Abstract
A La0.67Sr0.33MnO3 (LSMO) ferromagnetic layer and a Nd3+/Hf4+ co-substituted Bi4Ti3O12 (Bi3.15Nd0.85Ti3-xHfxO12 (BNTHx, x = 0, 0.025, 0.05, 0.1 and 0.15)) ferroelectric layer were successively deposited onto the (00 l)-oriented LaNiO3 (LNO) layer buffered (001) Si substrate via all chemical solution deposition (CSD) method. As a result, the BNTHx/LSMO ferromagnetic-ferroelectric composite films integrated on Si substrate exhibit high c-axis orientation. The Nd3+/Hf4+ co-substituted BNTHx films have the lower leakage current and the better ferroelectric properties than the mono-substituted Bi4Ti3O12 (Bi3.15Nd0.85Ti3O12 and Bi4Ti2.95Hf0.05O12) films. In particular, the BNTH0.05/LSMO/LNO film has the lowest leakage current density of 2.5 × 10−7 A/cm2 at 200 kV/cm, and the highest remnant polarization (Pr) of 27.3 μC/cm2. The BNTH0.05/LSMO/LNO composite film also exhibits the soft ferromagnetism characteristics with a high saturated magnetization of 258 emu/cm3 at 300 K, and the excellent magnetoelectric (ME) effect. The variations of ME voltage coefficient αE values with DC bias magnetic field Hbias shows that the BNTH0.05/LSMO/LNO film has the high αE value at near zero Hbias. Moreover, at Hbias = 0 Oe, the αE value gradually increases from zero with the increasing of the AC magnetic field frequency, and eventually reaches about 18.9 V/cm·Oe at 100 kHz, suggesting the existence of self-biased ME effect.
Highlights
In multiferroic magnetoelectric (ME) materials, the coexistence of ferromagnetic and ferroelectric properties provides a possibility to obtain “magnetoelectric (ME) effect”, by which an induced electrical polarization and magnetization can be controlled by applying a magnetic and electric field, respectively
The crystal structure and crystalline orientation of all films were characterized by low-angle and theta-2theta X-ray diffraction
The diffraction peaks from the LNO and LSMO layers were satisfactorily indexed on the base of a cubic cell for LNO, and a rhombohedral cell for LSMO (JCPDS 50-0308), respectively
Summary
In multiferroic magnetoelectric (ME) materials, the coexistence of ferromagnetic and ferroelectric properties provides a possibility to obtain “magnetoelectric (ME) effect”, by which an induced electrical polarization and magnetization can be controlled by applying a magnetic and electric field, respectively. The ME effect of the available single-phase magnetoelectric materials is usually weak at low temperature It has attracted many researchers from the multiferroic ME field to develop new ferromagnetic-ferroelectric composite materials. To combine the ferromagnetic-ferroelectric composite film with other functional materials and develop new multi-functional devices, it would be very necessary for the ferromagnetic-ferroelectric layered film to orientedly grow onto the Si substrate[30]. For this strategy, some buffer layers must be used. To our knowledge, any work on the deposition of oriented lead-free ferromagnetic-ferroelectric composite films including the bismuth-layered perovskite phase on LNO buffered Si substrates are barely reported. The crystalline, microstructure, ferroelectric and ferromagnetic properties, and ME coupling effect of the as-prepared ferromagnetic-ferroelectric composite films were discussed in detail
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