Recently, multiferroic materials have provoked a renaissance because of the prospect of controlling both the dielectric and magnetic properties of these materials using a magnetic or an electric field. [1][2][3][4][5][6] Yet there are few materials that are simultaneously ferroelectric and ferromagnetic in the same phase. [7,8] The orthorhombic TbMnO 3 phase has attracted much attention owing to its intriguing coupling between spin and charge degrees of freedom, but its ferroelectricity emerges at temperatures below 27 K.[1] Here, we report on the multiferroic properties of a hexagonal TbMnO 3 metastable phase that was epitaxially stabilized in thin-film form on substrates with hexagonal in-plane symmetry. In contrast to the bulk orthorhombic phase, [1] the hexagonal TbMnO 3 films display ca. 20 times larger remnant polarization with the ferroelectric ordering temperature shifted to ca. 60 K. In addition, a newly discovered antiferroelectric-like phase and a clear signature of magnetoelectric effects suggest its uniqueness in the class of hexagonal manganites. Here we demonstrate a promising way to synthesize new multiferroic materials that do not exist in bulk form.Among the known multiferroic materials, the rare-earth manganites RMnO 3 are very intriguing material systems that can have two kinds of crystal structure. Depending on the size of the R ion, [9] RMnO 3 forms either an orthorhombic (R = La-Dy) or a hexagonal (R = Ho-Lu) structure. All of the hexagonal rare-earth manganites show multiferroic behaviors with high ferroelectric ordering temperatures, T C , (typically, above 590 K) and magnetic ordering temperatures T N ∼ 70-120 K.[3] The origin of the ferroelectric (FE) ordering in hexagonal manganites is related to the tilting of the rigid MnO 5 trigonal bipyramid.[10] By contrast, among the orthorhombic RMnO 3 , only the three compounds containing rare-earth elements near Ho (i.e., R = Dy, Tb, and Gd) show multiferroic behavior with a relatively low ferroelectric ordering temperature (ca. 27 K). [1,11] In this case, the ferroelectricity originates from the magnetic-frustration-induced lattice modulation. These facts imply that there is a possibility of controlling the multiferroic properties by modifying the structural phase of the rare-earth manganites.Since the orthorhombic TbMnO 3 is near the hexagonal RMnO 3 series, the formation energy difference between the orthorhombic and hexagonal TbMnO 3 could be small. Therefore, it is a worthwhile attempt to stabilize it in a hexagonal phase and explore its multiferroic properties. We fabricated TbMnO 3 in a new hexagonal phase by laser ablating the bulk orthorhombic materials into thin films on either Pt(111)//Al 2 O 3 (0001) or YSZ(111) (YSZ: yttria-stabilized zirconia) substrates. Note that the atomic arrangement on the surfaces of both substrates has hexagonal in-plane symmetry. In bulk, the TbMnO 3 exists in the distorted orthorhombic (GdFeO 3 -type) structure, as shown schematically in Figure 1a. The hexagonal in-plane symmetry on the substrate surface...

The authors fabricated Pb(Zr0.52Ti0.48)O3–NiFe2O4 composite films consisting of randomly dispersed NiFe2O4 nanoparticles in the Pb(Zr0.52Ti0.48)O3 matrix. The structural analysis revealed that the crystal axes of the NiFe2O4 nanoparticles are aligned with those of the ferroelectric matrix. The composite has good ferroelectric and magnetic properties. The authors measured the transverse and longitudinal components of the magnetoelectric voltage coefficient, which supports the postulate that the magnetoelectric effect comes from direct stress coupling between magnetostrictive NiFe2O4 and piezoelectric Pb(Zr0.52Ti0.48)O3 grains.

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