Magnetic and structural characteristics of multiferroic Fe₃O₄/(Bi_3.25Nd_0.65Eu_0.10)Ti₃O₁₂ composite thin films deposited by metalorganic chemical vapor deposition

Abstract

Ferromagnetic magnetite (Fe3O4) thin films for magnetoelectric multiferroic applications were deposited on (200) (Bi3.25Nd0.65Eu0.10)Ti3O12 (BNEuT)/(101) Nb:TiO2 substrates by metalorganic chemical vapor deposition (MOCVD) using an iron(III) tris(2,2,6,6-tetramethyl-3,5-heptanedionato) precursor as the iron source. The BNEuT film utilized as a ferroelectric template material was in the form of freestanding nanoplates with narrow spaces between them. The effects of deposition conditions such as the deposition time and substrate temperature on the magnetic and structural characteristics of the Fe3O4/BNEuT composite films were investigated. All the films consisted of mostly single-phase Fe3O4 with a cubic inverse-spinel structure. When deposition was carried out at temperatures of 400–420 °C, the filling rates of particles introduced into the narrow spaces between the BNEuT nanoplates exhibited high values of 76–89% including the amorphous phase. This suggested that the deposition in this temperature range made progress according to the growth mechanism of MOCVD in the surface reaction rate determining state. Room-temperature magnetic moment–magnetic field curves for Fe3O4 thin films deposited at 400–500 °C for 60 min exhibited narrow rectangular hysteresis loops, indicating typical soft magnetic characteristics.

Fabrication and leakage current and ferroelectric characteristics of multiferroic Fe3O4/(Bi3.25Nd0.65Eu0.10)Ti3O12composite thin films with Fe3O4magnetic electrodes micropatterned by reactive ion etching

“…The existence of 220, 311, 511, and 440 diffraction peaks suggests that the Fe 3 O 4 is polycrystalline, which is consistent with the ring-like selected area electron diffraction patterns observed in our previous study. 20) Figure 4 shows the surface FE-SEM images of (a) a BNEuT ferroelectric template film and Fe 3 O 4 =BNEuT composite films deposited for (b) 30, (c) 60, and (d) 90 min by MOCVD. Figure 4(a) shows characteristic BNEuT nanoplates with a height of 1.9 µm and a width of 50-100 nm stacked along the [001] direction.…”

“…The MOCVD system had a single metalorganic precursor delivery system, and has been described in detail elsewhere. 20) Each film was deposited on a 1.9-µm-thick (200) BNEuT=(101) Nb:TiO 2 substrate at a substrate temperature of 500 °C under a carrier gas flow rate of 100 sccm and an oxidizing gas flow rate of 300 sccm. To investigate the effects of the Fe 3 O 4 electrode thickness on the electrical properties of the composite films, deposition times of 30, 60, and 90 min were used.…”

“…To minimize clamping effects [1][2][3] due to the presence of a substrate, and achieve enhanced multiferroic (MF) properties (ferroelectricity and ferromagnetism) and a large magnetoelectric (ME) effect, [4][5][6][7][8] we fabricated nanopillar-type MF composite devices by depositing the ferromagnetic material magnetite (Fe 3 O 4 ) [9][10][11][12][13][14] on (200) (Bi 3.25 Nd 0.65 Eu 0.10 )Ti 3 O 12 (BNEuT)=(101) Nb:TiO 2 substrates [15][16][17] by metalorganic chemical vapor deposition (MOCVD) 18,19) in our previous study. 20) We succeeded in achieving a high magnetite particle filling rate of approximately 90% in narrow spaces between BNEuT nanoplates. The substrate temperature during MOCVD was found to be the dominant factor influencing both the filling rate and the crystallinity of the magnetite particles.…”

Effects of post-annealing temperature and micropillar shape on physical properties of micropillar-type multiferroic composite thin films

“…15) In our previous study, we have successfully fabricated a-axis oriented (Bi 3.25 Nd 0.65 Eu 0.10 )Ti 3 O 12 (BNEuT) nanoplates with a unique nanoplate structure and large remanent polarization (2P r = 66 μC cm −2 ) at room temperature. [16][17][18] The MF composite films were fabricated by utilizing the gaps in the nanoplate structure, 19,20) but the ME effect could not be clearly observed due to the small amount of ferromagnetic material introduced in the small gaps. Therefore, ferroelectric micropillar structure controlled sizes of gaps were fabricated by reactive ion etching (RIE).…”

Crystal structure and ferroelectric polarization of tetragonal (Bi1/2Na1/2)TiO3–12BaTiO3

“…The polarization twist is considered as the possible origin of the superior piezoresponse of BNT-BT at the MPB compositions. We expect that controlling the structural coupling between polarization and rotation distortion can provide a framework for designing polar perovskites exhibiting a wide variety of functionalities such as dielectric, 42) piezoelectric, 33,43,44) multiferroic, 42,[45][46][47] and photovoltaic [48][49][50][51][52] properties. Understanding the crystal structure variations at MPB compositions, such as the P4bm-P4mm phase transition, is essential for elucidating the mechanism in the enhanced piezoelectric properties.…”