Fabrication and characterization of micropillar-type multiferroic composite thin films by non-aqueous sol-gel method using ferroelectric pillars

Abstract

CoFe2O4 (CFO) thin films were deposited on (Bi3.25Nd0.65Eu0.10)Ti3O12 (BNEuT) micropillar films by a non-aqueous sol-gel method. The pitch size of 2–5 μm in the micropillar films used as ferroelectric pillars, and 5 and 15 CFO deposition cycles were examined for high density of CFO nanoparticles. All the CFO films formed by five deposition cycles on BNEuT micropillar films with a pitch size of 2–5 μm were composed of mostly single-phase CFO with a cubic inverse-spinel structure. All the CFO films deposited on the four BNEuT micropillar films were highly dense and had excellent surface flatness, based on surface field-emission scanning electron microscope observations. Based on the structural, magnetic and ferroelectric characteristics, the optimal pitch size for achieving a high density of CFO nanoparticles was 5 μm, and the optimal number of CFO deposition cycles was five.

Fabrication and physical properties of microrod-type multiferroic composite thin films by metal organic decomposition

“…On the other hand, the Fe/Co ratio for the annealed samples gradually increases with increasing soaking time from 3 to 10 h. This suggests that the Co atoms diffuse upward from the bottom layer during high-temperature aging, as reported in other papers on the MOD and sol-gel methods. 1,27) Based on the above results, grain growth in CFO is thought to be accompanied by a transfer of Co atoms. The average Fe/Co ratio in the eight CFO layers for all samples was in the range 2.01-2.04, indicating a slightly Fe-rich composition compared to stoichiometric CoFe 2 O 4 .…”

“…In recent years, we have carried out studies on the synthesis and characterization of micropillar-type multiferroic (MF) composite thin films such as CoFe 2 O 4 /(Bi 3.25 Nd 0.65 Eu 0.10 )Ti 3 O 12 (CFO/BNEuT). 1,2) Most MF composite films consist of laminated structures of ferroelectric layers such as Pb(Zr,Ti)O 3 (PZT), BaTiO 3 or bismuth-layered structure compounds (BLSFs) deposited on a ferromagnetic layer such as cobalt ferrite (CFO). [3][4][5][6][7][8][9][10][11] The goal is to obtain a large magnetoelectric (ME) effect 9,[11][12][13][14][15][16] and to develop electric-magnetic energy conversion devices by reducing the clamping effect of the substrate to the utmost limit.…”

“…To achieve this, it is necessary to produce a template with a high aspect ratio by microfabricating the underlying thin film using reactive ion etching (RIE). [17][18][19][20][21] Based on the results of our previous studies, 1,2,22) we processed ferroelectric BNEuT thin films into microplates (MPs) and microrods (MRs), since ferroelectric materials containing dielectric metal elements (Bi, Nd, Eu, and Ti) exhibit high reactivity with chlorine compared with ferromagnetic materials containing transition metal elements (Co and Fe) in the RIE process. Using these underlying layers (ferroelectric pillars), we fabricated several MF composite films and examined their structural, magnetic, and electrical properties.…”

“…In this case, it was found that the optimal pitch was 5 μm. 1) Although these composite films are promising MF materials because they exhibit both ferroelectric and ferromagnetic order, no cross-correlation between the two types of order has been identified yet. Fabrication of CFO thin films using MOCVD requires expensive equipment, and complex process parameters such as the gas flow rate, temperature, and pressure must be controlled.…”