Magnetoelectric and multiferroic properties of variously oriented epitaxial BiFeO3–CoFe2O4 nanostructured thin films

Abstract

We report the ferroelectric, ferromagnetic, and magnetoelectric ͑ME͒ properties of self-assembled epitaxial BiFeO 3 -CoFe 2 O 4 ͑BFO-CFO͒ nanostructure composite thin films deposited on ͑001͒, ͑110͒, and ͑111͒ SrTiO 3 ͑STO͒ single crystal substrates. These various properties are shown to depend on orientation. The maximum values of the relative dielectric constant, saturation polarization, longitudinal piezoelectric coefficient, saturation magnetization, and ME coefficient at room temperature were 143, 86 m / cm 2 , 50 pm/V, 400 emu/cc, and 20 mV/ cm Oe, respectively.

Giant magnetoelectric torque effect and multicoupling in two phases ferromagnetic/piezoelectric system

“…As the multi-coupling ME effect is considered, the anomaly that the ME coefficient of T-L mode were slightly higher than that for L-L mode in (001) BF-CF/STO self-assemble (1-3) structure nano composite could be easily explained. 31 Although the ME contribution from the magnetostriction for T-L mode (d 31 prefer) is much smaller than that for the L-L mode (d 33 prefer), the ME contribution from magnetic torque for the T-L mode (bending prefer) is much larger than that for the L-L (expanding prefer) mode, which in multi-coupling combination leads to a higher ME effect in the T-L mode than that in the L-L mode.…”

Quantitative determination of anisotropic magnetoelectric coupling in BiFeO3–CoFe2O4 nanostructures

“…6 One dominant reason for this difficulty is that the ME voltage signal is proportional to the film thickness; it typically becomes smaller than 1 V for film thicknesses less than 1 m. To overcome this difficulty, a large ac magnetic field ͑H ac ͒ of up to ϳ1 kOe was recently used to obtain the effective MES as a function of H ac . 7,8 However, direct measurements of the MES based on a conventional scheme that employs small H ac values with variations in the dc magnetic field ͑H dc ͒ would be useful for understanding the ME coupling of numerous multiferroic films or nanostructures at the quantitative level. In this work, by use of the conventional scheme, we provide experimental evidences that a 300 nm thick BiFeO 3 -CoFe 2 O 4 ͑BFO-CFO͒ nanostructure has a peculiar MES anisotropy that is not expected in bulk forms of those materials.…”

“…Although there might exist several mechanisms to induce enhanced ␣ 31 as discussed in a recent anisotropic MES study using large H ac , 8 one most decisive factor could be the preferred magnetic domains existing in the CFO nanopillars. The solid lines in Fig.…”

Measuring the magnetoelectric effect across scales

“…Thus, typically the internal structure of thin films and epitaxial layers are determined by the quality of the initial wafer surface and the subsequent film deposition steps and techniques. An example of magnetoelectric composite films is given in [75] investigating the influence of substrate orientation on film growth. Columnar films were grown on different crystal orientations of SrTiO 3 .…”