Room Temperature Magnetically Ordered Polar Corundum GaFeO₃ Displaying Magnetoelectric Coupling

Abstract

The polar corundum structure type offers a route to new room temperature multiferroic materials, as the partial LiNbO-type cation ordering that breaks inversion symmetry may be combined with long-range magnetic ordering of high spin d cations above room temperature in the AFeO system. We report the synthesis of a polar corundum GaFeO by a high-pressure, high-temperature route and demonstrate that its polarity arises from partial LiNbO-type cation ordering by complementary use of neutron, X-ray, and electron diffraction methods. In situ neutron diffraction shows that the polar corundum forms directly from AlFeO-type GaFeO under the synthesis conditions. The A/Fe cations are shown to be more ordered in polar corundum GaFeO than in isostructural ScFeO. This is explained by DFT calculations which indicate that the extent of ordering is dependent on the configurational entropy available to each system at the very different synthesis temperatures required to form their corundum structures. Polar corundum GaFeO exhibits weak ferromagnetism at room temperature that arises from its FeO-like magnetic ordering, which persists to a temperature of 408 K. We demonstrate that the polarity and magnetization are coupled in this system with a measured linear magnetoelectric coupling coefficient of 0.057 ps/m. Such coupling is a prerequisite for potential applications of polar corundum materials in multiferroic/magnetoelectric devices.

Magnetostriction-polarization coupling in multiferroic Mn2MnWO6

“…Remarkable physical properties, such as multiferroic, piezoelectric, pyroelectric and second harmonic generation (SHG) effect, have been demonstrated in these materials. For example, the coexistence of weak ferromagnetism and ferroelectricity has been observed in the high-pressure LN-type FeTiO 3 and in recently-reported GaFeO 3 2, 14 , and non-hysteretic colossal magnetoelectricity was found in collinear antiferromagnetic (AFM) NTO, which is, to the best of our knowledge, the only experimentally observed magnetoelectric coupling in the double corundum family 5 . In contrast to the off-centering displacement of d 0 B cations in the octahedra occurring in many ferroelectric perovskites 15–17 , in corundum-type AB O 3 or A 2 BB ’O 6 materials, the polarization reversal is driven by the small A or B cations moving between oxygen octahedra 18, 19 , hence the d 0 configuration is not required.…”

“…The structural features of corundum derivatives provide an ideal platform for designing polar and magnetic compounds, since magnetic ions can be incorporated into both the octahedral A - and B -sites to lead to strong magnetic interactions, accompanied by large spontaneous polarization ( P S ) if the polar LiNbO 3 (LN, R 3 c ), ordered ilmenite (OIL, R 3), or Ni 3 TeO 6 (NTO, R 3) type structure is adopted 1–14 . Remarkable physical properties, such as multiferroic, piezoelectric, pyroelectric and second harmonic generation (SHG) effect, have been demonstrated in these materials.…”

Use of Ga2O3[1 0 0] monocrystals as substrates for the synthesis of GaFeO3 thin films

“…This is important since electric-field control of magnetism requires less energy than the use of magnetic fields [1]. GFO exhibit magnetoelectric properties [2][3][4][5][6][7] and high quality films can be deposited by pulsed laser deposition [8][9][10][11][12][13]. In a recent work, laser molecular beam epitaxy growth protocol was reported and based on the sequential deposition of Ga 2 O 3 and Fe layers followed by a thermal treatment [14].…”

Electric field controlled magnetic exchange bias and magnetic state switching at room temperature in Ga-doped α-Fe2O3 oxide

“…Some of the hematite derived systems (GaFeO3, FeTiO3) in orthorhombic phase showed magnetoelectric properties at lower temperatures [22][23][24] and some compositions in thin film form (e.g., Mn doped Ga0.6Fe1.4O3:Mg [25] and GaFeO3 [26]) showed magnetoelectric properties at room temperature. Further, hematite (α-Fe2O3) derivatives in corundum (rhombohedral) structure offers electrically polar and room temperature multiferroic materials [27][28].…”