Self‐Assembled Growth of BiFeO₃–CoFe₂O₄ Nanostructures

Abstract

Multifunctional materials have attracted increasing interest in recent years because of their potential applications in novel technological devices. [1][2][3][4][5][6][7][8][9][10][11] [12] The ferroelectric and magnetic properties as well as the degree of the coupling are critically dependent on the morphology of the nanostructures, including domain patterns and shapes as well as the interfaces. In order to pursue the enhanced multifunctionality, significant effort has been made on understanding the growth mechanism and controlling the morphology of the nanostructures. The morphology adopted by a crystalline material when it nucleates on a substrate surface is one of the fundamental issues of heteroepitaxy. Depending on the surface energy terms, i.e., substrate surface energy c 1 , interface energy c 12 , and surface energy of the crystalline phase c 2 , the equilibrium shape of a crystalline nucleus on a substrate can be determined using the Winterbottom construction.[13] The possible configuration of the crystalline nucleus on the substrate is a Wulff shape that has been cut off by the substrate, translated by the signed distance Dc from the origin. Dc is the wetting strength, which is the energy difference obtained by replacing the substrate surface with an interface, Dc = c 12 -c 1 . In the BiFeO 3 -CoFe 2 O 4 system, BiFeO 3 has a distorted perovskite structure (R3c) [14] and CoFe 2 O 4 has a cubic spinel structure (Fd3m). CoFe 2 O 4 is characterized by the lowest surface energy of {111} surfaces, which is reflected in an equilibrium shape of an octahedron bounded by eight {111} facets. [15,16] In contrast, most perovskite phases have the lowest energy surfaces of {001} surfaces and a corresponding equilibrium shape of a cube dominated by six {100} facets. [17][18][19][20]

Probing electric field control of magnetism using ferromagnetic resonance

“…The room temperature single-phase multiferroic, BiFeO 3 (BFO), has attracted a lot of recent research interest due to the coexistence of robust ferroelectricity (P) and antiferromagnetism (L) [13][14][15][16][17][29][30][31][32][33][34][35][36] and a weak canted magnetic moment (M C ). In bulk BFO, the weak moment results from the canting of the magnetic sublattices due to the Dzyaloshinskii-Moriya interaction 14 as predicted by the density functional theory 14 and confirmed experimentally 30,36 .…”

Magnetic-field-induced phase separation via spinodal decomposition in epitaxial manganese ferrite thin films

“…The 0 G Mn ferrite film has a pyramid-like domain structure which seems to be faceted along (111) planes. Previously, it was reported that spinel oxide nanostructures of CoCr 2 O 4 on MgO (001) [26] or CoFe 2 O 4 on SrTiO 3 (001) [27] substrates tend to grow into pyramid-like grains along {111} planes to minimize the surface energy. It has to be noted that the surface energy in spinels is strongly anisotropic, with the {111} planes having the minimal surface energy [27].…”

Magnetic-field-induced spontaneous superlattice formation via spinodal decomposition in epitaxial strontium titanate thin films

“…If the period is determined by thermal diffusion, then it should be inversely proportional to the growth rate. 28,29 Figure 4b shows the change of the in-plane and out-of-plane lattice parameters with the deposition rate. This figure shows the in-plane lattice parameter as constant within error, irrespective of the deposition rate.…”