effects of Cr substitution on the magnetic properties are strongly affected by the sites of the Fe3+ (3d5) and Cr3+ (3d3) ions. Furthermore, room-temperature ferroelectricity in the GaFeO3 and Ga0.5Cr0.5FeO3 films was demonstrated. Interestingly, the change in the ferroelectric parameters via Cr substitution is very small, which disagrees with the previously proposed polarization switching mechanism. Our findings are key to understanding the genuine polarization switching mechanism of the multiferroic GaFeO3 system.

High Interfacial Hole‐Transfer Efficiency at GaFeO3 Thin Film Photoanodes

“…This article describes, for the first time, the unique PEC properties of GaFeO 3 (GFO), a ferrite widely investigated in the context of ferroelectric systems. [ 23–26 ] One of the unique aspects of this material is the high density of cation disorder due to the similar ionic radii of Ga 3+ and Fe 3+ . Polycrystalline GFO thin films are prepared by sol–gel methods exhibiting a high degree of phase purity (orthorhombic with the Pc 21 n space group) featuring over 150 X‐ray diffraction (XRD) peaks, as well as 25 different Raman modes that are assigned to Ga and Fe sites in octahedral and tetrahedral coordination.…”

Chemical design of a new displacive-type ferroelectric

“…The ionic radii for Ba(XII), Sr(XII), and Ca(XII) are 1.61, 1.44, and 1.34 Å, respectively. In the case of (Ba,Ca)TiO 3 , off-centering of Ca 2+ from the central position was confirmed by theoretical calculation to result from the cooperative shift of Ca 2+ by 0.12 Å along the [113] direction (Fig. 7d).…”

“…In the case of Bi 2 SiO 5 87 and BeO, 93 an elevated temperature was required to obtain an opened D-E loop. The well-controlled stoichiometry in epitaxially grown thin films of AFeO 3 (A = (Al,Fe), 111 Ga, 112 (Cr,Ga), 113 Fe, 114 (Rh,Fe), 115 (Al,Ga), 116 (Sc,Ga), 116 and (In,Ga) 116 ) enabled D-E loop measurements; however, the observed polarization was 1-5 μC cm −2 , which is an order of magnitude smaller than the calculated value of 21-26 μC cm −2 (Table 2). This mismatch originates from the collision of the displacive motions along the ±a directions among adjacent nanodomains typically 10-20 nm wide and oriented in three different directions inside the c-plane (see Fig.…”

Mössbauer measurements of GaFeO3 single crystal multiferroic

“…However, the mechanism of polarization switching is still under debate. Also, the observed electrical polarization switching in Cr doped GaFeO 3 films [22] seems to be inconsistent with the switching mechanism proposed in [23,21]. Magnetoelectric effect, resulting in coupling of magnetization and electrical polarization is studied intensively.…”