Multiferroic Properties of Nano-Structured Pb(Zr,Ti)Ox-CoFe2O4 Hybrid Material

Multiferroic materials have attracted much attention due to their interesting multifunctional properties and potential applications in future generations of memory devices. Pb(Zr,Ti)O3/CoFe2O4 (PZT/CFO) double-layer thin films were proved to have good magnetoelectric (ME) effect, thus motivating the investigation of three-dimensional and nano-scaled PZT/CFO architecture to increase memory density and optimize multiferroic properties. In this work, mesoporous CFO thin film were formed by evaporation-induced self-assembly with pores of 14 nm in diameter and exhibited ferromagnetism with saturation magnetization of 9x10-4 emu and coercivity of 1200 Oe at room temperature. Ultra-thin PZT films were synthesized by atomic layer deposition at a deposition rate of 0.7 nm/cycle and a 14-nm thick film presented remanent and saturation polarization of 4.3 and 7.9 µC/cm2, and a coercive electrical field (Ec) of 1.26 MV/cm. Combining the porous CFO with a uniform and conformal coating of 5-7 nm PZT films, a nano-structured PZT-CFO hybrid material was formed and confirmed by scanning electron microscope (SEM), transmission electron microscope (TEM) and ultraviolet photoelectron spectroscopy (UPS) measurements. To assess multiferroic properties of the PZT/CFO composite, superconducting quantum interference device (SQUID) magnetometry was used. When the samples were measured in-plane, the saturation magnetization was relatively constant at 7.8x10-4 emu after electrical poling at 1kV/cm. While the samples were measured out-of-plane, the saturation magnetization decreased from 9.0x10-4 to 8.5x10-4 emu after electrical poling at 1kV/cm. Polarization voltage (P-V) measurement is underway and so far the promising results indicate ALD enables the synthesis of a PZT-CFO composite with magnetoelectric coupling effect and potential in memory applications.